Getting the most from ForeFlight radar layers

Now that ForeFlight Mobile 7.7 introduced a second radar layer to the app, what are the practical advantages of each? As I mentioned in my earlier blog post, the composite reflectivity and lowest tilt radar layers both provide a high glance value to the pilot to highlight the location and movement of the truly nasty adverse weather. But I think you’ll find that these two layers are more often similar than they are different.

Go to any pilot gathering discussing weather and you’ll likely discover a majority of pilots genuinely swear by the composite reflectivity mosaic. In fact, you may even hear a few so-called “experts” stand up in front of an audience and attempt to convince them that you should only ever use composite reflectivity. Depending on your particular flying habits and aircraft capabilities, you may find that the base reflectivity from the lowest tilt is actually more useful and accurate. However, before we get into the pertinent differences, let’s examine how each mosaic is built.

The nuts and bolts of NEXRAD

Every NEXRAD radar site throughout the U.S. scans the sky with multiple 360-degree sweeps at increasing elevation angles. It starts the process (called a volume coverage pattern) at 0.5 degrees and finishes at 19.5 degrees assuming the radar is in precipitation mode. The base reflectivity from the lowest elevation angle (called the lowest tilt) is most representative of precipitation, if any, that is falling out of the base of the cloud and reaching the surface. So the lowest tilt is what interests most of the general public so that’s what you are likely to see on various websites that depict weather radar.

The composite reflectivity, on the other hand, includes the base reflectivity from every elevation scan. Depending on the scanning strategy of the particular radar site, this could be up to 14 different elevations. The highest base reflectivity value from each of these elevations is what’s included in the composite reflectivity mosaic. Consequently, you don’t know if the reflectivity depicted is near the base of the cloud, somewhere in the middle or near the top simply by looking at the mosaic.

Cross-section

A cross section of this mesoscale convective system (MCS) provides a better indication of the altitude of the highest reflectivity in the storm. In this case the precipitation core is below 6 km or 20,000 feet.

More is not always better

One of the chief issues with the composite reflectivity mosaic is that it often has a very large footprint when compared to the lowest tilt. It tends to exaggerate the areal impact of the precipitation event making it challenging to determine where it’s safe to fly. Shown below is a two image animation over the southeastern Florida peninsula that toggles between the composite reflectivity and lowest tilt. Notice on the composite reflectivity mosaic at least one-half of the area depicts returns that are not likely to be actual precipitation falling from the sky. Most of the green contours to the northeast of Lake Okeechobee are low dBZ returns from ice crystals in the thunderstorm’s anvil and are not likely a threat to pilots flying at lower altitudes 10 or more miles from the storm, but below the anvil.

CompositevsBase-Animation

An animation comparing the composite reflectivity and base reflectivity from the lowest elevation angle (lowest tilt).

High ice water content

If you fly a turbojet aircraft in the upper flight levels, the composite reflectivity mosaic can be quite important to examine. The thunderstorm anvil like the one shown above can contain a high enough concentration of ice crystals (called high ice water content) to be a problem. These ice crystals can be ingested into jet engines causing power-loss or damage within the engine core. Engine instability such as surge, stall, flameout, rollback and damage of compressor blades due to ice shedding have been reported in these conditions. So if you are a pilot circumnavigating deep, moist convection in a turbojet aircraft, the composite reflectivity mosaic provides some indication of where the high ice water content may be located.

Down low and below

During the warm season when thunderstorms are the most common, the lowest tilt depiction is one that is useful to pilots that like to fly down in the bumpy air below the cloud deck. Typically the footprint of the areas of precipitation will be less giving pilots a cleaner image leaving behind just the cellular structure that’s most important when flying within a convective environment. Even so, it’s still important to keep your distance. Bear in mind that nasty convective wind shear often occurs below building convection or when flying near mature thunderstorms. Gust fronts from thunderstorm outflow as well as microbursts are the biggest threats especially with high-base convection.

What about the radar from my Stratus?

At the moment, the base reflectivity from the lowest elevation angle isn’t part of the ADS-B broadcast. So while en route you will only have the regional and national composite reflectivity mosaic available. The current provider of ADS-B radar does a good job removing most non-precipitation returns, however, they don’t broadcast any returns below 20 dBwhich is typically what you’d see in areas with a thunderstorm anvil.

dBZ

Here is the ForeFlight mapping of colors to dBZ levels found in the Pilot’s Guide. Notice that the first shade of green under ADS-B doesn’t start until 20 dBZ whereas the Internet scheme starts as low as 5 dBZ.

In the end, when both depictions are available as they are in ForeFlight Mobile, each radar should be given its due time during your preflight analysis.

Getting The Lowdown On ForeFlight Radar

In the pilot world there is a ubiquitous debate that continues to thrive over what ground-based radar product is better to use – NEXRAD composite reflectivity or NEXRAD base reflectivity from the lowest elevation angle. Without question, both of these radar mosaics provide a high glance value to the pilot to highlight the location and movement of the truly nasty adverse weather along your proposed route assuming you understand each of their inherent limitations. Now in ForeFlight Mobile 7.7, you’ll have the opportunity to wrangle over which is best since we’ve added a high resolution base reflectivity layer from the lowest elevation angle to complement the current composite reflectivity layer within the app.

But wait…there’s more! In addition to this new layer, we now offer two new low resolution NEXRAD mosaics, namely, a composite reflectivity and lowest elevation angle base reflectivity layer. These two four-color ground-based radar mosaics comply with the dBZ-to-color mapping standards defined by the Radio Technical Commission for Aeronautics (RTCA) documented in Table 3.2 of DO-267A. More on these later.

Radar-Selection

You can now select from one of two radar mosaic depictions in ForeFlight Mobile. The selections include Composite reflectivity and reflectivity from the lowest elevation angle or Lowest Tilt.

Base does NOT equal lowest

First, let’s squash a misnomer about base reflectivity. Many pilots (and even weather professionals) may use the term “base” in base reflectivity to imply lowest. That’s not what it means. In fact, every elevation angle generated by the WSR-88D NEXRAD Doppler radars has a base reflectivity product. The amount of energy directed back to the radar is measured and recorded in a logarithmic scale called decibels of Z (abbreviated dBZ), where Z is the reflectivity parameter. Next, these base data returns are processed by a radar product generator (RPG) to produce hundreds of meteorological and hydrological products including a few near and dear to pilots such as reflectivity.

