G-AIRMETs in ForeFlight

In 2008 the FAA’s Aviation Weather Center began phasing out AIRMETs (Airman’s Meteorological Information) in favor of G-AIRMETs (Graphical AIRMETs). In anticipation of the switch to exclusively using G-AIRMETs, ForeFlight recently made the change to displaying G-AIRMETs in the AIR/SIGMETs/CWAs layer in the Maps view. 

AIRMETs and G-AIRMETs have their differences, but since they are made from the same data, they are consistent in their messages. Why are G-AIRMETs used and how does that affect pilots using ForeFlight? 

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Most pilots will notice that G-AIRMETs in ForeFlight don’t contain the same text that is usually associated with AIRMETs. That text usually indicated geographical information for the AIRMET and since G-AIRMETs are graphically depicted AIRMETs, the additional text is not needed. In the past, ForeFlight would parse this geographical description to display it on the map the same way we display G-AIRMETs, resulting in no noticeable change to pilots. 

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Additionally, AIRMETs are limited by a character count, making it difficult for forecasters to fully convey weather conditions. Some forecasters have been forced to combine geographical areas of the forecast or cut out sections of the text to get their message through the FAA system. 

AIRMETs provide geographic data using VORs to describe the area of weather conditions, while G-AIRMETs use lat/long coordinates and can use many more points to describe an area (due to the lack of character limit), giving pilots a more accurate geographical depiction of weather. 

The FAA issues G-AIRMETs in 3 hour blocks and AIRMETs in 6 hour blocks that blend the data into one image. This means that multiple G-AIRMETs issued for different times could be turned into a single AIRMET lasting for much longer than required, possibly preventing pilots from flying in an area that would be otherwise cleared with G-AIRMETs.

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Since G-AIRMETs use smaller time increments, ForeFlight provides a time slider at the bottom of the Maps view when you enable the AIR/SIGMETs/CWA layer. Scrub the time slider to view G-AIRMETs that will be active at different times in the future. If you have another time-based weather layer turned on, ForeFlight will replace the time slider increments with the other layer, letting you view G-AIRMETs that are active at the time of the other layer’s frame. If you combine the AIR/SIGMETs/CWA layer with a longer term forecast layer like Surface Analysis or Icing, you’ll find that the G-AIRMETs will disappear if you move the slider past the expiration time of the final active G-AIRMET.  

Weather in Profile View, Overheat Alerts, and More in ForeFlight’s 12.6 Release.

ForeFlight 12.6 includes weather in Profile View, iPad/iPhone Overheat Alerts, additional Internet Traffic details, and more.

Weather in Profile view

ForeFlight’s Profile View includes selectable Icing and Turbulence forecast layers, providing a cross-section of weather in addition to terrain, obstacles, and airspace along your route. Icing and Turbulence in Profile View are included in ForeFlight’s Performance Plus and Business Performance subscription plans.

Create a route on the Maps view then tap Profile in the bottom-right to open Profile View. Profile View shows a side-on view of your route in relation to terrain, obstacles, airspace, and now weather.

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One major change to Profile is the addition of a layer selector that allows you to toggle different layers within Profile View, including Airspace, US or Global Icing, and US or Global Turbulence. Profile View uses the same color scales as the overhead map to depict varying intensities for each layer at multiple altitudes in relation to your route line.

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Tap the Profile Layer Selector, and tap a weather layer to display it in Profile. In addition to Airspace, Profile View can display one Icing layer and one Turbulence layer simultaneously. Each selected layer shows how long ago the current forecast data was issued. All four weather layers use the same data as their corresponding layers on the overhead map, providing multiple perspectives of a single forecast. ADS-B, XM, and military Icing and Turbulence layers are not supported in Profile View.

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Rather than using a time slider to show different forecast periods like the overhead map, Profile View combines any forecast periods that will be active during your flight into one seamless display. The waypoint markers in Profile View include estimated crossing times, allowing you to easily determine the forecast period shown at each waypoint and view the same forecast on the overhead map. Changing the selected aircraft or performance profile will display different icing and turbulence data in Profile view based on the route’s new enroute time.

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If a portion of your route’s planned active time lies beyond a weather layer’s forecast range, Profile View will display a hatch pattern to indicate where data is not available (visible on the right side of the screenshots below). It will also provide warnings letting you know which forecast data is not available for some or all of your flight. This hatching also appears if you disconnect from the internet without downloading weather data via Pack. With the data downloaded, Profile view’s inflight mode also supports all four weather layers, allowing you to view current and future forecast periods in relation to your current altitude and heading.

Another way to use Profile View with or without a route entered is by placing two fingers on the overhead map to bring up the Ruler, then move your fingers to reposition it. Using the Ruler with Profile View provides a cross-section of the terrain, obstacles, airspace, and selected weather layers at the Ruler’s current position. Profile View shows only the current forecast period for Icing and Turbulence layers when using the Ruler.

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Overheat Alerts

ForeFlight warns you if your iPad or iPhone is in danger of overheating with a prominent visual and audible alert, allowing you to take steps to cool the device and potentially avert a shutdown during a flight.

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Manage all alerts in ForeFlight in More > Settings > Alerts. The alert is triggered when ForeFlight detects that your device is dangerously hot and at risk of overheating and shutting down. If your device heats up too quickly, your iPad or iPhone may still overheat and shut down before ForeFlight can display the alert. The alert will not sound more than once per hour, even if your device returns to a high-temperature state after initially cooling down.

Removing the iPad or iPhone from direct sunlight and turning an air vent towards it are the best ways to quickly cool it down. Other ways you can cool your device down include removing your device from its case, closing unused apps, and unplugging it from its charging cable. A number of powered cases that cool the iPad using fans are also available from Sporty’s and other vendors. 

Additional Internet Traffic Details

ForeFlight’s Internet Traffic layer provides additional information for aircraft markers, including its expanded call sign, ETA, departure, and destination if available.

