Winds and Temperatures Aloft: How to Read an FB Forecast

Winds aloft decide your ground speed, your fuel, and often your altitude. The temperatures in the same forecast tell you where the freezing level sits. This page decodes the FAA Aviation Weather Handbook's sample FB forecast group by group, covers the rules that trip pilots up, and explains how the old coded table relates to the model winds in today's apps. The rules come from the Handbook and NWS Instruction 10-812, the directive the NWS follows to produce the forecast [1][2].

What is the FB winds and temperatures aloft forecast?

The Handbook's definition: "FB Wind and Temperature Aloft Forecasts are computer-prepared forecasts of wind direction, wind speed, and temperature at specified times, altitudes, and locations." [1, para. 27.2.1] No forecaster writes them by hand. The NWS National Centers for Environmental Prediction (NCEP) issues them four times daily for locations in the contiguous U.S., Hawaii, Alaska and coastal waters, and the western Pacific [1, para. 27.2.1.1].

Two rules shape what you see. "Amendments are not issued to the forecasts." And some levels are left blank on purpose: "Wind forecasts are not issued for altitudes within 1,500 ft of a location’s elevation." "Temperature forecasts are not issued for altitudes within 2,500 ft of a location’s elevation." [1, para. 27.2.1.1]

Which altitudes are forecast?

The standard bulletin covers 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 ft. NWS Instruction 10-812 adds 45,000 and 53,000 ft for selected locations, and extra low levels for Hawaii and the Pacific [2, sec. 4]. All levels are referenced to mean sea level (MSL), and all times are UTC [2, sec. 4]. The levels through 12,000 ft are actual altitudes; 18,000 ft and above are pressure altitudes tied to pressure surfaces, 18,000 ft to 500 hPa up to 39,000 ft at 200 hPa [2, sec. 4]. Between the printed levels and stations, "Forecasts for intermediate levels may be determined by interpolation." [2, sec. 4]

How do you read an FB forecast? A worked decode

A bulletin has a header and then one line per station. Here is the Handbook's sample, transcribed exactly from Section 27.2.1.1.2 of the FAA Aviation Weather Handbook [1, para. 27.2.1.1.2]. It is an official teaching example, not a live forecast. Hover, focus, or tap any group.

Scroll sideways to see the full line.

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

Official sample FB forecast, FAA Aviation Weather Handbook (FAA-H-8083-28B), Section 27.2.1.1.2 and Table 27-1 [1, para. 27.2.1.1.2].

Group by group. "Handbook meaning" is quoted exactly from FAA Aviation Weather Handbook 27.2.1.1.2 and Table 27-1; "Plain English" is ours, with the rule behind it cited.

Read as a whole: from the model run at 0000 UTC on the 1st, over Kansas City the wind is light and variable at 3,000 ft, then veers from 170° at 9 knots at 6,000 ft to 250° at 102 knots at 39,000 ft, while the temperature falls from plus 6°C to minus 52°C. The freezing level sits near 9,000 ft, where the forecast reads 0°C. A westbound airplane would find the lightest headwind down low; an eastbound jet would find a strong tailwind up high.

Source conflict, noted: the header row of the Handbook's Table 27-1 prints the last group as 550252, but the sample message two lines above prints 750252, and the table's own decode, 250° at 102 knots, only works for 750252 [1, para. 27.2.1.1.2]. This page uses 750252.

What are the decoding rules?

The whole code fits in six rules, from Handbook 27.2.1.1.1 and NWS Instruction 10-812 [1, para. 27.2.1.1.1][2, sec. 6]:

The 100-knot rule is the one that catches people. Any time the first two digits are 37 or more, the group can't be a normal direction, because 36 is 360°. Subtract 50 for the direction and add 100 to the speed. In the sample, 750252 becomes 250° at 102 knots [1, para. 27.2.1.1.2].

A second example: blank levels at mountain stations

NWS Instruction 10-812 shows the bulletin format with two Arizona stations [2, sec. 6.1]. It is a format example, not a live forecast:

Scroll sideways to see the full line.

