Figure 13-13. Significant weather prognostic chart.
Effective September 1, 2015, the four-panel Low Level
SFC-240 chart was replaced with a two-panel chart. The new
two-panel chart will be the same as the top two panels in the
former four-panel chart, depicting the freezing level and areas
of IFR, MVFR, and moderate or greater turbulence. The bottom
two panels of the chart have been removed. In lieu of these
bottom two panels, an enhanced surface chart that includes
fronts, pressure, precipitation type, precipitation intensity, and
weather type, is displayed. The green precipitation polygons
will be replaced by shaded precipitation areas using the
National Digital Forecast Database (NDFD) weather grid.
Figure 13-13 depicts the new two-panel significant weather
prognostic chart, as well as the symbols typically used to
depict precipitation. The two panels depict freezing levels,
turbulence, and low cloud ceilings and/or restrictions to
visibility (shown as contoured areas of MVFR and IFR
conditions). These charts enable the pilot to pictorially
evaluate existing and potential weather hazards they may
encounter. Pilots can balance weather phenomena with
their aircraft capability and skill set resulting in aeronautical
decision-making appropriate to the flight. Prognostic charts
are an excellent source of information for preflight planning;
however, this chart should be viewed in light of current
conditions and specific local area forecasts.
The 36- and 48-hour significant weather prognostic chart is
an extension of the 12- and 24-hour forecast. This chart is
issued twice a day. It typically contains forecast positions and
characteristics of pressure patterns, fronts, and precipitation.
An example of a 36- and 48-hour surface prognostic chart is
shown in Figure 13-14.
ATC Radar Weather Displays
Although ATC systems cannot always detect the presence
or absence of clouds, they can often determine the intensity
of a precipitation area, but the specific character of that area
(snow, rain, hail, VIRGA, etc.) cannot be determined. For
this reason, ATC refers to all weather areas displayed on ATC
radar scopes as “precipitation.”
ARTCC facilities normally use a Weather and Radar
Processor (WARP) to display a mosaic of data obtained
from multiple NEXRAD sites. There is a time delay between
actual conditions and those displayed to the controller.
The precipitation data on the ARTCC controller’s display
could be up to 6 minutes old. The WARP processor is only
used in ARTCC facilities. All ATC facilities using radar
weather processors with the ability to determine precipitation
intensity, describe the intensity to pilots as:
• Light
• Moderate
• Heavy
• Extreme
When the WARP is not available, a second system, the
narrowband Air Route Surveillance Radar (ARSR) can
display two distinct levels of precipitation intensity that
is described to pilots as “MODERATE and “HEAVY TO
EXTREME.”
ATC facilities that cannot display the intensity levels of
precipitation due to equipment limitations describe the
location of the precipitation area by geographic position or
position relative to the aircraft. Since the intensity level is not
available, the controller states “INTENSITY UNKNOWN.”
ATC radar is not able to detect turbulence. Generally,
turbulence can be expected to occur as the rate of rainfall or
intensity of precipitation increases. Turbulence associated
with greater rates of precipitation is normally more severe than
Figure 13-14. 36- (top) and 48-hour (bottom) surface prognostic chart.
any associated with lesser rates of precipitation. Turbulence
should be expected to occur near convective activity, even
in clear air. Thunderstorms are a form of convective activity
that imply severe or greater turbulence. Operation within
20 miles of thunderstorms should be approached with great
caution, as the severity of turbulence can be much greater than
the precipitation intensity might indicate.
Weather Avoidance Assistance
To the extent possible, controllers will issue pertinent
information on weather and assist pilots in avoiding such
areas when requested. Pilots should respond to a weather
advisory by either acknowledging the advisory or by
acknowledging the advisory and requesting an alternative
course of action as follows:
• Request to deviate off course by stating the number
of miles and the direction of the requested deviation.
• Request a new route to avoid the affected area.
• Request a change of altitude.
• Request radar vectors around the affected areas.
The controller’s primary function is to provide safe separation
between aircraft. Any additional service, such as weather
avoidance assistance, can only be provided to the extent
that it does not detract from the primary function. It’s also
worth noting that the separation workload is generally greater
than normal when weather disrupts the usual flow of traffic.
ATC radar limitations and frequency congestion may also
be a factor in limiting the controller’s capability to provide
additional service.
Electronic Flight Displays (EFD) /Multi-
Function Display (MFD) Weather
Many aircraft manufacturers now include data link weather
services with new electronic flight display (EFD) systems.
EFDs give a pilot access to many of the data link weather
services available.
Products available to a pilot on the display pictured in
Figure 13-15 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 T,,,OPS)
• Graphical cloud tops (CLD TOPS)
• Graphical lightning strikes (LTNG)
• Graphical storm cell movement (CELL MOV)
• NEXRAD radar coverage (information displayed with
the NEXRAD data)
• 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
data link weather products available on the display.
Weather Products Age and Expiration
The information displayed using a data link 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 data link.
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 in the form
of “__ / __ __ : __.” [Figure 13-16]
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 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 13-17]
NEXRAD 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. The NTSB has reported on 2
fatal accidents where in-cockpit NEXRAD mosaic imagery
was available to pilots operating near quickly-developing and
fast-moving convective weather. In one of these accidents,
the images were from 6 to 8 minutes old. In some cases,
NEXRAD data can age significantly by the time the mosaic
image is created. In some extreme latency cases, the actual
Figure 13-15. Information page.
Figure 13-16. List of weather products and the expiration times of each.
NEXRAD
RAIN
MIX
SNOW
H
E
A
V
Y
L
I
G
H
T
SIGMET
AIRMET
__/__ __:__
__/__ __:__
NORTH UP
does not show the age of the actual weather conditions,
but rather the age of the mosaic image. The actual weather
conditions could be up to 15 to 20 minutes OLDER than
the age indicated on the display. You should consider this
age of the oldest NEXRAD data in the mosaic can exceed
the age indication in the cockpit by 15 to 20 minutes. Even
small-time differences between the age indicator and actual
conditions can be important for safety of flight, especially
when considering fast-moving weather hazards, quickly
developing weather scenarios, and/or fast-moving aircraft.
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.
Lightning information is available to assist when NEXRAD
is enabled. This presents a more comprehensive picture of
the weather in the surrounding area.
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 13-18]
What Can Pilots Do?
Remember that the in-cockpit NEXRAD display depicts
where the weather WAS, not where it IS. The age indicator
Figure 13-17. NEXRAD radar display.
Figure 13-18. NEXRAD radar display (500 mile range). The individual color gradients can be easily discerned and interpreted via the
legend in the upper right corner of the screen. Additional information can be gained by pressing the LEGEND soft key, which displays
the legend page.