Chapter 27, Forecasts 27-1
27 Forecasts
27.1 Introduction
The fourth of five types of aviation weather information discussed in this handbook is forecasts.
This chapter will discuss many forecast products produced primarily by the NWS that are either specific to
aviation or are public products of interest to aviation users.
As with other products discussed in this handbook, the visualization of these products has evolved over the
past decade with the use of internet websites. The use of static black and white depictions of aviation
forecasts is almost a thing of the past. Today ’s websites provide the forecast products in color and offer
options to select and overlay multiple products.
Today’s aviation weather website s, including those of the NWS, continue to improve the content and
visualization of forecast products. Unfortunately, it is not practical to update this handbook with every
change to a weather product.
Examples of weather products in this handbook represent one way of how they can be visualized on a user’s
viewing device ( e.g., computer, tablet, mobile phone, or cockpit display ). The examples shown in this
handbook are from the NWS’ websites.
Chapter 27, Forecasts 27-2
For this handbook, forecasts include the following:
• Winds and Temperatures Aloft Forecasts
• Terminal Aerodrome Forecasts (TAF)
• Aviation Surface Forecasts
• Aviation Clouds Forecasts
• Graphical Aviation Forecast (GFA)
• Area Forecasts (FA), Alaska FA
• Alaska Graphical Forecasts:
o Flying Weather
o Surface Forecast
o Icing Forecast
o Turbulence Forecast
o Convective Outlook
• World Area Forecast System (WAFS) Forecasts
• Significant Weather (SIGWX) Forecasts:
o Low-Level
o Mid-Level
o High-Level
• Surface Prognostic Forecasts
• Upper Air Forecasts
• Freezing Level Forecasts
• Forecast Icing Product (FIP)
• Graphical Turbulence Guidance (GTG) Forecasts
• Cloud Tops Forecasts
• Localized Aviation Model Output Statistics (MOS) Program (LAMP) Forecasts
o Alaska Aviation Guidance (AAG) Weather Product
Chapter 27, Forecasts 27-3
• Additional Convection Products:
o Convective Outlook
o Traffic Flow Management (TFM) Convective Forecast (TCF)
o Extended Convective Forecast Product (ECFP)
o Watch Notification Messages
o Corridor Integrated Weather System and Consolidated Storm Prediction for Aviation
• Route Forecasts (ROFOR)
• Aviation Forecast Discussions (AFD)
• Meteorological Impact Statements (MIS)
• Soaring Forecasts
• Balloon Forecasts
27.2 Winds and Temperatures Aloft
There are many wind and temperature aloft forecasts and products produced by the NWS. Each NWP model
(i.e., sometimes referred to as computer models) outputs wind and temperature at multiple levels. The
primary output of these forecasts is a gridded binary code format intended for use in flight planning
software.
There is no official wind and temperature aloft model for flight planning. Depending on the computer
model, the validity times, time intervals , and altitude levels will vary. Some models produce wind and
temperature forecasts at hourly time -steps while others produce forecasts at six-hour time steps. A few
models provide wind forecasts at 1,000-ft altitude levels while others are mostly at 3,000-ft altitude levels.
The data points (location) will also vary depending on the source.
Because each computer model is based on different algorithms and physics , the wind and temperature
forecasts will vary from model to model. These differences are due, in part, to the model’s forecast pressure
patterns on the surface and aloft. In addition, some models have more detailed terrain as well as finer
spacing between data points.
For many years there was just one set of wind and temperature forecasts, known as the FD Winds (then
later as the FB Winds), which were presented in a coded text table format (see Section 27.2.1.1.2).
Today’s flight planning software directly import s wind and temperature data from various computer
models, which has effectively made the coded text table format obsolete.
Although FB winds are still produced today, they are archaic compared with model output available to the
pilot and flight planner. FB winds:
• Are updated only four times daily, so winds that differ from the forecast are not updated for up to
six hours.
• Provide a single value for each of three broad periods of time: from issuance time through seven
hours, seven hours through 16 hours, and 16 hours through 28 hours.