A more accurate description would be to prefix the product with the elevation angle such as “0.5 degree base reflectivity.” Nevertheless, you may see labels like “Composite Reflectivity” and “Base Reflectivity” on various public and subscription-based websites including those from NOAA. It’s likely that the base reflectivity is from the lowest elevation angle (or lowest tilt) of NEXRAD radar. That’s because the lowest elevation sweep is most representative of precipitation that is reaching the surface which is helpful to the average person on the street including hikers, golfers, boaters and anyone else who wants to know if they need to take the umbrella to work. Unfortunately, the elevation angle is usually dropped (likely due to ignorance or brevity) from these labels.

CompositevsBase-Animation

This is an animated comparison of the composite reflectivity and lowest elevation angle for convection in Florida. Notice the composite reflectivity provides a larger footprint since it picks up on the ice crystals that make up the cirrus anvil.

You might be surprised to learn that in many locations across the U.S., the composite reflectivity image you study before or during a flight is largely made up of only three or four of the lowest 14 elevation scans of the radar.  So in these areas the composite reflectivity and base reflectivity from the lowest elevation angle are not all that different. These areas include regions where the NEXRAD coverage is sparse. Which surprisingly doesn’t only occur in the western U.S. Places such as my home town of Charlotte, North Carolina have distinct gaps in radar coverage.

Radar to the max

Each NEXRAD radar makes multiple 360° azimuthal sweeps at increasing elevation angles from 0.5° to 19.5° depending on the current mode of operation. The number of elevation angles (or tilts) depends on the scanning strategy or Volume Coverage Pattern (VCP) of the individual radar which is set by the radar operator that is located at the local weather forecast office that monitors and manages that particular radar site. A composite reflectivity image considers the base reflectivity from all of the most recent sweeps at each elevation angle and shows only the maximum reflected energy in the vertical column above each location within the radar’s effective coverage area.

It’s all about range

With respect to ground-based radar, range or distance is the key.  Even though the lowest elevation angle is only 0.5°, at 124 nautical miles away the center of the radar beam is already nearly 17,000 feet above the surface due to the curvature of the earth.  So it is easy to see how the higher elevation angles may easily overshoot precipitation that is not in the immediate vicinity of a radar site. Moreover, even if the beam is low enough to see the storm, it may still overshoot the precipitation core.  Let’s take a look at an example.

Below is a two-image animation from the NEXRAD located at the Greenville-Spartanburg Weather Forecast Office in Greer, South Carolina. This shows the returns received from the lowest elevation angle or lowest tilt of the radar which is 0.5° and the fourth elevation angle which is only 1.7° (remember that 19.5° is the maximum elevation). Notice the radar at the lowest elevation has identified an area of weather over Fayetteville, North Carolina (seen on the far right). This cell is approximately 150 miles away from the radar site in Greer (on the far left). However, given it’s distance from the radar, the 1.7° elevation scan completely overshoots this area of precipitation. That means the composite reflectivity image in the Fayetteville area is likely made up of only the lowest three elevation angles of the radar. The remaining higher 11 elevation angles overshoot the precipitation in this region.

Angles

This two-image animation from WDT’s RadarScope app shows the base reflectivity from the 0.5 degree and 1.7 degree elevations. The NEXRAD radar producing this image is located in Greer, SC on the far left. Notice that some returns farther from the radar completely disappear as the radar beam overshoots the weather entirely.

Now it’s true that other adjacent radars such as the one from Raleigh Durham, North Carolina might be able to see this area of weather at higher elevation angles. However, due to the curvature of the earth, the radar beam from the highest elevation angles often overshoots much of the precipitation out there unless it is close to the radar site. This means that locations where there is little overlap between adjacent radars, expect the composite reflectivity image to be very similar to the base reflectivity image for the lowest elevation angle in these gaps.

The four-color radar

If you are flying with airborne radar, you may want to look at the new low resolution four-color NEXRAD mosaic now available in ForeFlight Mobile. The colors depicted in this radar mosaic match the standard color-to-dBZ mapping defined by the RTCA as documented in Section 3.8.2 (Table 3-2) of RTCA DO-267A (shown below). This standard is also used for airborne radar displays.

RTCA radar

This is Table 3.2 of DO-267A that defines the color-to-dBZ mapping for airborne radar.

To see the four-color radar depiction, simply select one of the two radar layers on the Map view. Then tap the gear button next to the Map mode button and scroll down the Settings window until you see the setting switch labeled Four-color Radar just above the Radar Opacity slider. Tapping on the right side of this switch will change the radar depiction from the high resolution radar mosaic to the four-color mosaic. You can also find this four-color switch in the general Map View settings.

4-color setting

The four-color radar switch is located in the general Map View settings or can be found under the gear button at the top of the Map view.

If you use the Stratus (FIS-B) to receive weather while in flight, you won’t find the capability to select the lowest tilt, but you will find the four-color radar will also be available for the composite reflectivity mosaic. As you can see below, the four-color radar mosaic (second image) provides a much more ominous depiction of the weather as compared to its higher resolution counterpart (first image).

Stratus-High-Res

Normal resolution radar mosaic from FIS-B (Stratus).

Stratus-4-color

Four-color radar mosaic from FIS-B (Stratus).

The reason for this may not be obvious. The data broadcast for FIS-B radar does not specifically include the raw dBZ values. Instead it uses intensity encoded values or “bins” that map to dBZ ranges as shown in the table below. Notice the wide 10 dBZ ranges for intensity encoded values of 2 and 3. Based on the RTCA standard defined in the table above, these are mapped in the ForeFlight four-color radar to green and yellow, respectively. Red is mapped to intensity encoded values of 4 and 5 with magenta mapped to 6 and 7. Because of the wide ranges as they map to the RTCA standards, the four-color radar depiction from FIS-B will use much “warmer” colors than the standard depiction.

Intensity-To-dBZ-Mapping

This table from RTCA DO-358 defines the intensity-to-dBZ mapping for FIS-B radar broadcasts. The intensity encoded values of 0 and 1 are considered background and are not displayed as a color. ForeFlight chose to use magenta for intensity encoded values of 7.

Keep in mind that the four-color radar mosaic is a low resolution depiction and will not emphasize storm characteristics like you may see with the Internet radar. This is especially true for the initial evolution of convective cells.

