What is the Winds and Temperatures Aloft Forecast (FB Winds) and what information does it provide?

The Winds and Temperatures Aloft Forecast, commonly called the FB Winds forecast, is an FAA weather product that gives pilots predicted wind direction, wind speed, and temperature at specific pressure altitudes ranging from 3,000 feet MSL up to 53,000 feet MSL. The forecast is issued four times daily and is available for look-ahead periods of 6, 12, and 24 hours. Pilots use this information to select the most favorable cruising altitude, calculate fuel burn, and estimate groundspeed and flight time.

How do you read the wind and temperature data in an FB Winds forecast?

FB Winds data is encoded in a four-digit group for winds and a separate two-digit temperature value; for example, '2321-04' means winds from 230 degrees at 21 knots with a temperature of negative 4 degrees Celsius. When the wind speed appears as '9900,' it indicates light and variable winds of less than 5 knots. Temperatures are always in Celsius, and the minus sign is omitted for altitudes at and above 24,000 feet MSL because temperatures there are always negative, as explained in the Aviation Weather Handbook (FAA-H-8083-28).

Why are winds and temperatures aloft important for pilot flight planning?

Knowing predicted winds aloft allows pilots to choose altitudes that offer tailwinds for better groundspeed and fuel efficiency, or to avoid strong headwinds that increase flight time and fuel consumption. Temperature data is equally critical because it helps pilots assess density altitude, the risk of carburetor icing, and the potential for airframe icing near the freezing level. The Aeronautical Information Manual (AIM) and the Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25) both emphasize using FB Winds forecasts as a key step in preflight weather planning.

Winds and Temperatures Aloft Forecast (FB Winds)

Before every cross-country flight, a smart pilot asks: which altitude will give me the best tailwind, the smoothest air, and the most favorable temperature for engine performance? The Winds and Temperatures Aloft Forecast — officially abbreviated FB (formerly called the FD winds) — is the product designed to answer exactly those questions. Issued by the Aviation Weather Center (AWC), the FB forecast provides computer-generated predictions of wind direction, wind speed, and free-air temperature at a series of standard altitudes across the United States. Understanding how to decode and use the FB is both a knowledge-test requirement and an essential practical skill for every cross-country flight.

This article walks you through where the FB comes from, how to decode the compact coded format, what the numbers mean in the cockpit, and the traps the FAA loves to put on the written exam.

What the FB Forecast Contains

The FB is issued four times daily, based on radiosonde balloon observations and numerical weather models. Each issuance covers a specific valid time window, and the forecast is tied to a particular valid time — the period during which you should use the data for actual flight planning. The header of each FB table tells you the date and time of the data source (when the observations were taken), the time the forecast was issued, and the valid time. For planning purposes, you should select the FB issuance whose valid time most closely matches your planned departure or en route time.

The altitudes covered by the standard FB forecast are: 3,000; 6,000; 9,000; 12,000; 18,000; 24,000; 30,000; 34,000; and 39,000 feet MSL. Higher-altitude products extend to 45,000 and 53,000 feet, but for private pilot training, the altitudes up through 12,000 and 18,000 feet are most relevant. The forecast is organized in columns by altitude and rows by geographic location (reporting station or grid point).

How to Decode the Coded Format

The FB uses a compact four- or six-digit code for each altitude entry. Once you crack the code, it becomes straightforward to read. Here is the basic structure:

First two digits: Wind direction in tens of degrees (true north reference). Divide by 10 to get the actual direction. For example, a code of 23 means 230°.
Second two digits: Wind speed in knots. For example, 2318 means winds from 230° at 18 knots.
Last two digits (with sign): Temperature in degrees Celsius. A plus or minus sign may be shown; at and below 24,000 feet, a minus sign is always listed explicitly. Above 24,000 feet, temperatures are always negative, so the minus sign is omitted by convention — you are expected to know temperatures are below zero at those altitudes.

A full entry might look like this: 2318-04. Decode it as: winds from 230° true at 18 knots, temperature −4°C. Another example: 9900+00 — the special code 9900 means light and variable winds (less than 5 knots), and the temperature is +0°C (essentially 0°C). When you see 9900, there is no usable wind direction or speed information for that altitude and location.

The High-Wind Speed Encoding Trick

Here is where one of the most notorious exam traps hides. When wind speeds are 100 knots or greater, the direction code is encoded by adding 50 to the direction digits, and the speed digits are reduced by 100 knots (with the coder aware that the resulting speed value is understood to represent speeds of 100 knots and above). For example, if the actual wind is 270° at 105 knots, the direction digits become 27 + 50 = 77, and the speed digits become 105 − 100 = 05. So the encoded entry would be 7705. To decode: 77 − 50 = 27 → 270°, and 05 + 100 = 105 knots. Whenever you see a direction code of 51 or greater, apply this rule. This encoding allows the format to stay within two digits for both direction and speed while still conveying high wind values accurately.