• Provide a value at scattered locations in the country separated by about 100 to 150 mi.
Chapter 27, Forecasts 27-4
In contrast, for example, the NWS’ Rapid Refresh model winds:
• Are updated every hour based partly on automated wind reports from airliners.
• Provide a wind forecast for each hour into the future.
• Provide values at grid points separated by as low as 9 SM.
This section describes the details of the FB Wind and Temperature Aloft Forecast product. Other sections
within this handbook provide additional wind and temperature aloft forecasts (i.e., constant pressure level
forecasts [see Section 27.11.1) and the global wind and temperature forecasts provided under the WAFS
(see Section 27.8)].
27.2.1 FB Wind and Temperature Aloft Forecast
FB Wind and Temperature Aloft Forecasts are computer-prepared forecasts of wind direction, wind
speed, and temperature at specified times, altitudes, and locations.
27.2.1.1 FB Wind and Temperature Aloft Forecast Issuance
The NWS NCEP produces scheduled FB Wind and Temperature Aloft Forecasts four times daily for
specified locations in the CONUS, the Hawaiian Islands, Alaska and coastal waters, and the western Pacific
Ocean.
Amendments are not issued to the forecasts. Wind forecasts are not issued for altitudes within 1,500 ft of a
location’s elevation. Temperature forecasts are not issued for altitudes within 2,50 0 ft of a location ’s
elevation.
27.2.1.1.1 FB Wind and Temperature Aloft Forecast Text Format
The text format for the FB Wind and Temperature Aloft Forecast uses the symbolic form DDff+TT in
which DD is the wind direction (true), ff is the wind speed, and TT is the temperature.
Wind direction is indicated in tens of degrees (two digits) with reference to true north and wind speed is
given in knots (two digits). Light and variable wind or wind speeds of less than 5 kt are expressed by 9900.
Forecast wind speeds of 100 through 199 kt are indicated by adding 50 to the first two digits of the wind
direction and subtracting 100 from the speed. For example, a forecast of 250 °, 145 kt, is encoded as 7545.
Forecast wind speeds of 200 kt or greater are indicated as a forecast speed of 199 kt. For example, 7799 is
decoded as 270° at 199 kt or greater.
Temperature is indicated in degrees Celsius (two digits) and is preceded by the appropriate algebraic sign
for the levels from 6,000 through 24,000 ft. Above 24,000 ft, the sign is omitted since temperatures are
always negative at those altitudes.
The product header includes the date and time observations were collected, the forecast valid date and time,
and the time period during which the forecast is to be used.
27.2.1.1.2 FB Wind and Temperature Aloft Forecast Coding Example
Sample winds aloft text message:
DATA BASED ON 010000Z
VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 750252
Chapter 27, Forecasts 27-5
Sample message decoded:
DATA BASED ON 010000Z
Forecast data is based on computer forecasts generated the 1st day of the month at 0000 UTC.
VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000
The valid time of the forecast is the 1st day of the month at 0600 UTC. The forecast winds and
temperatures are to be used between 0500 and 0900 UTC. Temperatures are negative above 24,000 ft.
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
FT indicates the altitude of the forecast.
MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 750252
MKC indicates the location of the forecast. The rest of the data is the wind and temperature aloft forecast
for the respective altitudes.
Table 27-1 shows data for Kansas City, MO (MKC). Table 27-2 provides the time periods for the use of
FB Wind and Temperature Forecasts.
