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.


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.


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.


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.

Apple iOS 9.3.4 and ForeFlight

UPDATE August 12, 2016: After testing iOS 9.3.4 this week, we’re ready to issue an “all-clear” to ForeFlight customers. Feel free to update at your own convenience.

ORIGINAL POST August 5, 2016: We are performing compatibility testing between ForeFlight and the newly released iOS 9.3.4 to ensure that everything is working smoothly. We will update this post with an “all-clear” when testing is completed.

L-3 Lynx Connectivity Available in ForeFlight Mobile

ForeFlight’s Connect platform continues to expand to include L-3’s Lynx line of ADS-B products. ForeFlight customers can connect wirelessly via Wi-Fi to L-3’s Lynx NGT-9000, -2000, and -2500 models to receive ADS-B traffic and weather and GPS data in ForeFlight. The NGT-9000, -9000+, -9000D, and 9000D+ all-in-one transponder solutions replace your current transponder to provide FAA mandate-compliant Mode S Extended Squitter capability with an embedded WAAS GPS. Lynx NGT-2000 and -2500 models also work seamlessly with the ForeFlight app and provide a low-cost 978 MHz ADS-B solution that integrates with legacy transponders. Click here for L-3 Lynx pricing and availability. All ForeFlight subscription plans include avionics connectivity.

Connect to L-3 Lynx to receive ADS-B traffic and weather and GPS position in ForeFlight

Once you connect your iPad or iPhone to the Lynx’s WiFi network, you can see details of the connection in ForeFlight Mobile in More > Devices (tap the L-3 Lynx box for additional information) and you can overlay ADS-B weather and traffic information on the Maps view using the drop-down in the upper-left corner of the screen.

L-3 Lynx support is available with ForeFlight Mobile 7.7.2. You can check your app version at the top of More > About; if you don’t yet have version 7.7.2, you can upgrade directly by opening this link on your iPad or iPhone.

Bulletin: July 22 Data Updates

New downloads are available for the July 21, 2016 – August 18, 2016 period. An updated New York Sectional has been released with the correct depiction of Prohibited Area P-67. This addresses an FAA Safety Alert.

A new Airport and Nav Database (July 22 Update) is also available. This improves Procedure Advisor data at several airports.

All customers will be prompted to download these updates inside of ForeFlight Mobile.

July 21 Data Updates

New downloads are available for the July 21, 2016 – August 18, 2016 period. New Taxi Diagrams and A/FD and Terminal Procedures are available for the state of Arizona. This update adds a missing taxiway on the Airport Diagram at KFFZ (Falcon Field) and addresses an FAA Safety Alert.

New Visual Navigation Charts are also available for our Canada region customers. The Vancouver VTA and Anticosti, Gander, Moncton, and Vancouver VNC charts have been updated.

All customers will be prompted to download these updates inside of ForeFlight Mobile.

Apple iOS 9.3.3 and ForeFlight

UPDATE: July 21, 2016: After carefully testing iOS 9.3.3 this week, we’re ready to issue an “all clear” to ForeFlight customers. Feel free to update at your own convenience.

ORIGINAL POST July 18, 2016: We are performing compatibility testing between ForeFlight and the newly released iOS 9.3.3 to ensure that everything is working smoothly. We will update this post with an “all-clear” when testing is completed.

Bulletin: July 21 Data Updates

Data updates are now available to download for the July 21, 2016 – August 18, 2016 and July 21, 2016 – September 15, 2016 periods:

  • Airport and Navigation Database
  • Documents
    • EAA AirVenture Oshkosh 2016 NOTAM
    • Pilot’s Guide to ForeFlight Mobile
    • ForeFlight Mobile Legends
    • Logbook in ForeFlight Mobile
  • ForeFlight Airport Diagrams, including updates to the following airports:
0V4 18A 1M4 49B 4M9 5A6
5R8 6L4 7W4 A39 BGBW BIKF
E63 EKCH F41 I16 I75 KAAO
X07 X60 Y51

From the FAA:

  • VFR Charts and Terminal Area Charts
  • High and Low Enroutes, Area Charts
  • Caribbean High and Low Enroutes, Area Charts
  • Ocean Planning Charts
  • Taxi Diagrams
  • Terminal Procedures
  • Airport/Facility Diagrams
  • Documents

For Canada region customers:

  • Taxi Diagrams
  • Terminal Procedures
  • High and Low Enroutes
  • Canada Flight Supplement
  • Documents

For our Military Flight Bag customers:

  • Georeferenced worldwide D-FLIP Terminal Procedures
  • Georeferenced worldwide D-FLIP Airport Diagrams
  • CSA High and Low Enroutes, Area Charts
  • PAA High and Low Enroutes, Area Charts
  • D-FLIP Publications such as Planning Change Notices, Area Planning Documents,
  • Chart Supplements, Enroute Change Notices, and Terminal Change Notices.
  • Airfield Qualification Program (AQP) diagrams
  • Airfield Suitability and Restrictions Report (Giant Report)
  • Airport/Facility Directory

All customers will be prompted to download these updates inside of ForeFlight Mobile.