Turn on Internet Traffic in the layer selector in the Maps view. Tap on any aircraft marker to view a popup with information about that aircraft.

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The popups for most aircraft on IFR flight plans show the departure and destination airports and filed ETA, while many aircraft on VFR flights provide only the departure airport. Some traffic targets provide no route details. If an aircraft is using a call sign, the popup will show its expanded name in most cases. Internet Traffic targets with blocked tail numbers will not report any route or call sign information.

Learn more about Internet Traffic here.

High-Resolution Basemap Improvements

ForeFlight’s High Resolution Basemap received some improvements to mountain peaks and passes. The Basemap identifies mountain peaks using a small triangle icon in place of the previous dot icon. The Basemap also displays many additional U.S. mountain passes with their associated elevations.

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Download the High Resolution Basemap in More > Downloads > Download Settings. Turn on mountain peaks and passes in Map Settings (cog button on the Maps view) > Terrain > Peaks, Passes, and Cables.

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You can also change the size of the icons by turning on the Aeronautical Map in the layer selector, and adjusting the text size slider in Map Settings.

Y/Z Filing in Canada

Customers flying in Canada can now file flight plans under Y or Z flight rules through ForeFlight. Since these flight rules both include VFR portions, certain fields in the flight plan form that are required for Canadian VFR flights are also required for Y and Z flights, including Undercarriage, ELT, Arrival Report, and more. Cross-border flights from Canada to the U.S. or to airspace delegated to the U.S. by Canada for ATC traffic purposes do not support Y/Z flight rules.

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ForeFlight Adds New Forecast Graphics to Imagery View

We recently added two new collections of graphical forecasts to the Imagery view on mobile and web: Graphical Aviation Forecasts for cloud cover and surface conditions, and Ceiling and Visibility Analysis graphics.

Graphical Aviation Forecasts

While the Graphical Aviation Forecasts were already available as part of ForeFlight’s Graphical HTML Briefing, they are now even more accessible alongside ForeFlight’s other graphical weather imagery. The new cloud and surface forecasts replace the GFS MOS ceiling and visibility graphical forecast products, which NOAA discontinued in mid-December 2019. The GFS MOS textual products for ceiling and visibility are still available on NOAA’s site and in ForeFlight’s MOS airport weather tab.

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The Graphical Aviation Forecasts for both cloud cover and surface conditions are provided for CONUS and nine additional regions: Northeast, East, Southeast, North Central, Central, South Central, Northwest, West, and Southwest. Each region and forecast type includes graphics for six forecast periods: 3 HR, 6 HR, 9 HR, 12 HR, 15 HR, and 18 HR. Forecasts are typically updated every 3 hours.

The Cloud Coverage product depicts not only the degree of cloud coverage (few, scattered, broken, or overcast), but also cloud top altitudes and icing or mountain obscuration AIRMETs.

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The Surface product depicts even more, showing obscuration hazards and types (haze, fog, smoke, or dust/sand), weather conditions with color-coded probabilities (rain, snow, mix, or ice), thunderstorm probabilities, surface visibility, IFR or surface wind AIRMETs, and surface wind barbs with gust speeds indicated by red extensions on each barb’s tail.

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Ceiling and Visibility Analysis

The Ceiling and Visibility Analysis collection provides three graphics depicting Flight Category, Visibility, and Ceiling information for CONUS and 18 major subdivisions, each named after a city in each region. 

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These detailed graphics replace the single “Weather Depiction” chart that was previously available in the National > Featured section. Visit this page hosted by NOAA for information about the different symbols used in these forecast graphics.

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As with other graphics in the Imagery view, you can share, copy, or download the new forecast products using the Send To menu in the bottom-right while viewing them.

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A Closer Look at Global Icing, Turbulence, and Surface Analysis Map Layers

Available with ForeFlight Mobile 9.4, five new weather layers bring global Icing, Turbulence and surface pressure data to the map, with detailed Surface Analysis available to much of North America. These weather products significantly enhance local and global flight planning and your weather decision-making abilities. In addition, the recently introduced time slider provides frame-by-frame control over animation of the new weather layers.

The new layers are available both on mobile and web with the Pro Plus and Performance Plus subscription plans, as well as Business Performance, MFB Pro, and MFB Performance. If you don’t have one of those subscription plans, click here to upgrade and unlock these powerful weather layers.

Layer Animation Time Slider

The animation Time Slider tool provides better control over weather layer animation, as well as more clarity on the age of the weather product you are viewing. The slider automatically displays when you select any Radar, Satellite, Icing, or Turbulence layer.

Weather Layer Time Slider

In addition to the familiar play/pause button, the Time Slider allows frame-by-frame control over the animation. The slider’s position on the time scale indicates the valid time for the currently displayed weather graphic. Tapping to the right of the slider head advances the layer by one time step, while tapping to the left of the slider head retreats the layer by one time step. Alternatively, tap-hold and move the slider head left and right to manually control animation speed and enable back and forth (rocking) animation, a useful capability when analyzing local storm cell changes on radar.

The time scale changes as appropriate for each weather product displayed. Forecast-based weather layers, such as the Icing and Turbulence layers, use a white vertical bar to indicate the present time, splitting the time slider into two parts: forecasts that are valid for the past (gray line) and for the future (white line).

Products that indicate past information only, such as the radar and satellite layers, are presented with a gray time scale with the product age, relative to the current time, displayed with each frame. The absolute time is displayed in a callout with each frame as you manually scrub left or right, as well as to the left of the time scale.

Providing full manual control over the weather layer animation and easily reading relative age and absolute time for each weather product frame provides better insight to how the weather is trending.

Surface Analysis

The Surface Analysis layer adds a global surface pressure overlay, displaying isobar lines and associated pressure values in millibars. For much of North America, the isobar lines are complemented with depictions of surface fronts, troughs, and high/low pressure center markers. Besides displaying the current surface analysis, the forecasted surface analysis can be viewed for up to two days into the future using the Time Slider.