New International Forecast Weather Imagery Available in ForeFlight

Good news for our international customers and flight planners – ForeFlight’s Imagery view now provides a greatly expanded collection of international forecast and weather products, covering South America, Europe, and the Atlantic and Pacific oceans, in addition to the Canadian and Mexican imagery that has been available. Products include precipitation and cloud cover, temperature and wind for FL050 and FL180, prog charts, and SIGWX charts.

Tap the Global tab at the bottom of the menu to access the new imagery

The new imagery can be found in the Imagery view by tapping the Global tab at the bottom of the left-hand menu. Don’t forget that you can save a given product as a favorite by tapping the star in the top-right while viewing it, and tap the Send To button in the bottom-right to save it directly to your device, share it via email, or copy it to your device’s clipboard.

Tap the Send To button to save the image to your device, email, or copy it

Four Things You May Not Know About ForeFlight Lightning

The lightning layer now in ForeFlight has been switched to use a much improved lightning source called the Earth Networks Total Lightning Network (ENTLN). This is the world’s largest lightning detection network with over 1200 sensors worldwide. This is the same lightning network that has been used by the NTSB when investigating aircraft accidents. Here are four facts about the lightning displayed in ForeFlight.

#1 – The lightning depicted in ForeFlight is worldwide

It is estimated by research meteorologists that at any given moment in time, there are nearly 2,000 thunderstorms occurring around the world. This includes about 100 strikes for every second that passes. This is important since the presence of lightning is indicative of dangerous convective turbulence and the potential for low-level wind shear. Ground-based radar such as NEXRAD has a limited range and only covers a small portion of the earth. Lightning detectors, on the other hand, can sense strikes from a thunderstorm that is a thousand miles away providing coverage in regions where ground-based radar does not reach.

#2 – All forms of lightning are included

The Earth Networks lightning sensor is a wideband system. This enables the sensor to not only detect strong cloud-to-ground strikes, but detect weak in-cloud pulses as well. With a detection efficiency of nearly 95 percent, the lightning depicted in the distinct ForeFlight layer includes just about all of the natural lightning that is occurring around the world.

#3 – Radar layer includes lightning

While connected to the Internet, there are two ways to display lightning in the ForeFlight Mobile app. By default, lightning is included as part of the radar layer. So tapping on the radar layer in the dropdown menu will also overlay the latest lightning. However, it is important to understand that this lightning depiction overlaid on the radar has not been upgraded to use the new ENTLN as of yet.

To get the higher density lightning, you must tap on the Map mode button and select Lightning from the dropdown menu. This unique lightning layer is useful when also displaying the color-enhanced satellite layer. Areas of thunderstorms typically have very cold (high) cloud tops. Blue, yellow, orange and red colors on the satellite layer depict regions with cold cloud tops. However, not all cold cloud tops indicate an area of deep, moist convection (thunderstorms). So the lightning layer as an overlay is a good way to confirm where the truly nasty convection is occurring.

#4 – Latest 5 minutes of lightning are depicted

Regardless if you are viewing the lightning overlaid on the radar layer or the separate lightning layer, the age of the strikes depicted typically ranges from 3 to 8 minutes. Then, this lightning continues to age as it is cached in the app for the next five minutes. After this five minute period, the app automatically removes the older strikes and refreshes the display to include the latest strikes.

foreflight-lightning

Pilot Reports Get A Facelift

Pilot weather reports are the eyes of the skies. They are not only consumed by pilots, but they are critical data for meteorologists as discussed in this earlier blog post.  For example, SIGMETs for turbulence and icing often live and die by pilot reports. It’s rare to see a SIGMET issued for severe or extreme turbulence until pilots begin to report those conditions. As such they are an important part of any preflight briefing and are even more valuable as they trickle in over ADS-B while en route. That’s why we’ve given pilot report symbols used in ForeFlight a much needed facelift.

ForeFlight PIREPs

The new ForeFlight pilot weather report symbols help to quickly identify adverse weather along your proposed route of flight.

The hunt is over

In ForeFlight Mobile 7.5.2, we’ve significantly enhanced the way you see pilot weather reports displayed in the Map view. Prior to this release, pilot reports were loosely organized into three types, namely, turbulence, icing and sky & weather – each represented by a single pilot report symbol (chevron, snowflake and eyeball, respectively). However, this required you to tap on each and every PIREP marker to see important details such as altitude and intensity. Moreover, routine (UA) and urgent (UUA) pilot reports looked exactly the same. Now, standard pilot report symbology used in this release makes it clear as to the type of report, intensity, altitude (when known) and whether or not it’s an urgent pilot report without the need to tap on the pilot report symbol. So the hunt is over; with the added glance value, the truly nasty weather conditions reported by pilots jumps right out of the glass.

The good, the bad and the ugly

Pilots can include all sorts of things in a report, like seeing a flock of geese or even critters camping out on the runway. But reports of adverse weather (or lack thereof) of turbulence and icing are typically made through a subjective estimate of intensity. In order to enhance the glance value and minimize taps to get information, ForeFlight now uses standard pilot report symbols for turbulence and icing reports. Reports that do not contain turbulence or icing details are defaulted to use the legacy sky & weather “eyeball” symbol. These may contain reports of precipitation, cloud bases and cloud tops as well as outside air temperature and winds aloft (speed and direction).

New Icing PIREP Symbols New Turbulence PIREP Symbols

Each icing and turbulence pilot weather report is shown in the ForeFlight Map view with one of the symbols above that depict the reported intensity.  From left to right, the top row includes icing intensities of null (negative), light, moderate and severe. Also from left to right, the bottom row includes turbulence intensities of null (negative), light, moderate, severe and extreme.

Some intensity reports are “rounded up” to minimize the overall number of icons to remember. For example, you may notice in the symbols above that ForeFlight doesn’t use the official symbol for trace icing. Consequently, a report of trace icing is rounded up to use the light icing symbol. Similarly, we’re not providing a symbol for reports that straddle two intensities such as “moderate to severe.” Therefore, a “light to moderate” turbulence report will be rounded up to use the moderate turbulence symbol; a report of “moderate to severe” turbulence will be rounded up to use the severe turbulence symbol and so on.

Urgent-Report

All urgent pilot reports and reports of a severe nature will be tagged with a red badge to add increased glance value to those reports. For example, shown here is an urgent pilot weather report for severe turbulence at 8,000 ft MSL in the Florida Panhandle.