FT 3000     6000     9000   12000   18000   24000 30000 34000 39000
PHX 0207 0611+13 0805+07 9900+02 2524-14 2535-27 248139 259647 269455
PRC               0507+05 9900+00 2516-16 2531-29 246942 257347 267353

Format example from NWS Instruction 10-812, Section 6.1 [2, sec. 6.1]. Spacing as printed.

Phoenix (PHX) starts at 3,000 ft with 0207, a wind of 020° at 7 knots and no temperature. Prescott (PRC) has nothing at 3,000 or 6,000 ft; its first group, 0507+05, is at 9,000 ft. That is the elevation rule at work: no wind within 1,500 ft of the station, no temperature within 2,500 ft [2, sec. 4]. Up high, PHX 248139 decodes as 240° at 81 knots, minus 39°C.

When is an FB forecast valid?

Three times sit in the header. DATA BASED ON is the model run. VALID is the time the forecast is centered on. FOR USE is the window to apply it [1, para. 27.2.1.1.2]. Each run produces 6-hour, 12-hour, and 24-hour forecasts. Handbook Table 27-2 lists them [1, para. 27.2.1.1.2]:

If the scheduled issue is late, "users should continue using the valid FB's based on 6-hour earlier data until NCEP transmits the new forecast." [2, sec. 7]

Source conflict, noted: the FOR USE windows don't match across FAA and NWS examples. The Handbook sample reads 0500 to 0900Z, Table 27-2 gives 0200 to 0900Z for the same 0600Z valid time, and the NWS Instruction 10-812 example gives 0600 to 1200Z [1, para. 27.2.1.1.2][2, sec. 6.1]. None is wrong for its own bulletin. Use the FOR USE line printed on the forecast in front of you, not a remembered window.

FB winds or model winds: which should you use?

The Handbook is blunt about the coded table. It says FB winds "are still produced today" but are "archaic compared with model output available to the pilot and flight planner" [1, para. 27.2]. Its reasons:

• "Are updated only four times daily, so winds that differ from the forecast are not updated for up to six hours."
• They give one value for each of three broad periods, and only at stations about 100 to 150 miles apart [1, para. 27.2].
• By contrast, the NWS Rapid Refresh model updates every hour, forecasts each hour ahead, and uses grid points as close as 9 statute miles [1, para. 27.2].

The same section adds context that matters. There is no single official wind and temperature model for flight planning. Each computer model has its own time steps, altitude levels, and data points, and "Because each computer model is based on different algorithms and physics, the wind and temperature forecasts will vary from model to model." "Today’s flight planning software directly imports wind and temperature data from various computer models, which has effectively made the coded text table format obsolete." [1, para. 27.2]

So the practical answer is both, with judgment. The model wind in your app is likely fresher and closer to your route. The FB table is a common reference that every briefer and tool can read. When they disagree by a lot, treat the wind as uncertain and plan fuel for the worse one. Graphical versions of the FB forecast also exist, but "Graphical depictions of FB Wind and Temperature Aloft Forecasts vary depending on the website." [1, para. 27.3] Read the site's legend.

Where the numbers come from: the Handbook says constant pressure level forecasts, such as the 500 mb or 300 mb charts, "are the source for wind and temperature aloft forecasts" [1, para. 27.11.1]. Its Table 27-14 puts 850 mb near 5,000 ft, 700 mb near 10,000 ft, 500 mb near 18,000 ft, and 300 mb near 30,000 ft MSL [1, para. 27.11.1.2].

In the cockpit, FIS-B also carries winds and temperatures aloft. The AIM lists that product's update interval as 12 hours, plus or minus 15 minutes, with a rebroadcast every 10 minutes [3, para. 7-1-9]. Check the valid time on whatever you're looking at.

How do you use winds aloft to plan a flight?