The Surface Analysis product and its forecast is a collaboration between multiple weather centers and is primarily based on the National Weather Service Global Forecast System (GFS) and the North American Mesoscale (NAM) models, with additional guidance from the European ECMWF and the United Kingdom’s UKMET models. Surface features (fronts, troughs, pressure centers) are analyzed manually by a NWS meteorologist, and are therefore only available for the North America region.

Surface Analysis features follow the standard depiction convention as outlined in the table below:

View global isobars and more detailed weather features for the U.S.

Icing

Icing severity data for the United States has been available in the ForeFlight Mobile Imagery view since 2015. Now, icing severity is available as a dynamic weather layer in the Maps view in ForeFlight Mobile and on the web. And not just for the US, but for the entire world.

You will now see two icing products in the Maps view layer selector: Icing (US) and Icing (Global). Both serve the same purpose, but are based on different weather models.

For the US coverage, the Forecast Icing Product (FIP) is a Numerical Weather Prediction model that employs a 20km grid in the horizontal and a 1000 ft grid in the vertical (from 3000’ to FL450) to calculate icing severity and the potential for SLD (supercooled large droplets). The FIP model is run hourly and forecasts are available out to 18 hours.

For a fast analysis of conditions at each altitude, you can quickly scrub between altitudes using the Altitude Slider in the lower right corner of the Maps view. The Altitude Slider is also available on the Turbulence layer.

Altitude Slider

Altitude Slider

Please note that SLD threat is currently only available to customers flying with the SiriusXM SXAR1 aviation receiver and who are subscribed to the SiriusXM Pilot for ForeFlight plan. SLD threats are depicted with red squares.

The Global Icing product is based on the Global Forecast System (GFS) weather model with a coarser horizontal and vertical grid and is run four times per day (every 6 hours). Global Icing forecasts in ForeFlight are available out to 24 hours.

Because of the coarser grid, as well as the less-frequent model runs of the GFS, it’s worth comparing the two icing depictions side-by-side. The difference in horizontal resolution and model update frequency between the US icing layer (left) and the global icing layer (right) is evident. When operating within the limits of the US icing model coverage area, the US icing layer should be referenced instead of the global layer to take advantage of its frequent updates and finer horizontal and vertical grid resolution.

Regardless of whether you have US or global icing selected, each layer uses the same color scale to depict conditions of no icing, light, moderate and heavy icing, as shown in the legend below:

Icing intensity is based on how long it would take for ice to build up on an airfoil

It’s important to note that the icing severity is roughly based on the accretion rate of ice on an airplane. The severity levels are defined by how long it would take for ¼ inch (65mm) of ice to build up on an airfoil. Time ranges are given for each level because the build-up rate depends on variables like airfoil properties, airspeed, and atmospheric conditions.

Since the icing forecasts are produced with no human modifications, they are intended for flight planning purposes only and should always be used in combination with AIRMETs, SIGMETs and PIREPs.

Turbulence

Similar to the Icing map layer, there are two new Turbulence map layers, one for the United States and the other for Global coverage.

The US turbulence product is based on the Graphical Turbulence Guidance (GTG). The GTG and the associated Eddy Dissipation Rate (EDR) data scale used by GTG were both covered in detail in a previous ForeFlight article. It’s worth re-reading that post to brush up on the turbulence product, especially how the relationship between EDR and in-flight turbulence intensity changes based on aircraft weight. The information in that article applies equally to the US and global turbulence layers.

The US turbulence layer data are still based on GTG-3 with an available lead time of up to 18 hours. This layer displays the maximum EDR of clear air turbulence (CAT) and mountain wave turbulence (MWT). It is not intended to predict convection and thunderstorm turbulence sources, but may provide some guidance if the storm event is widespread. Furthermore, the graphics represent a snapshot at that time and not a forecast for a time range. Finally, it is important to realize that turbulence is a dynamic event and rapidly changing conditions may not be accurately reflected.

The global turbulence layer displays EDR derived from the GFS forecast model using a proprietary algorithm. This layer differs from the US GTG-3 derived layer in that the global turbulence data only forecasts CAT and not MWT. The forecast lead time can be up to 24 hours. The same reduced horizontal and vertical resolutions discussed previously in the global icing section apply to the global turbulence layer. Also, since the global turbulence layer uses GFS model data, the same reduced model run rate limitation applies (every 6 hours for GFS versus hourly for GTG-3), resulting in the US turbulence layer being updated more frequently. For all of these reasons, it’s important to use the US turbulence layer when operating within its coverage area.

Since the layer’s EDR scale is aircraft dependent, it is important to review the scale applicable to your aircraft category (the article linked above contains scales for light, medium, and heavy aircraft classes). The following color scheme is used in the turbulence map layer:

These new weather layers are an exciting and useful feature addition for our US and worldwide customers. Keep in mind that there is no human involvement in creating the turbulence and icing products and the information should be supplemented as much as possible with SIGMETs, AIRMETs, and PIREPs to understand the full weather picture.

Graphical Forecasts for Aviation (GFA) will become operational in April

Effective April 13, 2017, the experimental Graphical Forecasts for Aviation (GFA) produced by the NWS Aviation Weather Center (AWC) will transition to operational status. As you may have heard, the GFA was created in response to a formal request by the FAA to discontinue production of the textual Area Forecasts (FA). According to the NWS headquarters in Silver Spring, Maryland, “the requirements for the underlying meteorological information in the FA have not changed. The FAA recognizes that, given modern advances within the NWS, the legacy text FA is no longer the best source of en route flight planning weather information.”

The new graphical forecasts are designed to provide meteorological information equivalent to the textual FA. The GFA product includes observations and forecasts for the continental United States that provide data critical for aviation safety. The data is overlaid on high-resolution base maps that you can test drive here. Given this will be the replacement for the FA, it means that all of the forecasts will terminate at the U.S. borders. FAs for Hawaii, Alaska, the Caribbean, and the Gulf of Mexico will not be affected at this point in time.