Above and beyond the different turbulence and icing symbols and to further attract your attention, urgent pilot reports in ForeFlight contain a red badge in the upper-right corner like the turbulence report shown above. These badges will typically be included on a turbulence or icing symbol for a report for severe or extreme turbulence and/or severe icing, respectively.

However, you may also see a red badge included with a weather & sky report like the one shown below. This is typically an urgent pilot report for low-level wind shear (LLWS) or mountain wave activity that did not also include any turbulence or icing details. Also, reports of hail, tornadoes, waterspouts or funnel clouds will be classified and tagged as urgent.

Sky & Weather Urgent

A red badge on a sky & weather (eyeball symbol) pilot report means that the report was tagged as urgent even though no icing or turbulence details were provided. Most of the time this means that low-level wind shear or mountain wave activity was reported by the pilot.

Altitude at a glance

If the pilot report contains a flight level (MSL altitude), this flight level is displayed below the symbol using three digits. For example, from the icing pilot report shown below, 057 is added below the symbol which identifies the reported altitude of 5,700 feet MSL.

PIREP Altitude

A light icing pilot weather report at 5,700 feet MSL (FL057).

On the other hand, when the flight level is unknown (FLUNKN) as it is in the icing pilot report below, we will just show the appropriate symbol (turbulence, icing or sky & weather) without an altitude. Even so, there may be specific altitudes reported, but you’ll have to tap on the pilot report marker to examine the raw report for those details. In this case, light rime ice was reported between 6,000 and 4,500 feet MSL, for example.

No Altitude PIREP

Flight level in this light icing report is unknown (FLUNKN). Tapping on the report reveals more details.

I see double

If the pilot reported both icing and turbulence in the same report, you will see a pair of symbols side by side like the ones shown below with the center of the symbol pair representing the actual location of the report. This pair of report symbols indicates light icing and light turbulence at 16,000 feet MSL.

Pair Of Symbols

A pair of reports means that both icing and turbulence details were provided for the altitude shown in the marker.

Spreading the wealth

To keep everything consistent you will also see these standard symbols show up when tapping on the Map with the AIR/SIGMET/CWAs layer displayed. AIRMETs for turbulence and icing are displayed with their respective moderate symbol and SIGMETs for turbulence and icing will be displayed with their respective severe symbol. For example, in the list below, it’s very simple now to see that the last item in the popover is a SIGMET for turbulence.

AIRMET/SIGMET Icons

Standard symbology is also used in the display of AIRMETs and SIGMETs for icing and turbulence.

Even though there’s now more information available at first glance, you will still want to examine the details of any relevant pilot reports by tapping on the specific markers. Like anything new, it may take a little while to get used to the new pilot report icons. But we feel that the use of standard symbology is critical for flight safety and these changes will provide less taps and a much higher glance value for determining the location and altitude of the most nasty weather being reported by pilots. Lastly, keep those pilot weather reports coming; they are important for all stakeholders in aviation safety.

 

Got Echo Tops?

While not rare, it is a pleasant surprise to see a fairly quiet radar mosaic stretching from coast to coast. Unless you are specifically looking for nasty weather, a tranquil radar usually means decent flying weather, outside of cold clouds, in most locations that are not reporting low ceilings and reduced visibility due to a radiation fog event. This also means you may not see some of the other familiar markers you’d normally expect to be displayed on the Map with the radar layer on. One of these markers that is often missing is the echo top heights.

Benign Radar

Overall, a fairly benign radar with the most significant returns in southern California.

First, let’s get one thing out of the way; echo tops are not the same as cloud tops. Cloud tops are always higher. Second, echo tops represent the mean sea level (MSL) height of the highest radar echo of 18 dBZ or greater. Third, echo tops heights are added to the NEXRAD mosaic in ForeFlight only when the echo tops consistently exceed 20,000 feet MSL. In other words, you won’t see an echo tops report of 15,000 feet, for example. So it’s understandable for customers to believe echo tops may be “missing” from the radar mosaic when the radar is fairly benign. Moreover, there may be some intense-looking echoes in various locations, even some with storm tracks and mesoscale circulations shown, but no echo top heights anywhere to be found. Let’s take a look at a recent example.

In the image above, notice that most of the U.S. is enjoying an early evening free of any significant weather. A few light echoes in southeast Arizona, some light snow in Montana and Idaho, showery precipitation in western Washington and probably the most intense area of weather in southern California. Zooming in on that area below, there are some areas with reflectivity values greater than 40 dBZ (yellow and orange) indicating moderate precipitation. But there’s not a single echo top height displayed even though there are several storm tracks identified. The storm tracks are there since the cellular structure and the relative high reflectivity of the echoes has triggered the NEXRAD algorithms to generate one. However, this algorithm is completely independent of the echo top height.

Southern-CA

Cellular returns indicate showery precipitation. A few cells have storm tracks defined, but despite their intensity, no echo tops are shown.

Despite the intensity of these cells in southern California, the echo top heights are likely below 20,000 feet. Since cloud tops are higher than echo tops, let’s examine the cloud top height in this area. The best way to determine the height of cloud tops is to examine the satellite imagery in ForeFlight like the color-enhanced infrared satellite image shown below. This satellite image shows the cloud top temperature. Notice the pale green colors within the black circle where the most significant returns are located. Using the color bar at the top of the image, these solid pale green colors equate to a cloud top temperature of about -20 degrees Celsius.

IR-Image

The color-enhanced infrared satellite image shows the temperature of the surface of the earth or temperature of the cloud tops. In this case, clouds in southern California have cloud top temperatures of -20 degrees Celsius.

Once the cloud top temperatures are known, it’s a simple process to compare this cloud top temperature against the temperatures aloft using ForeFlight. Below are the Winds and Temperatures aloft for Bakersfield near one of the more intense cells at this same time. This clearly shows at 18,000 feet MSL the temperatures were -6 degrees Fahrenheit or -21 degrees Celsius. So cloud tops in this region were definitely below 20,000 feet.

Temperature Aloft

The ForeFlight Winds and Temperatures aloft show a temperature of -6 degrees Fahrenheit (-21 degrees Celsius) at 18,000 feet MSL over Bakersfield.

If you were paying close attention to the radar loop, you may have noticed that one lone echo top height marker appears (pointed to by the red arrow below) of 201 indicating an echo top height of 20,100 feet in this cell. So when you see a lack of echo tops reported, it just may be that those tops are below 20,000 feet.