Table 27-1. Wind and Temperature Aloft Forecast Decoding Examples
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 550252
Altitude (ft) Coded Wind Temperature (˚C)
3,000 ft 9900 Light and variable Not forecast
6,000 ft 1709+06 170° at 9 kt +06 °C
9,000 ft 2018+00 200° at 18 kt Zero °C
12,000 ft 2130-06 210° at 30 kt -06 °C
18,000 ft 2242-18 220° at 42 kt -18 °C
24,000 ft 2361-30 230° at 61 kt -30 °C
30,000 ft 247242 240° at 72 kt -42 °C
34,000 ft 258848 250° at 88 kt -48 °C
39,000 ft 750252 250° at 102 kt -52 °C
Chapter 27, Forecasts 27-6
Table 27-2. Wind and Temperature Aloft Forecast Periods
Model
Run
Product
Available
6-Hour Forecast 12-Hour Forecast 24-Hour Forecast
Valid For Use Valid For Use Valid For Use
0000Z ~0200Z 0600Z 0200-0900Z 1200Z 0900-1800Z 0000Z 1800-0600Z
0600Z ~0800Z 1200Z 0800-1500Z 1800Z 1500-0000Z 0600Z 0000-1200Z
1200Z ~1400Z 1800Z 1400-2100Z 0000Z 2100-0600Z 1200Z 0600-1800Z
1800Z ~2000Z 0000Z 2000-0300Z 0600Z 0300-1200Z 1800Z 1200-0000Z
27.3 Graphical FB Wi nd and Temperature Aloft Forecast
Graphical depictions of FB Wind and Temperature Aloft Forecasts vary depending on the website. Details
and information on these graphical depictions can usually be found on the website ’s help or information
page.
27.4 Terminal Aerodrome Forecast (TAF)
A TAF is a concise statement of the expected meteorological conditions significant to aviation for a
specified tim
e period within 5 SM of the center of the airport ’s runway complex (terminal). TAFs use the
same weather codes found in METARs (see Section 24.3). Temperature is not included in the NWS TAF,
operators may use temperature information from the LAMP/MOS product (see Section 27.16).
27.4.1 TAF Responsibility
TAFs are issued by NWS WFOs fo r nearly 70 0 U.S. airpo rts. The majority of TAFs provide a 24-hour
forecast for the airport, while TAFs for some major airports provide a 30-hour forecast.
27.4.2 Generic Format of the Forecast Text of an NWS-Prepared TAF.
See Table 27-3 for the generic format of the NWS’ TAFs.
Chapter 27, Forecasts 27-7
Table 27-3. Generic Format of the National Weather Service’s TAFs
TAF
or
TAF AMD
or
TAF COR
Type of report
CCCC YYGGggZ Y1Y1G1G1/Y2Y2G2G2 dddffGfmfmKT
Location identifier Date/time of forecast
origin group
Valid period Wind group
VVVV w’w’
or
NSW
NsNsNshshshs
or
VVhshshs
or
SKC
WShwshwshws/dddftKT
Visibility group Significant weather
group
Cloud and vertical
obscuration groups
Non-convective LLWS group
TTGGgg
Forecast change
indicator groups
FMY1Y1GGgg TEMPO Y1Y1GG/YeYeGeGe PROB30 Y1Y1GG/YeYeGeGe
From group Temporary group Probability group
27.4.2.1 Type of Report (TAF, TAF AMD, or TAF COR)
The report-type header always appears as the first element in the TAF and is produced in three forms: a
routine forecast (TAF), an amended forecast (TAF AMD), or a corrected forecast (TAF COR).
TAFs are amended whenever they become, in the forecaster ’s judgment, unrepresentative of existing or
expected conditions, particularly regarding those elements and events significant to aircraft and airports.
An amended forecast is identified by TAF AMD (in place of TAF) on the first line of the forecast text.
Select airports have amendments routinely issued. See Table 27-7.
Chapter 27, Forecasts 27-8
27.4.2.2 Location Identifier (CCCC)
After the line containing either TAF, TAF AMD, or TAF COR, each TAF begins with its four-letter ICAO
location identifier.
Examples:
KDFW Dallas-Fort Worth
PANC Anchorage, Alaska
PHNL Honolulu, Hawaii
27.4.2.3 Date/Time of Forecast Origin Group (YYGGggZ)
The date/time of the forecast origin group (YYGGggZ) follows the terminal’s location identifier. It contains
the day of the month in two digits (YY) and the time in four digits (GGgg in hours and minutes) in which
the forecast is completed and ready for transmission, with a Z appended to denote UTC. This time is entered
by the forecaster. A routine forecast, TAF, is issued 20 to 40 minutes before the beginning of its valid
period.