For the time being, the legacy FA will continue to be generated in parallel with the GFA. The GFA is automated whereas the legacy FA is issued by forecasters at the AWC. At some point in the future, forecasters at the AWC will discontinue issuing this textual forecast. And don’t be surprised if the two forecasts contradict one another – let’s look at an example:

Below is the GFA valid at 23Z (issued at 2102Z) for cloud coverage along with tops and bases for the Northeast and Great Lakes. Notice that it forecasts just high cirrus clouds over a majority of Maine.

The GFA cloud forecast shows cloud coverage (color contours) as well as bases and tops. (click for larger image)

However, the legacy FA for this area shown below suggests a totally different forecast. This area forecast was amended by the FA forecaster for the eastern region at 1935Z. This forecast (highlighted below) suggests that after 21Z NW Maine is expected to have overcast clouds with bases at 2,000 – 3000 feet MSL. And NERN Maine is expected to have overcast cloud bases of 1,500 feet MSL. The forecaster also issued an AIRMET for IFR conditions covering most of the northeastern U.S.

000
FAUS41 KKCI 141935 AAA
FA1W  
BOSC FA 141935 AMD
SYNOPSIS AND VFR CLDS/WX
SYNOPSIS VALID UNTIL 151200
CLDS/WX VALID UNTIL 150600...OTLK VALID 150600-151200
ME NH VT MA RI CT NY LO NJ PA OH LE WV MD DC DE VA AND CSTL WTRS
.
SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN.
TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND IFR CONDS.
NON MSL HGTS DENOTED BY AGL OR CIG.
.
SYNOPSIS...SEE MIA FA FOR SYNOPSIS.
.
ME NH VT
NW ME/NRN-SW NH/VT...OVC020-030 TOP FL250. VIS 3SM -SN BR. 21Z
OVC020-030. VIS 3SM -SN BLSN. WND N 20G30KT. OTLK...IFR CIG SN
BLSN WND.
NERN ME...OVC030 TOP FL250. VIS 3-5SM -SN. 21Z OVC015. VIS 3SM
-SN BR. 03Z OVC015. VIS 3SM -SN BLSN. WND NELY G25KT. OTLK...IFR
CIG SN BLSN WND.

Notice the Synopsis section simply says “SEE MIA FA FOR SYNOPSIS.” Most pilots were probably not taught that the FA has a 3,000 character limit. So, with a raging Nor’easter occurring in the Northeast, they didn’t have enough characters available for the Boston FA to provide a complete synopsis. In that case, the forecaster opted to place the Boston synopsis in the Miami FA.

For the potential of clouds in Maine, the legacy FA proved to be much more accurate than the new GFA. Most of Maine was experiencing IFR conditions as denoted by AIRMET Sierra shown here.

At this point in time, the AWC is not providing public access to some of the underlying data you may see on the webpage mentioned above. We are busy at ForeFlight trying to determine how to best incorporate these forecasts from the GFA once they become available. So stay tuned.

True Colors of IR Satellite

Now in ForeFlight Mobile 8.3, you have a choice between one of two satellite layers on the ForeFlight Map view. The legacy satellite layer was renamed to Enhanced Satellite and the new layer is appropriately named Color IR Satellite. For many, the new satellite layer will look quite familiar. That’s because it was created to generally match the infrared (IR) satellite images located within the ForeFlight Imagery view. Or you may have seen similar color images on aviationweather.gov. While there are some differences, this color IR satellite layer has a rather high glance value to depict the locations of significant adverse weather and help to locate the height of the cloud tops.

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The older satellite layer was renamed to Enhanced Satellite with the new layer now called Color IR Satellite.

Why another satellite layer?

Back in November 2014, you may recall that we added color to the global satellite layer. Color was added to enhance or highlight the highest cloud tops that are typically associated with significant large synoptic-scale weather systems and deep, moist convection or thunderstorms. This is especially critical when flying in regions where ground-based radar data is sparse or nonexistent. The new satellite layer takes this a step further by colorizing the entire satellite layer based on a discrete cloud top temperature (in degrees Celsius).

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The Color IR Satellite layer should be viewed along with the sky coverage markers. You will notice that many pilot weather reports of icing tend to occur in regions of yellow, green and very light blue.

As I discussed in this earlier blog post high clouds are very cold and emit less infrared radiation than warmer clouds near Earth’s surface. Satellite sensors measure this radiation and meteorologists calibrate this to appropriate temperatures. Knowing the cloud top temperature can help us determine the relative height of the cloud tops and more importantly it can help us understand when supercooled liquid water may dominate the clouds creating a nasty icing threat.

Cloud tops and icing

In this new color satellite image, purple and darker shades of blue are indicative of tops at high altitudes. At the other end of the spectrum, shades of red and orange are indicative of shallow clouds with tops near the earth’s surface.

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Colors such as dark blue and purple on the left side of this scale (in degrees Celsius) represent the coldest (highest) cloud tops whereas colors on the right side of the scale represent the warmest (lowest) cloud tops.

To use the layer to determine the cloud top height over a particular region, zoom in on the area of concern in the Map view and note the temperature using the color scale above. Next, find the MSL altitude that corresponds to that temperature by referencing the local temperature aloft in that region. That gives you the cloud top height. For example, assume you were departing out of Garden City Regional Airport (KGCK) and wanted to know the height of the tops. Zooming in as shown below provides an orange color representing a temperature of approximately 0 degrees Celsius.

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The color IR satellite when zoomed in over Garden City shows mostly orange in this area. This corresponds to a temperature of roughly 0 degrees Celsius.

Using the winds/temperatures aloft provided in the Garden City popover, find the altitude that corresponds to that temperature. Perhaps a more accurate approach is to use a tool called a Skew-T log (p) diagram like the one pictured below. Starting from the surface, work your way up the red environmental temperature line and find the first altitude that corresponds to a temperature of 0 degrees Celsius. In this case, that corresponds to an altitude of 4,285 feet as shown on the left. Additionally, the diagram confirms that saturated conditions occur below this altitude representing the presence of clouds with unsaturated conditions above. This kind of analysis will provide the necessary confidence that a climb to 5,000 feet MSL will get you on top of this cloud deck.