One Lone Echo Top

A single echo top height of 20,100 feet MSL did pop up on the radar loop bolstering the idea that most echo tops were below 20,000 feet.

Getting Into The Forecaster’s Head

With ForeFlight 7.5 you’ll have the ability to peer into the minds of forecasters. Yeah, I know… scary thought! No, we haven’t developed a method for mental telepathy within the app; but, we now provide access to the forecaster’s thinking about the latest set of Terminal Aerodrome Forecasts (TAFs) they recently issued. These are referred to as Area Forecast Discussions or AFDs. Let’s take a look at how these can be used in your routine flight planning.

Let’s say you are planning to fly into Charlotte Douglas International Airport (KCLT) arriving in the early afternoon around 1800 UTC and the latest terminal forecast issued at 1140 UTC shows good visibility (P6SM) with showers in the vicinity (VCSH) and a broken ceiling at 7,000 feet (BKN070) at the time of your proposed arrival. Does this worry you even a little bit? After all, high-base rain showers in the vicinity of the airport appears to be fairly harmless even for a pilot flying VFR? Actually, this should concern you – this may just be a forecast for thunder.

CLT-Terminal-Area

The red circle annotated here on the Charlotte TAC represents the 5 statute mile radius of the Charlotte Douglas Airport (KCLT) terminal area. This is the tiny region that forecasters consider when issuing a Terminal Aerodrome Forecast (TAF).

Just because you don’t see a forecast for TS, TSRA or VCTS in a TAF, doesn’t that mean you won’t see thunderstorms arriving or departing that airport. What it could mean is that the forecaster wasn’t confident enough at the time he/she issued the forecast that a thunderstorm would develop within or roll through the region referred to as the terminal area. The terminal area is the region of airspace within a 5 statute mile radius from the center of the airport’s runway complex like the one shown above for the Charlotte Douglas International Airport (KCLT). So it is common for meteorologists to use showers in the vicinity (VCSH) or rain showers (SHRA) as a placeholder for thunder when forecaster confidence is low.

Here’s the problem

The forecaster doesn’t have an obvious way to quantify his/her uncertainty in the actual body of the coded TAF. Quantifying uncertainty is paramount when constructing any forecast (especially one for thunderstorms) and is usually done with a probabilistic approach – you know, a chance of this or a chance of that.

What about the PROB group that you may have seen in a TAF? Sure, that would work, but NWS directives state that a PROB30 group can’t appear within the first nine hours of the terminal forecast. By the way, the NWS only uses PROB30 groups; although you may see PROB40 in TAFs when flying to other countries. So back to the issue – how does a pilot know that showers in the vicinity is a placeholder for thunder in the TAF issued for Charlotte Douglas International Airport?

AFDs to the rescue

First, AFD doesn’t stand for Airport/Facility Directory as you may have thought. It’s called an Area Forecast Discussion. Second, it’s not a discussion about the aviation Area Forecast (FA) issued by meteorologists at the Aviation Weather Center. Are you thoroughly confused yet? The AFD is one of the most commonly accessed products on NWS Web sites, however, very few pilots have even heard of them. Now they are available for you to read beginning to end in the ForeFlight Mobile app!

County Warning Areas

A map of the County Warning Areas (CWAs) across the United States. There is an Area Forecast Discussion (AFD) generated for each one of these CWAs.

The AFD is a discussion that is written by the same forecasters that issue the TAFs. Every NWS local Weather Forecast Office (WFO) throughout the United States issues terminal forecasts for airports that appear within their County Warning Area (CWA), hence the term Area Forecast Discussion. After TAF issuance, meteorologists are required to update the AFD with a plain english discussion explaining their thoughts behind the forecast which allows them a plethora of ways to quantify their uncertainty. AFDs were originally designed as technical discussions to enhance collaboration among NWS forecast offices and to convey uncertainty to a specialized audience. So the language can be quite technical at times, but still highly useful to pilots. Let’s get back to your flight into Charlotte.

The GSP AFD has some clues

For example, the AFD associated with this TAF for the Charlotte Douglas Airport is written by a forecaster located at the Greenville-Spartanburg WFO (GSP) in Greer, South Carolina. Here’s the pertinent part of the discussion that morning:

AVIATION /16Z TUESDAY THROUGH SATURDAY/…

AT KCLT…LITTLE CHANGE FROM 06 UTC PACKAGE AS A WEST WIND LESS THAN 8 KTS UNDER MOSTLY CLEAR SKIES WILL CONTINUE THROUGH MID-MORNING. EXPECT INCREASING WSW WINDS WITH LOW AMPLITUDE GUST POTENTIAL BY MIDDAY AND PERHAPS PERIODS OF VFR CEILINGS THROUGH THE AFTERNOON. SCATTERED SHOWERS AND A PERHAPS A THUNDERSTORM…ARE EXPECTED ACROSS THE NORTH CAROLINA PIEDMONT FROM THE AFTERNOON UNTIL EARLY EVENING AND WILL CARRY VCSH FOR NOW TO COVER THAT THREAT. DEEP CONVECTIVE ACTIVITY WILL DIMINISH BY MID-EVENING WHEN A WIND SHIFT TO NORTHWEST IS EXPECTED.

As stated in this AFD text that is highlighted above, the forecaster opted to use showers in the vicinity (VCSH) to cover the threat for thunder in the North Carolina Piedmont region where KCLT is located. Most pilots don’t realize or appreciate that showery precipitation is actually a convective process. So forecasters will often use showers as a placeholder when confidence of thunder is low. This is not to say that every forecast for showers is used in this way, but that is a common way the forecaster quantifies his/her uncertainty for convective events such as this.

For whatever reason, the forecaster wasn’t quite confident enough to impart a little meteorological risk and add thunderstorms to the Charlotte TAF. This is in part due to the relatively small size of the terminal area. If the thunderstorms in the area are anticipated to be of a scattered nature (as it was on this day), they will often omit a forecast for thunder until they are more certain thunderstorms will indeed impact the terminal area. In some situations they may use showers to hint that convection will be in the area without adding TSRA or VCTS to the forecast. As the convective weather event evolves and certainty increases, they will issue an amended forecast to add thunder. But these details are not part of the official forecast. For better or for worse, they are buried in the AFD. The AFD is the place where the forecaster can freely quantify his/her uncertainty and provide some background on why the forecast is constructed the way it is.