Examples:
061737Z
The TAF was issued on the sixth day of the month at 1737 UTC.
121123Z
The TAF was issued on the 12th day of the month at 1123 UTC.
27.4.2.4 Valid Period (Y1Y1G1G1/Y2Y2G2G2)
The TAF valid period (Y1Y1G1G1/Y2Y2G2G2) follows the date/time of the forecast origin group. Scheduled
24- and 30-hour TAFs are issued four times per day, at 0000, 0600, 1200, and 1800Z. The first two digits
(Y1Y1) are the day of the month for the start of the TAF. The next two digits ( G1G1) are the starting hour
(UTC). Y2Y2 is the day of the month for the end of the TAF, and the last two digits ( G2G2) are the ending
hour (UTC) of the valid period. A forecast period that begins at midnight UTC is annotated as 00. If the
end time of a valid period is at midnight UTC, it is annotated as 24. For example, a 00Z TAF issued on the
9th of the month and valid for 24 hours would have a valid period of 0900/0924.
Whenever an amended TAF ( TAF AMD) is issued, it supersedes and cancels the previous TAF. That is,
users should not wait until the start of the valid period indicated within the TAF AMD to begin using it.
Examples
1512/1612
The TAF is valid from the 15th day of the month at 1200 UTC until the 16th day of the month at 1200 UTC.
2306/2412
This is a 30-hour TAF valid from the 23rd day of the month at 0600 UTC until the 24 th day of the month
at 1200 UTC.
0121/0218
Chapter 27, Forecasts 27-9
This is an amended TAF valid from the 1st day of the month at 2100 UTC until the second day of the month
at 1800 UTC.
0600/0624
This TAF is valid from the sixth day of the month at 0000 UTC until the sixth day of the month at 2400
UTC (or seventh day of the month at 0000 UTC).
27.4.2.5 Wind Group (dddffGfmfmKT)
The initial time period and any subsequent “from” (FM) groups begin with a mean surface wind forecast
(dddffGfmfmKT) for that period. Wind forecasts are expressed as the mean three -digit direction
(ddd, relative to true north) from which the wind is blowing, rounded to the nearest 10°, and the mean wind
speed in knots (ff) for the time period. If wind gusts are forecast (gusts are defined as rapid fluctuations in
wind speeds with a variation of 10 kt or more between peaks and lulls), they are indicated immediately after
the mean wind speed by the letter G, followed by the peak gust speed expected. KT is appended to the end
of the wind forecast group. Any wind speed of 100 kt or more will be encoded in three digits. Calm winds
are encoded as 00000KT.
The prevailing wind direction is forecast for any speed greater than or equal to 7 kt. When the prevailing
surface wind direction is variable (variations in wind direction of 30° or more), the forecast wind direction
is encoded as VRBffKT. Two conditions where this can occur are very light winds and convective activity.
Variable wind direction for very light winds must have a wind speed of 1 to 6 kt inclusive. For convective
activity, the wind group may be encoded as VRBffGfmfmKT, where Gfmfm is the maximum expected wind
gusts. VRB is not used in the non-convective LLWS group.
Squalls are forecast in the wind group as gusts ( G) but must be identified in the significant weather group
with the code SQ.
Examples:
23010KT
Wind from 230° “true” (southwest) at 10 kt.
28020G35KT
Wind from 280° “true” (west) at 20 kt gusting to 35 kt.
VRB05KT
Wind variable at 5 kt.
VRB15G30KT
Wind variable at 15 kt gusting to 30 kt due to forecast convective activity.
00000KT
Wind calm.
27.4.2.6 Visibility Group (VVVV)
The initial time period and any subsequent FM groups include a visibility forecast (VVVV) in statute miles
appended by the contraction SM.
When the prevailing visibility is forecast to be less than or equal to 6 SM, one or more significant weather
groups are included in the TAF. However, drifting dust ( DRDU), drifting sand ( DRSA), drifting snow
(DRSN), shallow fog (MIFG), partial fog ( PRFG), and patchy fog ( BCFG) may be forecast with
prevailing visibility greater than or equal to 7 SM.