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A Skew-T log (p) diagram like the one shown here for the Garden City Municipal Airport is an excellent tool to help locate the cloud top height. This depicts a forecast model representation of temperature (red line) and dewpoint temperature (blue line) as a function of height.

The more important colors are perhaps shades of yellow and green and maybe even very light blue. Using the color scale below, clouds with fairly warm subfreezing cloud top temperatures are likely to be dominated by supercooled liquid water and represent a airframe icing threat.

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The pale green, yellow and very light blue indicate regions where cloud top temperatures are in the  regime where the clouds below are dominated by supercooled liquid water representing an airframe icing hazard.

Don’t become complacent; clouds with colder (higher) tops can and do contain supercooled liquid water and may pack the threat of supercooled large drop (SLD) icing especially within deep, moist convection. However, these colder-topped clouds of darker shades of blue will normally be dominated by ice crystals or more likely be a mixed phase cloud (containing both ice crystals and supercooled liquid water). However, once ice nuclei begin to activate and ice crystals start to form in the cloud, the cloud tends to grow bigger ice crystals at the expense of supercooled liquid water which lessens the icing threat.

Masking out clear skies

As mentioned above, this layer is a close cousin of the static color IR satellite images found in the ForeFlight Imagery view. The static images show not only the temperature of the cloud tops using the same colors, but also the temperature of the surface of the earth. This can make it difficult to know where clouds exist and where the sky is clear. The main improvement is that the new satellite layer attempts to mask out regions where the sky is clear showing the map background in those regions instead of the surface temperature.

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Clear regions are masked out to show the underlying map below.

While this masking algorithm works a majority of the time, it can be difficult to get it right every single time simply using temperature alone. For example, anytime there’s a shallow low-topped stratus deck like the one shown below, the tops of the clouds may actually be slightly warmer than the surface of the earth courtesy of a surface-based temperature inversion. So the algorithm may have a difficult time discerning where it is cloudy or clear. So it’s important to always overlay the sky coverage markers to pick up on these issues when they occur.

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For some low-topped stratus events, it’s not unusual for the masking algorithm to show clear skies as it did here in the Midwest. The best way to detect this condition is to overlay the cloud coverage markers or during daylight hours check the Enhanced Satellite which operates in the visible spectrum during this time.

So during the late fall, winter and early spring, give this new satellite layer a quick glance. It’ll provide you with a method to determine the tops of most clouds and to reveal where there’s a definite risk of airframe ice.

‘Tis the season for airframe ice

Now that cold air has infiltrated a good portion of North America, it’s time to review one important aspect of airframe icing, namely, precipitation type. The three basic wintry precipitation types include snow, ice pellets (colloquially known as sleet) and freezing rain (also freezing drizzle). Surface observations (METARs) and forecasts such as TAFs typically report these precipitation types based on what’s reaching or expected to reach the surface. That’s a critical element to understand. If the surface temperature is expected to be even a degree or two above freezing, you may see a forecast for rain (RA) or drizzle (DZ) in the TAF instead of freezing rain (FZRA) or freezing drizzle (FZDZ). However, just 500 feet above the ground a serious icing hazard may be lurking. So let’s take a look at the three primary precipitation types and examine the temperature profile aloft that’s common for each.

Snow

Snowflakes are just collections of ice crystals that coalesce as they fall toward the Earth’s surface. For snow (SN) to reach the surface, there needs to be a deep moist layer that is, for the most part, entirely below freezing. More importantly, the key to getting snow is that the top of this moist layer must be sufficiently cold to produce those ice crystals. While there is no definitive temperature, ice crystals begin to dominate when the top of this moist layer is -12 degrees Celsius or colder. Precipitation continues to fall as snow when the temperature remains at or below 0 degrees Celsius from the cloud base to the ground. Wet snow is the result of temperatures slightly above freezing near the surface.

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A typical environmental temperature profile that produces snow. Image courtesy of NOAA National Severe Storms Laboratory.

Freezing rain

There are two processes in the atmosphere that can produce freezing rain (FZRA), namely, classical and nonclassical. The classic situation is what most pilots are taught during their primary training. That is, the precipitation starts out high in the cloud as snowflakes. These snowflakes fall through a melting layer that’s warmer than 0 degrees Celsius. If the melting layer is sufficiently warm and/or deep enough, it will melt those snowflakes turning them entirely into raindrops. That rain falls into a subfreezing layer and becomes freezing rain creating a significant airframe icing hazard.

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A typical temperature profile that produces classical freezing rain. Image courtesy of NOAA National Severe Storms Laboratory.

The nonclassical case is a bit more complex to explain, but essentially the entire process remains liquid. In other words, the precipitation high in the cloud doesn’t involve snow. This occurs when the weather system isn’t terribly deep and the top of the moist layer is at a temperature warmer than -12 degrees Celsius. Warmer subfreezing temperatures at the tops tend to prefer a liquid process over the production of ice crystals. In the non-classical case, the entire temperature profile aloft may be below freezing or may also have a melting layer. Regardless of the actual profile, the non-classical case is strictly an all-liquid process. In most situations, you’ll see a lot of tiny drops that produce a nasty freezing drizzle environment. Surprisingly, 92 percent of the cases are nonclassical based on a study done by the National Center for Atmospheric Research (NCAR).

Ice pellets

Ice pellets (PL) are similar to the classical freezing rain case mentioned above, except that the melting layer is very shallow. This doesn’t entirely melt the snowflake, and the drop retains a slushy inner core. These slushy drops refreeze as they fall through a deep layer of subfreezing air near the surface, and eventually reach the ground as hard little nuggets that bounce on impact.

sleet

A typical temperature profile that produces ice pellets. Image courtesy of NOAA National Severe Storms Laboratory.