Logbook Flight Sharing, Stratus ESG Support, New Radar Layer in ForeFlight 7.7

ForeFlight 7.7 introduces the ability to share Logbook draft entries with other pilots, as well as a new radar layer, a new rate of descent instrument, Stratus ESG support, and lots of work under the hood to improve general map performance.

Flight Logging Just Got Easier with Flight Sharing

The new Flight Sharing feature in ForeFlight Logbook makes it easy for pilots to send and receive draft flight entries. Pilots can share a flight with one or more people right from the ForeFlight app. The receiving party then modifies and accepts the entry into their own Logbook. Flight Sharing makes it convenient when practicing approaches with a friend– use one iPad to collect the flight details, then simply share the entry. It is also a time-saver for corporate flight crews who can now share a logbook entry between the Captain and First Officer, reducing time spent on the administrative aspect of a flight.

You can review and make edits to the shared entry before adding it to your Logbook

Shared entries are just like drafts from Track Logs – review and edit the information, then tap Approve to add it to your Logbook.

Track Medical Currency in LogbookTrack the time left on your medical certificate with other currency types

Don’t let your medical expiration sneak up on you. When you add your medical certificate to the Logbook Qualifications section, you can now also add it to your currency summary view. This keeps the time remaining until your medical certificate expires front and center.


Stratus ESG Support and Firmware Upgrade for Stratus 1S/2S

Bundled with ForeFlight 7.7 is a firmware upgrade for Stratus 1S and 2S receivers. This upgrade adds support for the Stratus ESG, Appareo’s new all-in-one ADS-B Out solution. Stratus 1S and 2S devices can connect to the Stratus ESG via a USB cable to take advantage of its auxiliary power for continual charging, as well as the transponder’s externally mounted WAAS GPS and ADS-B receivers for maximum reception.

Stratus ESG with 2S and iPad

The upgrade also adds new features to the Stratus 2S. The built-in Flight Data Recorder now has automatic flight leg detection which automatically stops a Stratus Track Log and starts a new one when a full landing is detected. In addition, customers now have the option to save AHRS calibration settings between uses – this is especially helpful for taildragger aircraft pilots who set ‘straight and level’ attitude while inflight.

New ‘Lowest Tilt’ Radar Layer

For more informed preflight planning, you can now choose between the existing NEXRAD composite reflectivity layer and a new NEXRAD base reflectivity from the lowest elevation angle, or Lowest Tilt, layer. The current radar layer — renamed ‘Radar (Composite)’ — does what its name implies: it shows a composite view of multiple angles of radar scans. The new Radar (Lowest Tilt) layer shows only the lowest angle scan, generally providing a more accurate picture of where precipitation is actually reaching the ground.

Lowest-tilt radar provides a better indication of where precipitation is reaching the ground

The composite radar image at left shows precipitation over Atlanta, but the lowest-tilt scan on the right reveals that precipitation is only reaching the ground well west of the city.

In addition, you can display either radar layer in the low resolution, 4-color scheme defined by the Radio Technical Commission for Aeronautics as the standard for airborne radar coloring. This option is available in the Map Settings menu as “Four-color Radar”.

Display radar in a basic four-color formatCheck out Scott Dennstaedt’s blog post to learn more about these new radar features.

Finally, the Lightning layer no longer declutters groups of lightning strikes, allowing you to see all the strikes in a given area to get a better sense of where dangerous convection is occurring in a storm.

Find Your Rate of Descent to Destination

Also on the Maps view is a new option in the instrument panel: Descent to Dest. This instrument uses your GPS ground speed, GPS altitude, and distance to destination to compute the required rate of descent in feet per minute to be at your destination elevation upon arrival.

Descent to Dest Instrument

The Descent to Dest instrument shows the rate of descent required to be at destination elevation upon arrival.

Military Flight Bag Gets new Data Features

Military Flight Bag (or MFB), our dedicated subscription plan for military customers, now allows charts and data to be loaded onto an iPad over a wired computer connection — a process termed “sideloading”. While most of us have ready access to high-speed Wi-Fi and cellular connections, many of our military customers operate in areas of the world with slow or no internet – imagine trying to download a 2GB chart update over dial-up. Sideloading allows these updates to be delivered to multiple devices by connecting them to a central computer with the data already on it, giving military customers added flexibility in how they operate around the world.

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.


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.


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.


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).


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


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.


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 Terrain Map Available for Download Ahead of ForeFlight 7.7

In preparation for ForeFlight 7.7, coming this week, we have released a new Terrain Map for download in the app. ForeFlight 7.7 includes a number of under-the-hood improvements to the ForeFlight Map Engine, which requires the new Terrain Map.

The new download replaces the old Terrain Map for ForeFlight 7.7.

The new Terrain Map is available now in More > Downloads, at the bottom of the Required Downloads section. Please make sure to download it before your first flight with ForeFlight 7.7, as it will be required in order to use the Terrain Map layer on the Maps view.

Also, don’t forget that ForeFlight 7.7 changes the minimum required iOS version from iOS 8.2 to iOS 9.2, so if you haven’t already updated your devices to at least iOS 9.2 please do so before downloading ForeFlight 7.7.