Moreover, meteorologists at the local weather forecast offices that issue forecasts for high impact terminal areas such as Charlotte Douglas have a fair amount of outside pressure from the airlines to avoid adding thunder to the forecast unless convection is fairly certain. A forecast for thunder at the proposed time of arrival means the airlines must file an alternate and carry extra fuel to get to that alternate.

So what actually occurred at Charlotte Douglas?

Did thunder ever affect the Charlotte terminal area? Yes, at 1813 UTC the observation (METAR) included a report for a thunderstorm at the airport as shown below.

KCLT 271813Z 07003KT 10SM TS SCT040CB BKN090 BKN200 16/09 A2956
RMK AO2 TSB13 OCNL LTGIC TS SE-SW-W MOVG E CB NW-N MOVG E

But, it wasn’t until 1739 UTC (a mere 34 minutes earlier) that the forecaster amended the TAF to include a forecast for light rain and thunder as shown below.  Some pilots might opine that the TAF issued at 1140 UTC was a bad forecast. However, given the scattered nature of the convection on this day (read uncertainty) the placeholder of showers in the vicinity was the method used to indicate the risk of thunder. The AFD was the place the forecaster documented this important piece of information.

KCLT 271739Z 2718/2818 26008G18KT 6SM -TSRA BR BKN045 OVC070CB
TEMPO 2718/2720 25010G20KT 5SM -TSRA BR SCT030 OVC050CB…

The AFD format

The raw AFD doesn’t have a rigid syntactical or semantic format that forecasters must follow. Moreover, that format may differ from one forecast office to the next. That’s both good and bad. At ForeFlight we do make an attempt to visually separate the discussion into sections with a header where it is possible. Although you may find that some WFOs do a better job than others sticking to a common format as described below; so don’t count on perfection with the AFDs.

AFD Synopsis

Most Area Forecast Discussions (AFDs) will contain a synopsis section followed by a near-, short-, and long-term discussion. Simply scroll the window down with your finger or stylus to see the rest.

Each AFD will typically start out with a SYNOPSIS section (as shown above) followed by a NEAR TERM, SHORT TERM and LONG TERM discussion. This is the accepted format for the NWS Eastern Region. In other regions you may just see one big DISCUSSION section. While not specific to aviation, these sections are important to read and often may describe the “big picture” and point out many clues and trends as to what adverse weather might occur over the next several hours or even several days. Of the most interest to pilots, every AFD will also include an AVIATION section like the one shown below. This is the section where the forecaster discusses the TAFs and aviation-specific concerns. Lastly, in some parts of the country you may find a separate section that discusses fire dangers and marine weather.

AFD Aviation

Every AFD should have an aviation section. The AFD is automatically scrolled to this section when first viewed. Also notice that key words or phrases may be highlighted in red to point out the discussion of various adverse weather elements.

While most of the sections in the AFD are word-wrapped, you may see some tabular sections like the confidence table shown below. In order to preserve the columnar format within this section, you can scroll these sections left and right with your finger or stylus (notice the horizontal scroll bar below this table).

AFD Tabular

Some sections in the Area Forecast Discussion (AFD) are tabular. In these cases, the section can be scrolled to the right to see the remaining part of the table.

Finding the AFD in ForeFlight

The AFD is available to all ForeFlight subscribers and to locate it in the app is as simple as finding a METAR or TAF. On the Map, bring up any airport-specific layer such as Flight Category and tap on the airport marker. Next, tap the Forecast tab at the bottom of the pop-over window then tap on the new Discussion button at the top to reveal the AFD for that airport’s CWA as shown below. The Discussion button will be located to the right of the MOS button.

AFD Location

The Area Forecast Discussion (AFD) is located under the Forecast tab on the station popover right next to the MOS button.

You can also view AFDs in the Airports view. With the airport of interest displayed, tap on the Weather tab, then tap on Forecast Discussion as shown below. However, be careful not to confuse this with the Airport/Facility Directory (A/FD) tab.

AFD Airports view

The Area Forecast Discussion (AFD) can be shown within the Airports view similar to the way METARs, TAFs and MOS are displayed.

The Fine Print

When tapping on the Discussion button in the pop-over window, the AFD is auto-scrolled to the Aviation section. From there you can scroll up or down to read the rest of the forecast discussion. Similarly in the Airports view, the Aviation section is also displayed first by tapping on Forecast Discussion under the Weather tab. Tapping on Forecast Discussion again, will position it to the beginning of the discussion text.

While most of the discussion is in plain english, there will be times where abbreviations and acronyms will rear their ugly head. We’ve made an honest attempt to decode most (but not all) of these within the text. Moreover, you will see some words and phrases highlighted in red. Hopefully these will grab your attention since they sometimes point out discussion that includes more extreme adverse weather.

Mind the limitations

AFDs are only available for airports within the United States (including Hawaii and Alaska). So selecting any airport within the U.S. should result in retrieving the latest AFD based on the CWA that airport is located within. Consequently, airports outside of the U.S. won’t have a Discussion button on the pop-over or under the weather tab on the Airports view. Occasionally, the latest AFD may not be available and you’ll see a “No forecast discussion” response. This is a very rare occurrence, but it may happen from time to time.

While some forecasters put a fair amount of time and detail describing their thoughts, not all AFDs will have details you might be hoping to learn. The AFD isn’t their highest priority; when the weather is busy the AFDs will often get the short end of the stick. That same forecaster may have to help with radar and issuing severe thunderstorm and tornado warnings on a busy convective day, for example.

In the end, expect the AFDs to provide a complementary product to the TAFs. If you are not reading the AFDs, you are only getting half the story.

New Graphical Preflight Briefing, Track Log and Weather Upgrades in ForeFlight 7.4

For years, pilots have endured a cryptic, wall-of-text preflight briefing. With ForeFlight Mobile 7.4, we are thrilled to introduce ForeFlight Briefing—a graphical, translated, interactive briefing that helps you better visualize weather and related flight information along your proposed route. This release also delivers an enhanced AIR/SIGMETs map layer and new Track Log capabilities that allow you to automatically record your flights.

You Can Brief Clearly Now With ForeFlight Briefing

ForeFlight Briefing is a standard briefing with content derived from approved government sources. It includes all the elements of a standard preflight briefing prescribed by the FAA—adverse conditions, synopsis, current conditions, enroute and destination forecasts, NOTAMs, and more—delivered in a visually elegant design for enhanced readability. With this next generation briefing format, we believe you will enjoy and get more from the preflight briefing.

