Many aircraft manufacturers now include satellite weather services with new electronic flight display (EFD) systems. EFDs give a pilot access to many of the satellite weather services available. Products available to a pilot on a typical display [Figure 12-21] are listed as follows (the letters in parentheses indicate the soft key to press in order to access the data):

• Graphical NEXRAD data (NEXRAD)
• Graphical METAR data (METAR)
• Textual METAR data
• Textual terminal aerodrome forecasts (TAF)
• City forecast data
• Graphical wind data (WIND)
• Graphical echo tops (ECHO TOPS)
• Graphical cloud tops (CLD TOPS)
• Graphical lightning strikes (LTNG)
• Graphical storm cell movement (CELL MOV)
• NEXRAD radar coverage
• SIGMETs/AIRMETs (SIG/AIR)
• Surface analysis to include city forecasts (SFC)
• County warnings (COUNTY)
• Freezing levels (FRZ LVL)
• Hurricane track (CYCLONE)
• Temporary flight restrictions (TFR)

Pilots must be familiar with any EFD or MFD used and the satellite weather products available on the display.

12.8.1 Weather Products Age and Expiration #

The information displayed using a satellite weather link is near real time but should not be thought of as instantaneous up-to-date information. Each type of weather display is stamped with the age information on the MFD. The time is referenced from Zulu when the information was assembled at the ground station. The age should not be assumed to be the time when the FIS received the information from the satellite.

Two types of weather are displayed on the screen: “current” weather and forecast data. Current information is displayed by an age while the forecast data has a data stamp. [Figure 12-22]

12.8.2 The Next Generation Weather Radar System (NEXRAD) #

The NEXRAD system is comprised of a series of 159 Weather Surveillance Radar–1988 Doppler (WSR-88D) sites situated throughout the United States as well as selected overseas sites. The NEXRAD system is a joint venture between the United States Department of Commerce (DOC), the United States Department of Defense (DOD), as well as the United States Department of Transportation (DOT). The individual agencies that have control over the system are the NWS, Air Force Weather Agency (AFWA), and the FAA. [Figure 12-23]

NEXRAD radar produces two levels of products: level II and level III.

12.8.3 Level II Data Products #

All NEXRAD level-II data products are available through the National Climatic Data Center (NCDC). Level II data consists of the three meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width.

12.8.4 Level III Data Products #

There are 41 products routinely available through the NCDC. Level III graphic products are available as digital images, color hard copy, gray scale hard copy, or acetate overlay copies. This information is then encoded and disseminated through the satellite weather system as well as other sources.

NEXRAD level III data for up to a 2,000 mile range can be displayed. It is important to realize that the radar image is not real time and can be up to 5 minutes old. At no time should the images be used as storm penetrating radar nor to navigate through a line of storms. The images display should only be used as a reference.

NEXRAD radar is mutually exclusive of Topographic (TOPO), TERRAIN, and STORMSCOPE. When NEXRAD is turned on, TOPO, TERRAIN, and STORMSCOPE are turned off because the colors used to display intensities are very similar.

In addition to utilizing the soft keys to activate the NEXRAD display, the pilot also has the option of setting the desired range. It is possible to zoom in on a specific area of the display in order to gain a more detailed picture of the radar display. [Figure 12-24]

12.8.5 NEXRAD Abnormalities #

Although NEXRAD is a compilation of stations across the country, there can be abnormalities associated with the system. Some of the abnormalities are listed below:

• Ground clutter
• Strobes and spurious radar data
• Sun strobes, when the radar antenna points directly at the sun
• Interference from buildings or mountains, which may cause shadows
• Military aircraft which deploy metallic dust and may reflect the radar signature

12.8.6 NEXRAD Limitations #

In addition to the abnormalities listed, the NEXRAD system does have some specific limitations. Base Reflectivity: the NEXRAD base reflectivity does not provide adequate information from which to determine cloud layers or type of precipitation with respect to hail versus rain. Therefore, a pilot may mistake rain for hail.

In addition, the base reflectivity is sampled at the minimum antenna elevation angle; with this minimum angle, an individual site cannot depict high altitude storms directly over the station, leaving an area of null coverage if an adjacent site does not also cover the affected area.

Resolution Display: the resolution of the displayed data poses additional concerns when the range is decreased. The minimum resolution for NEXRAD returns is two kilometers. This means that when the display range is zoomed in to approximately ten miles, the individual square return boxes will be more prevalent. Each square will indicate the strongest display return within that two kilometer square area.

12.8.7 AIRMET/SIGMET Display #

AIRMET/SIGMET information is available for the displayed viewing range on the MFD. Some displays are capable of displaying weather information for a 2,000 mile range. AIRMETS/SIGMETS are displayed by dashed lines on the map. [Figure 12-25]

The legend box denotes the various colors used to depict the AIRMETs such as icing, turbulence, IFR weather, mountain obscuration as well as surface winds. [Figure 12-26] The great advantage of the graphically displayed AIRMET/SIGMET boundary box is the pilot can see the extent of the area that the report covers without manually plotting the points.

12.8.8 Graphical METARs #

METARs can be displayed on the multi-function display. Each reporting station that has a METAR/TAF available is depicted by a flag from the center of the airport symbol. Each flag is color coded to depict the type of weather that is currently reported at that station. A legend is available to assist users in determining what each flag color represents. [Figure 12-27]

The graphical METAR display shows all available reporting stations within the set viewing range. By setting the range knob up to a 2,000 mile range, pilots can pan around the display map to check the current conditions of various airports along the route of flight.

By understanding what each colored flag indicates, a pilot can quickly determine where weather patterns display marginal weather, IFR, or areas of VFR. These flags make it easy to determine weather at a specific airport should the need arise to divert from the intended airport of landing.