True vs. Magnetic Direction

This distinction is critically important in practical use. All wind directions in the FB forecast are given in degrees TRUE, not magnetic. Winds reported by air traffic control and ATIS, on the other hand, are in degrees magnetic. When using FB winds for flight planning — particularly for calculating true course corrections and groundspeed — you will work in the true reference frame, which is consistent with how courses are plotted on a sectional chart. If you need to mentally picture the wind versus your compass heading, remember to apply magnetic variation before comparing.

No Forecast Below 1,500 Feet AGL

The FB does not include wind forecasts for the 3,000-foot level if that altitude is within 1,500 feet of the station elevation. In other words, for high-elevation airports such as those in mountainous regions, the lowest relevant altitude entry will simply be blank or omitted. This makes physical sense — the FB represents free-air (upper air) conditions, not surface conditions. For surface and low-altitude wind information, you would consult the Terminal Aerodrome Forecast (TAF), the METAR, or the Area Forecast Discussion.

Why the FB Forecast Matters for Flight Planning

The FB is far more than an academic exercise. Here are the major ways pilots use it in the real world:

Altitude selection: Comparing wind direction and speed at different altitudes lets you choose the level that provides the best groundspeed — a tailwind component on a long cross-country can mean the difference between arriving with comfortable reserves or landing short.
Turbulence and wind shear awareness: When wind speeds vary dramatically between adjacent altitude levels, the large gradient can indicate mechanical turbulence or wind shear. Choosing an altitude where winds are steadier and lighter often means a smoother ride.
Density altitude and engine performance: The forecast temperature at cruise altitude lets you calculate density altitude, which directly affects true airspeed, aircraft performance, and — if you are flying a normally aspirated engine — the power available. Knowing you will be at −10°C at 9,000 feet versus +5°C changes your performance calculations meaningfully.
Icing awareness: While the FB does not directly forecast icing, knowing the temperature at altitude helps you assess whether visible moisture (clouds, precipitation) combined with that temperature puts you in the icing range (roughly 0°C to −20°C is most hazardous). A temperature of just below 0°C at your planned altitude, combined with a visible moisture forecast, is a red flag to investigate further with PIREPs and AIRMETs.
Fuel planning: Groundspeed drives fuel consumption in terms of range. Accurate wind information from the FB helps you calculate time en route and therefore total fuel burn with much greater precision than assuming calm winds.

Key Numbers and Rules

FB forecasts are issued four times daily (approximately 0000Z, 0600Z, 1200Z, 1800Z issuance cycles).
Standard altitudes: 3,000 through 39,000 feet MSL in the basic FB product.
Wind directions are true north reference — not magnetic.
Code 9900 = light and variable winds (less than 5 knots).
Direction codes of 51–86 indicate winds of 100 knots or greater; subtract 50 from direction, add 100 to speed to decode.
The 3,000-foot level is omitted if it is within 1,500 feet of the station elevation.
Temperatures above 24,000 feet are always negative; the minus sign is omitted by convention at those levels.
Use the FB issuance whose valid time most closely matches your planned flight time.

Common Test Traps

Forgetting true vs. magnetic: The FAA loves to ask which direction is reported in the FB — the answer is always true. Do not confuse this with ATIS or tower winds, which are magnetic.
Missing the high-wind encoding: If you see a direction code above 50, many students try to treat it as a normal direction and get a nonsensical answer like winds from 720°. Always check: is the first two-digit group greater than 36? If so, apply the add-50-to-direction/add-100-to-speed rule.
Ignoring the valid time: Students sometimes grab the most recently issued FB without checking whether its valid time matches their flight. An FB issued at 0600Z but valid for 1200Z conditions should be used for a flight departing around noon Zulu, not a flight departing at 0700Z.
Assuming a temperature sign above 24,000 feet: Temperatures at FL240 and above carry no minus sign in the coded format, but they are always negative. A student who reads the digits as a positive temperature will make a significant density altitude calculation error.
Confusing 9900 with calm winds: The code 9900 means light and variable, not necessarily calm (zero knots). The actual wind could be up to about 4 knots from any direction. This matters for groundspeed calculations — you cannot assume exactly zero wind.

Mastering the FB winds forecast is one of those skills that pays dividends every time you fly cross-country. Once you can quickly scan a table, decode the entries, compare altitudes, and check the valid time, you have a powerful planning tool that directly improves both safety and efficiency in the air.