• Pick the right window. Match your departure and en route times to the FOR USE window of the forecast you're reading [1, para. 27.2.1.1.2].
• Interpolate between stations and levels. If your cruise altitude is 8,000 ft, read 6,000 and 9,000 ft and estimate between them [2, sec. 4].
• Remember true north. FB directions are true, like METAR winds; runway numbers and PIREP winds are magnetic. Correct before you compute a crosswind component [1, para. 27.2.1.1.1].
• Read the temperatures too. Where the sign flips between two levels, the freezing level is between them. The FAA icing guide notes "Freezing levels can be determined from the winds aloft forecast." [4, para. 4-1g] The dedicated freezing level graphics are more precise (icing guide).
• Watch the trend with height. A fast increase in wind speed or a change in direction between levels can mean wind shear and turbulence; compare with turbulence forecasts and PIREPs.
• Plan fuel for the worse case. The forecast can be wrong for up to six hours before the next issue [1, para. 27.2].

Where is the official FB format?

Where do winds aloft forecasts mislead pilots?

• They are averages. One value per station per period, with stations about 100 to 150 miles apart. Local effects near mountains and fronts fall between them [1, para. 27.2].
• No amendments. A forecast that's wrong stays wrong until the next issue [1, paras. 27.2 and 27.2.1.1].
• High stations look empty. A blank at 3,000 or 6,000 ft isn't calm air; it's the elevation rule [1, para. 27.2.1.1].
• Mixed-up units. Direction is true and in tens of degrees, speed is knots, temperature is Celsius [1, para. 27.2.1.1.1].

How do you use winds aloft in a go/no-go decision?

The decision is yours as pilot in command. Winds aloft rarely ground a flight alone, but they change the plan: a headwind can turn a nonstop into a fuel stop, and a strong wind over ridges hints at mountain wave. Compare the forecast wind with what you actually see in flight, and give a PIREP when they differ. Record your assumptions in a FRAT [5, ch. 3].

Where do winds aloft fit in a disciplined decision?

PlaneWX is decision support for general aviation pilots, built around one idea: "Fly like it's your job." Treat the weather decision the way a professional crew would, with the same process every time. That process is a loop: Brief, then FRAT, then Fly or Stay, then Debrief, with a Mentor if you want one. Winds aloft feed the Brief. Here's how PlaneWX handles them, as described in the help center [6]:

• Brief: the Winds Aloft card. It uses model winds, not FB winds: "PlaneWX replaces these with route-specific, model-derived winds sampled directly along your flight path." On U.S. routes the models are HRRR, GFS, and ECMWF, averaged as vectors at each route point (Winds Aloft).
• Brief: when models disagree. The help center is candid: "When models disagree significantly about wind speed or direction, the consensus may understate the true wind." The Weather Sources tab shows each model side by side with an agreement label (Winds Aloft).
• Brief: altitude choice. The Altitude Advisor, a PlaneWX Labs feature for Pro Plus and Enterprise, samples FB bulletins from stations along the route and picks the 6, 12, or 24-hour forecast by departure time. Its own limits section says "Winds aloft are from FB bulletins. These are issued every 6 hours and represent a snapshot." (Altitude Advisor)
• FRAT. The flight risk assessment opens within 4 hours of departure, and your own ratings drive it (FRAT).
• Fly or Stay. "PlaneWX never recommends GO or NO-GO. You make the call as PIC." (The Risk Loop)
• Debrief. After the flight, compare the forecast winds with what you saw. Self Debrief is a PlaneWX Labs feature for Pro Plus (The Risk Loop).

The help center is plain about the limits: "PlaneWX is not a substitute for a complete, independent pre-flight weather briefing. Pull one from a source you already trust before you fly." (The Risk Loop)

See the winds along your next route in a PlaneWX briefing, or read how PlaneWX computes route winds. Related: the Altitude Advisor and the PlaneWX guide to planning mountain route weather.

This page explains published FAA and NWS guidance. The forecasts shown are official teaching and format examples from the FAA Aviation Weather Handbook and NWS Instruction 10-812, not live forecasts. Always get a current briefing before you fly.