Keep in mind that ice pellets often indicate the presence of supercooled large drop (SLD) icing aloft. While the frozen pellets will bounce right off of your aircraft while in flight (taking a bit of paint with it), they are often mixed with other forms of freezing precipitation including freezing rain especially at altitudes right below the shallow melting layer.

Here’s a little bit of ice pellet trivia. The abbreviation for ice pellets used to be PE. However, when rain and ice pellets occurred together with rain being the dominant precipitation type, the surface observation includes the term RAPE. This was deemed to be politically incorrect in English speaking countries and the abbreviation for ice pellets was then modified to PL.

So the next time you venture out this cold season, pay attention not only to the precipitation types that are being reported or forecast but also get a sense of the temperature profile aloft.

Aging Surface Observations

One of the more common concerns raised by ForeFlight customers is the age of surface observations or METARs shown within the app. They often wonder why the age of a METAR can be 60 or more minutes old in some cases. To understand why this occurs, let’s discuss how routine surface observations are taken throughout the world.

metar-age

The age shown here in the airport popover is based solely on the difference between the current time and the time the METAR was issued.

If you visit most any airport in the U.S., you’ll likely see one of two weather observing systems installed: the Automated Surface Observing System (ASOS) or the Automated Weather Observing System (AWOS). Both of these are capable of generating one or more weather reports each hour. Although these systems observe the weather nearly continuously in time, they will only generate official reports known as an aviation routine weather report or METAR when certain conditions apply.

Routine observations

For an ASOS, only one routine report is issued every hour, which is a key reason for the seemingly excessive age of these observations. If you pay close attention to the issuance time on METARs, you will notice that many routine observations are issued a few minutes before the top of each hour. Starting at 47:20 past the hour, the ASOS begins to make its routine observation. By 53:20, the hourly observation has been prepared and edited and should be ready for transmission. This routine report becomes the official hourly observation for the NWS. That’s the METAR you will see in the ForeFlight Mobile app.

It’s important to understand that the age presented in ForeFlight is based on the issuance time in the METAR regardless of when it was disseminated by the ASOS or AWOS station. Once each minute we pull down those latest observations directly from our interface with NOAA, parse them and add them directly into our database. After the METAR was issued, it is not unusual for several minutes to pass before it becomes available to ForeFlight. ForeFlight doesn’t typically receive and ingest the data until 4 or 5 minutes after this issuance time. Therefore, it’s very common that the routine observations will have an age of 4 or 5 minutes when updated. That means it’s quite normal to see an age of 64 or 65 minutes just before it gets refreshed by the latest hourly observation.

metar-refreshed

When a METAR is refreshed in ForeFlight Mobile an age of 4, 5 or 6 minutes is very common. For example, this METAR for Ellington, the METAR was updated 6 minutes ago.

An AWOS, on the other hand, typically issues three routine observations each hour or every 20 minutes. The typical interval is at 15, 35 and 55 minutes past each hour. However, you will find that these times will vary depending on the location. You may even run across some AWOS stations that operate similar to an ASOS, that is, one routine observation an hour.

SPECIs

If the weather is changing rapidly for the better or worse, special observations (SPECIs) are issued in addition to the routine hourly observations and include operationally significant changes to elements like wind direction, wind speed, ceiling height and visibility just to name a few. Given that the ASOS relentlessly measures the weather and could inundate pilots with more frequent special observations than a human observer, the system is purposely throttled to provide SPECIs only at 5-minute intervals. This is to limit the number of observations that can be transmitted during the hour when the weather is changing rapidly. Like the routine observations, SPECIs will also take several minutes to appear in ForeFlight after it is issued.

1-minute weather

Before you depart or when you approach an airport, it’s common to listen to the local weather broadcast over the dedicated ground-to-air frequency. This broadcast is referred to as the 1-minute weather. You can also get the latest weather by calling the stations dedicated telephone number. In either case, this automated weather is often more up to date than what you’d get over ATIS or via ForeFlight. At the moment, ForeFlight only provides the latest official observations that are disseminated in the form of a METAR or SPECI. In other words, we don’t currently provide the 1-minute weather you’d get over the phone or on the radio broadcast.

airport-wx-freq

You can find the frequency and phone number for the local ASOS or AWOS on the Airports view under Weather and Advisory tab.

Of course, all pilots want the latest and greatest information. However, that does not necessarily mean an hourly observation that’s 30 or more minutes old should be considered stale. In fact, if the weather hasn’t undergone an operationally significant change, the latest observation is likely still very representative of the weather at the airport.

Range of usefulness

You can’t talk about age unless you also wrap in a discussion about the range of usefulness of an observation. It’s not unusual for many pilots to assume that a particular observation is useful as far as 20 or more miles from the airport. That may be the case when the weather is fairly homogeneous across a large region. But in most situations, making that assumption can get you into trouble.

These official surface observations are taken to be representative of the weather within the terminal area. The terminal area is defined as the circular region within 5 statute miles from the center of the airport’s runway complex. In other words, they are point observations. Notice in the table below that many of the parameters reported in a METAR are valid only within 1 to 3 miles of the airport. So there are no guarantees that the weather is similar to what’s shown in the observation as you get outside of the terminal area.

table-validity-asos

This table defines the representative range from the airport of the various weather elements provided by the observing system.

So the next time you look at the age of latest surface observation don’t discount its operational value. When the weather isn’t changing all that rapidly, a single update each hour will be the normal case for many reporting stations throughout the world.

Why Use Convective Outlooks?

Perhaps one of the most underutilized weather products shown on the ForeFlight Map view are the yellow-shaded polygons called convective outlooks. On any given eight-hour shift, they are issued hourly by a highly trained meteorologist at the Aviation Weather Center (AWC) in Kansas City. In fact, convective SIGMETs shown by a red-shaded polygon are also issued by this same forecaster.

wst-outlooks

Convective outlooks, shown in yellow, can be displayed by picking the AIR/SIGMET/CWAs menu selection. Tapping on the TS button will display all convective SIGMETs as well as any convective outlooks.