ForeFlight Briefing is seamlessly integrated into the ForeFlight Mobile app and is presented in clearly organized sections, making it simple to tap through each element of the briefing in a logical sequence. Translated and raw text options are available, as well as full-color graphics, which help you better understand and consume briefing information.

ForeFlight Briefing organized into logical sections

Some helpful aspects of the new briefing include color-coding and notations to indicate if an advisory will be active or inactive during or near your passing time:

ForeFlight Briefing with active and inactive AIRMET alertAlso, colored dots used in conjunction with METARs and TAFs give you an at-a-glance view of current and forecast weather. In the screen shot above, green represents VFR, blue is marginal VFR, red is IFR, and magenta is low IFR.

In the TAF view, color-coding is again used to indicate the forecast flight category. Based on your planned departure time and aircraft profile, your passing time at each station is automatically calculated and plotted on the TAF:

ForeFlight Briefing on the iPad and iPhoneThe briefing is mobile and portable—once the briefing is retrieved, you do not need an Internet connection to access it again on the go. In addition, after you file your flight plan you can click the link in your confirmation email to view the briefing on any web browser.

In addition, ForeFlight Briefings are timestamped and stored on your iPad and iPhone, and in the ForeFlight cloud, to record that you obtained weather and pertinent NOTAMs in compliant manner with 14 CFR 91.103(a) preflight action.

ForeFlight Briefing is available to all customers with ForeFlight Mobile version 7.4 on both the iPad and iPhone. Customers with 7.4 installed will be automatically given the opportunity to use the new format the next time they brief a planned flight.

For more information visit foreflight.com/briefing/.

Global SIGMETs, New Graphical Center Weather Advisories

The refreshed AIR/SIGMET/CWAs Map layer now includes graphical Center Weather Advisories (CWAs) alongside AIRMETs and SIGMETs, giving you a better picture of current conditions. SIGMETs are also expanded to include global coverage.

Refreshed AIR/SIGMET/CWA map layer

A new interactive filter on this layer helps you single out adverse condition advisories based on type (icing, turbulence, IFR conditions, and thunderstorms), allowing you to declutter and get straight to the information you want to know:

AIR/SIGMET/CWA layer filter

Scott Dennstaedt, our in-house Weather Scientist, has written this blog post and this one to provide more insight on how to use these helpful weather resources in your everyday flight planning.

Capture Every Flight—Automatically

Have you ever been half-an-hour into a flight and realized you forgot to tap the Track Log record button? Now you don’t have to remember! With 7.4, we’ve made it easier than ever to record your flights.

Track Log shown in Google Earth.

Track Log shown in Google Earth.

Track Logs can automatically start recording when you take off and, after touchdown, automatically stop recording—ensuring that every flight is captured for your post-flight debrief. When you get back to Wi-Fi, Track Logs are also automatically uploaded to the ForeFlight cloud for safekeeping and for easy access from your other devices.

The Track Log includes your taxi time so you can have a complete record of your time in the cockpit — on and off the ground.

You can control the auto-record function in the app settings:
Track Log record settings

(Please note that Stratus Track Logs do not currently auto-upload.)

Apple iOS 9 Spotlight Search

ForeFlight Mobile 7.4 supports Spotlight Search, Apple’s smart search feature, which now displays relevant airport results from inside ForeFlight Mobile right on your device’s Home page.

ForeFlight and Apple Spotlight Search

To access Spotlight Search, swipe from left to right on the Home page of your iPad or iPhone. Begin typing an airport name, identifier, or city name and results from ForeFlight Mobile populate the search results list. Tap the desired airport search result and ForeFlight Mobile opens directly to that location in the Airports view. To continue searching, tap “Back to Search” in the upper left corner of the screen to return to the Spotlight Search view. Spotlight Search is available on iPhone 5 and up, all iPad Air models, and iPad Mini 2 and up.

App-Store-icon

ForeFlight Mobile 7.4 is a free update available on the App Store.

Weather On The Front Lines

If you surveyed a group of general aviation pilots, it would probably not surprise you to learn that Center Weather Advisories are not a weather source that pilots use very frequently when planning a flight. They have always been included within the ForeFlight Mobile app by tapping the Brief button under File & Brief. But this standard briefing only provides the advisory in raw text form—unless of course you are using the new and improved ForeFlight Briefing where it is also displayed graphically. In ForeFlight Mobile 7.4, Center Weather Advisories are now depicted graphically within the existing AIR/SIGMET layer on the Map view making them even more useful.

In-flight advisory

Center Weather Advisories, or CWAs, are the “front lines” of aviation weather in the U.S. for adverse weather such as low IFR conditions, thunderstorms, icing, and turbulence. While they smell a lot like AIRMETs and SIGMETs, they are more of an in-flight advisory about current conditions than they are a planning tool or forecast. Therefore, it’s critical to look for these while en route to your destination and just before you close the door to depart. Now is a good time to mention that CWAs are not part of the ADS-B broadcast so you will not receive them while connected to a Stratus.

Center centric

CWAs are issued by highly trained meteorologists at the Center Weather Service Units (CWSUs) located at the various Air Route Traffic Control Centers (ARTCCs) pictured below.

ARTCC Map

A map of the Air Route Traffic Control Center (ARTCC) boundaries in the U.S. Each ARTCC has a Center Weather Service Unit (CWSU) staffed by meteorologists that are responsible for issuing Center Weather Advisories (CWAs) for their respective ARTCC area.

CWAs are issued to warn pilots of the following in-flight weather hazards:

  • Conditions meeting or expecting to meet convective SIGMET criteria
  • Moderate or greater airframe icing
  • Moderate or greater turbulence
  • Heavy precipitation
  • Freezing precipitation
  • Conditions at or approaching Low IFR
  • Sustained surface winds/gusts > 30 knots
  • Non-convective low level wind shear below 2,000 feet AGL
  • Volcanic ash, dust storms, or sandstorms

Short lead time

Unlike their AIRMET counterpart, CWAs are not routinely issued and have no defined schedule. Moreover, they have a very short lead time since they are issued on an as-needed basis. So it’s not unusual to see a CWA issued at 20 minutes past the hour to describe adverse weather that has evolved very rapidly. Once issued, CWAs are valid for two hours or less. If conditions are anticipated to persist beyond two hours, it will be indicated in the last line of the CWA text. As mentioned earlier, CWAs are not as valuable of a preflight planning tool because of its short lead time and duration. They tend to pop up as adverse weather evolves or develops throughout the U.S. and along its coastal waters.