Let’s start with convective SIGMETs

Convective SIGMETs (WSTs) define regions of airspace with active areas of thunderstorms that meet specific criteria. The important word here is active. In other words, convective SIGMETs represent more of a NOWcast for thunderstorms than a forecast. Here’s the way it works. Each and every hour the convective SIGMET forecaster at the AWC looks for thunderstorms throughout the lower 48 United States and coastal waters that meet specific criteria. A single cell pulse thunderstorm isn’t necessarily hazardous as long as you don’t fly through the same airspace that it occupies. However, when thunderstorms form long lines, are clustered close together in widespread areas, are embedded or severe, they become more of a threat to aviation and the forecaster will issue a convective SIGMET for those areas of thunderstorms at 55 minutes past each hour.

wst-siriusxm

A convective SIGMET outlined in red for a line of embedded thunderstorms as depicted from the SiriusXM satellite weather broadcast.

Despite the fact that convective SIGMETs are valid for two hours when issued, the following hour the forecaster will once again evaluate the convective threat and issue a new round of convective SIGMETs. Each new issuance at 55 minutes past the hour will supersede the previous set of convective SIGMETs. Effectively, no convective SIGMET will ever exist for two hours.

This is not to say that you must fly around convective SIGMET areas. For a convective SIGMET to be issued, the area of convection must contain significant radar echoes that fill a minimum of 40% of the area at least 3,000 square miles or 40% of a line of at least 60 miles in length. This leaves a fair amount of airspace to navigate through some convective SIGMET areas.

What about convective outlooks?

First, they are not “outlook SIGMETs” as I’ve seen them called. In fact, they are not SIGMETs at all. Unlike convective SIGMETs, convective outlooks are truly forecasts; there isn’t a requirement that active thunderstorms exist when they are issued. Instead, they define larger regions of airspace that are expected to contain thunderstorms that meet convective SIGMET criteria in the next two to six hours after the outlook was issued. These may include ongoing areas or lines of convection covered by a convective SIGMET or they may include new areas or lines of thunderstorms that are expected to develop and reach convective SIGMET criteria in the two to six hours valid period.

wst-outlook

A convective outlook is outlined in yellow. This shows the region where convective SIGMETs are likely to be issued within the next two to six hours. The text of the outlook provides the effective time.

That two to six hour window is a perfect “sweet spot” for many of us making flights. There may not be any thunderstorms when you go to depart, but if your proposed route takes you through one of these convective outlook areas in the valid time specified you may see one or more convective SIGMETs issued within this outlook area during your flight.

outlook-with-cwa

When convection doesn’t quite meet convective SIGMET criteria you may still see a Center Weather Advisory (CWA) issued for thunderstorms as shown in this image. CWAs are issued by meteorologists at the Center Weather Service Units and coordinated with forecasters at the Aviation Weather Center.

What about ADS-B or SiriusXM?

At the moment, convective outlooks are not broadcast over the ADS-B ground stations and are not part of the SiriusXM satellite weather broadcast. In ForeFlight, we attempt to preserve the latest convective outlooks until they expire six hours later. So be sure to use the Pack feature of ForeFlight prior to departure.

Tips On Using SiriusXM Satellite Weather In ForeFlight

With the release of ForeFlight Mobile 8.1 you now have the opportunity to use the best portable en route weather system available courtesy of our partnership with SiriusXM Satellite Radio. The SiriusXM Pilot for ForeFlight subscription tier has been uniquely designed to provide all of the essential weather data during every phase of flight. In fact, within about 15 minutes of turning on the SXAR1 and connecting to the ForeFlight Mobile app, you’ll have seamless access to a comprehensive set of weather products well before you close the door on the cockpit and depart. Here are some of my tips to safely use this unique collection of weather data.

Hurricane Hermine

SiriusXM radar depiction of Hurricane Hermine as it approached the Florida coast in early September.

The SiriusXM source label

Knowing the source of the data you are using is paramount since weather data ages quickly. When connected to the SXAR1, you’ll see a SiriusXM label under the tappable timestamp button in the upper left of the Map view. Moreover, every weather product provided through the SiriusXM broadcast includes a source label in parentheses along with its relative age like the one depicted in the image below. This is similar to the ADS-B label shown when connected to Stratus. While connected to the SXAR1 in flight, always be sure to check for the presence of the SiriusXM label. Seeing this label will confirm that you are using the most current weather available.

siriusxm-tag-taf

Products received from the SiriusXM broadcast and displayed in ForeFlight will be labeled with a SiriusXM tag along side the product’s age as shown here for a terminal aerodrome forecast (TAF) for the Cape Girardeau Regional Airport.

Lightning

During the warm season, lightning from ground-based sensors is perhaps one of the most critical weather elements to have available in the cockpit. Any area of weather that includes lightning means there’s a darn good chance you will encounter severe or extreme convective turbulence in and around that weather. While most of the serious thunderstorms will be included within the boundary of a convective SIGMET, not all thunderstorms will meet convective SIGMET criteria. Moreover, thunderstorms often occur outside of these areas, especially during a rapidly developing convective event.

Lightning is broadcast over SiriusXM every five minutes and provides pilots with a birds-eye view of where the truly nasty convective weather is located. Moreover, both cloud-to-ground (CG) and intracloud (IC) lightning are part of this broadcast. It’s quite important that both types are included since many severe storms are often dominated by IC lightning.

With SiriusXM not every lightning strike is broadcast. Instead, a single lightning symbol is shown anytime one or more strikes have occurred within a generous 0.5 nautical mile grid. So when you pinch-and-zoom way in on the ForeFlight map as shown below, you’ll notice the lightning bolt symbols are aligned in this 0.5 nautical mile gridded pattern. ForeFlight retains the most recent 10 minutes of lightning data which tends to align with the most recent radar depiction very well.

SiriusXM Lightning grid

A zoomed-in view of SiriusXM lightning reveals it’s gridded nature.

Lightning is detected even in regions where radar coverage is not present. This can be extremely useful when flying outside of the NEXRAD radar coverage area. You’ll see lightning depicted in regions over the Gulf of Mexico and Caribbean as well as the coastal waters of the U.S. in the western Atlantic and eastern Pacific Oceans. It will also include lightning in Canada, Mexico, Central America and the northern-most regions of South America. Although there is SiriusXM NEXRAD coverage provided around Puerto Rico and the U.S. Virgin Islands (using the base reflectivity from the lowest tilt), having lightning shown in other locations in the Caribbean will help pilots avoid the nasty tropical convection that occurs in these highly traveled areas where there isn’t NEXRAD coverage.

lightning-south-america

SiriusXM radar coverage is available using the base reflectivity layer from the lowest tilt around Puerto Rico and U.S. Virgin Islands. You will also see lightning depicted outside of the standard NEXRAD coverage area as far south as the northern portions of South America.

Storm attribute markers

Pilots have become accustomed to seeing echo top heights and storm track identification markers in ForeFlight. With SiriusXM you’ll get those same NEXRAD storm attributes. This includes a generic storm marker with an echo top height shown in 100s of feet in addition to cells that have signatures of hail, mesocyclone and tornadoes using the symbols shown below. Echo top heights are only shown for tops 20,000 feet and higher.

markers

Storm attribute markers include hail, mesocyclone and tornadic vortex signature. Under the settings, these SiriusXM Storm Markers can be switched on and off as desired.

In most cases these storm attribute markers will also contain a direction and speed of the cell being tracked. Similar to the other storm tracks you will see depicted on the radar mosaic in ForeFlight, SiriusXM tracks will contain an arrow showing the direction of movement as well as the speed. If the cell is moving at a speed of more than 10 knots, you’ll also see two black dots depicted on the arrow that loosely estimates the position of that storm cell in 20 and 40 minutes based on the cell’s current speed and direction provided. The arrowhead represents the estimated location of the cell in 60 minutes.

Confusing Storm Attribute Markers

During a rapidly developing convective event or when thunderstorms are dissipating, it’s quite common to see the storm tracks for adjacent cells point in opposite direction.

While these markers provide additional information about a storm cell, keep in mind that there will be times when the storm tracks for adjacent cells may provide conflicting information as you can see in the example shown above. It’s unlikely these cells are actually moving toward each other. This typically occurs during the initial stage of thunderstorm evolution especially when there’s an area of rapidly developing convection. Animating the radar is perhaps the best way to note the direction of movement of an area of weather.

tvs-hermine

Shown here are several storm attribute markers to include mesocyclone circulation and tornadic vortex signatures from Tropical Storm Hermine as it passed off the coast of South Carolina.

Radar layers

The SiriusXM composite reflectivity and base reflectivity from the lowest tilt have the same 2 km horizontal resolution as you may have experienced with the regional radar broadcast provided by ADS-B. On the left is the regional composite reflectivity mosaic broadcast by ADS-B using the Stratus 2 receiver. On the other hand, the right side is the SiriusXM mosaic just a minute earlier. While the mapping of dBZ levels to color may be a little different for the two composite reflectivity sources, the overall spatial resolution is the same.

ads-b-vs-siriusxm

Regional composite reflectivity from ADS-B shown on the left and composite reflectivity from SiriusXM shown on the right. Both have a similar resolution.

There’s no doubt that the overall qualitative glance value is practically the same between the two radar depictions above. You’ll find, however, that the latest SiriusXM broadcast will be about 5 minutes fresher on average than what you get through ADS-B.

Partial radar refresh

You may occasionally notice that both of the radar mosaics may take a short period of time to completely refresh the Map view for the entire radar coverage area when a new NEXRAD broadcast is being processed. During the refresh, it will be common to see “Radar not available” briefly depicted over regions where coverage is normally provided as shown below for the base reflectivity mosaic from the lowest tilt.

Partial refresh

Partial updates to both the composite reflectivity and base reflectivity from the lowest tilt should be expected when the newest radar broadcast is being processed.

This is because radar data received by the SXAR1 rarely comes as a continuous frame of data. Often this data is broadcast in blocks over a short period of time. This is especially true for the base reflectivity mosaic from the lowest tilt. To avoid holding back the entire radar mosaic until every single byte is received, we decided to provide the newest radar in pieces as it arrives. Whether or not this occurs and how long it takes to provide a complete picture, depends on the amount of radar echoes throughout the entire coverage area. During times of high convective activity or large-scale precipitation, expect the refresh to be a bit slower, typically 20 to 30 seconds.

If you believe in Murphy’s Law, this refresh delay will rear its ugly head at the most inopportune time. If the refresh takes uncomfortably too long while in flight, you can always switch to the other radar depiction in the short term.

Also includes Canada

Unlike ADS-B, the SiriusXM radar depiction from the lowest tilt does include Canadian Doppler radar information as well (Canadian radar is not included in the composite reflectivity mosaic). You won’t see any storm tracks or echo tops depicted by Canadian radar data, but this does extend the radar coverage to the southern most part of Canada for those pilots that fly to this area frequently. In addition to radar, you will see winds and temperatures aloft depicted in Canada as well as METARs, TAFs and PIREPs.

Winds and temperatures aloft

The winds aloft layer is populated by model-based winds (not observations) from the SiriusXM broadcast. These are an accurate representation of the current winds at 3,000 ft MSL up to FL480 at 3,000 ft intervals. This is a similar presentation to what you will find with the winds aloft layer when connected to the Internet. Tapping on any wind barb will provide the wind direction, wind speed and temperature at the altitude selected.

winds-aloft

While in flight, you will see updates to the current winds once each hour. At this time there are no forecasts of winds aloft provided through SiriusXM valid beyond the current time. Consequently, the SiriusXM winds are not used in performance calculations, so you should anticipate using the pack feature to have an estimation of winds aloft along your route while in flight.