Complementary guidance to other advisories

Forecasters at the CWSUs have a fair amount of latitude when issuing a CWA. Conditions do not have to meet national in-flight advisory criteria in terms of intensity or areal coverage. For example, unlike convective SIGMETs, CWAs for convection can be issued before thunderstorms have formed. That is, they can describe a broad area of towering cumulus or showery precipitation that is trending toward an aviation hazard within the next two hours especially in regions that may affect flow into or out of busy airspace. Convective SIGMETs issued by forecasters at the Aviation Weather Center (AWC) are more of a NOWcast that warn pilots about active areas of thunderstorms that have already met specific hazard criteria.

A good example of its complementary nature is a CWA for low IFR conditions. An AIRMET for IFR conditions is primarily directed at pilots flying under visual flight rules (VFR). It describes an area that may experience a ceiling and/or visibility below VFR minimums. However, what if a portion of the AIRMET region is also plagued with persistent low IFR conditions? This would be critical information for all pilots including those flying under instrument flight rules (IFR). As shown below, given the number of stations reporting low IFR conditions (magenta markers) within the AIRMET region, the Denver CWSU issued a CWA for ceilings at or below 500 feet and visibility at or below 1/2 statute miles.

Low IFR CWA

This Center Weather Advisory (CWA) was issued for ceilings at or below 500 feet and visibilities at or below 1/2 statute mile that were occurring within an existing AIRMET for IFR conditions.

While CWAs can be issued at any time, they are generally coordinated with other agencies within NOAA to ensure meteorological consistency between products. This includes meteorologists at the AWC who are responsible for issuing the area forecast, AIRMETs, SIGMETs and convective SIGMETs. It’s pretty typical for the meteorologist at the CWSU to have a brief phone conversation with the appropriate meteorologist at the AWC before issuing a new CWA.

Finding CWAs in ForeFlight

The CWA layer can be displayed from the Map view in ForeFlight Mobile 7.4. Simply tap the Map mode button in the upper left and select AIR/SIGMET/CWAs from the menu as shown below:

CWA Menu

Center Weather Advisories (CWAs) can be selected from tapping the mode button and selecting AIR/SIGMET/CWAs from that menu.

Once the layer has been selected you will see CWAs depicted on the ForeFlight map view as cyan-colored polygons regardless of the hazard type. In most cases, these areas will be smaller in size than an AIRMET or SIGMET because of their complementary nature and short duration. To see the associated uncoded text of the CWA, simply tap on the polygon in the same way that you view the uncoded text for AIRMETs and SIGMETs. Be sure to always read the text of the CWA since it will have additional details about the flight conditions such as the altitudes affected and an indication of whether or not conditions are expected to improve or persist beyond the valid time.

Buttons

When AIR/SIGMET/CWAs are selected, the four buttons at the bottom of the Map allow you to filter advisories according to hazard type.

Lastly, given that CWAs are a complementary product to AIRMETs, SIGMETs and convective SIGMETs, with ForeFlight Mobile 7.4 you can overlay them with other advisories. Tapping on the buttons at the bottom labeled Ice, Turb, IFR and TS, will permit you to add or remove CWAs from the Map based on hazard type. In this example above, only IFR hazards are selected which includes AIRMETs for IFR conditions and mountain obscuration as well as a single CWA for low IFR conditions captured by the cyan-colored polygon. Any advisories for icing, turbulence and convection (if any) have been filtered from the Map.

Weather Without Borders

With ForeFlight Mobile 7.4, SIGMETs issued beyond the U.S. border can now be displayed. These International SIGMETs are advisories that cover a wide range of hazards including convection (thunderstorms), severe turbulence, severe icing, tropical cyclone and volcanic ash just to name a few. In most cases these are displayed on the ForeFlight Map view as polygons similar to the way domestic AIRMETs, SIGMETs and convective SIGMETs are depicted. To help with all of these new advisories, we’ve also added the ability to filter this layer by the type of hazard.

The whole FIR and nothing but the FIR

Unlike advisories issued by forecasters in the U.S., International SIGMETs are not always well defined by the source. Occasionally the origin country may not provide the points that define the advisory area. For those situations, the entire Flight Information Region (FIR) is displayed on the Map as is shown below for a hazard within the Mexican FIR.

Entire FIR

When the source of the SIGMET isn’t specific about the exact location of the hazard, the entire FIR may be outlined in red.

Unspecified conditions

Similarly, when tapping on a SIGMET polygon, you may see “Unspecified Conditions” displayed in the title of the popover as shown below. This means the source of the advisory did not specify the details of the type of hazard. While ForeFlight will make an attempt to determine the hazard by parsing the raw text, there’s no guarantee we will be able to make that determination in every case. In these situations it’s strongly encouraged to review the raw text of the SIGMET for the details.

Unspecified Conditions

In some cases the type of adverse conditions are not specifically provided by the source government. For those situations, Unspecified Conditions will be shown. You are encouraged to read the raw text for those details.

No more clutter

Another feature added to ForeFlight Mobile 7.4 is the ability to filter the AIR/SIGMET/CWAs layer by hazard type. When this layer is displayed, you’ll notice four buttons at the bottom of the Map view labeled Ice, Turb, IFR and TS representing hazards associated with airframe icing, turbulence, IFR conditions and convection, respectively. Tapping on any of these buttons will add or remove advisories for that hazard type from the Map. For example, the Turb, IFR and TS hazards have been filtered with only the Ice hazard displayed as shown below. Please note that these selections are preserved. Therefore, if you’ve removed the layer from the Map or closed the app, the next time you view the AIR/SIGMET/CWAs layer on your device, the hazard selections you made earlier will be restored.

AIR-SIGMET-Filters

When the AIR/SIGMET/CWA layer is active, use the buttons at the bottom to hide or display the advisories by hazard type.

The only hazards that are never filtered are those SIGMETs issued for tropical cyclones, radioactive cloud or volcanic ash like the one shown below. These SIGMETs often persist for days or even weeks at a time once they are issued.

Volcanic-Ash-SIGMET

Not all hazards can be filtered. These include volcanic ash, radioactive cloud and tropical cyclone advisories.