The Winds and Temperatures Aloft Forecast, Cracking the Coded FB Line, and How Nine Nine Zero Zero Means Calm Air While Seven Seven Five One Hides a Hundred-Knot Wind

The Winds and Temperatures Aloft Forecast - the product old-timers call the FD and the National Weather Service now labels FB - is a coded, six-digit line that tells you wind direction, wind speed, and temperature at standard cruise altitudes. Read it correctly and 9900 means light-and-variable, near-calm air, while 7751 hides a 151-knot jet-stream wind. It is the only product in a standard briefing that describes the air where you’ll actually spend the whole flight.

What Is the Winds and Temperatures Aloft (FB) Forecast?

The FB is a computer-model forecast, not an observation - nobody is up there measuring. The Weather Prediction Center issues it a few times a day, valid for specific times, for a list of specific stations across the country.

Each station gets a row, with columns for standard altitudes: 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, and on up to 39,000 feet and higher.

Your METAR and TAF describe the surface and the terminal area - what the weather is doing where the airplanes park. The FB is the only briefing product that tells you what the air is doing at your cruise altitude. That drives your fuel burn, true airspeed, groundspeed, icing risk, and whether you reach your destination with legal reserves.

The Airman Certification Standards (ACS) list interpreting the winds and temperatures aloft under cross-country planning. On a checkride, when the examiner hands you a briefing and asks you to plan a route, this is a product you’re expected to pull apart and use - not just glance at.

Which Altitudes and Temperatures Are Missing, and Why?

Two gaps trip people up, and both are intentional:

• No wind is forecast within 1,500 feet of a station’s ground elevation. If your departure airport sits at 5,000 feet in the mountains, there is no 3,000-foot wind for that station - it’s below the ground.
• No temperature is forecast for the 3,000-foot level, or within 2,500 feet of the station elevation. The low-level air is too influenced by the surface to bother forecasting.

If a number isn’t there, it isn’t missing by accident - don’t go looking for it.

How Do I Read the Six-Digit Winds Aloft Code?

A basic group is six digits, such as 2415+07. Break it into three pieces:

1. First two digits - wind direction in tens of degrees, referenced to true north (not magnetic). Add a zero back on the end. So 24 = 240°, 18 = 180°, and 36 = 360° (straight out of the north).
2. Next two digits - wind speed in knots. So 15 = 15 knots.
3. Last group with a sign - temperature in degrees Celsius. So +07 = +7 °C.

Read together, 2415+07 means wind from 240° true at 15 knots, temperature +7 °C.

One freebie: above 24,000 feet the temperature sign is dropped, because it’s always below zero up there. At 30,000 feet, a temperature group with no sign is negative - every time.

How Do I Decode a Wind of 100 Knots or More?

This is the trick that unlocks the whole product. When a wind is 100 knots or faster, a three-digit speed won’t fit in two columns. So the forecast adds 50 to the direction as a flag.

To decode it:

1. Look at the first two digits. A direction can never exceed 360°, so any first pair greater than 36 is your flag that this is a high-wind code.
2. Subtract 50 from the direction digits.
3. Add 100 to the two-digit speed.

Work the title example, 7751:

• 77 is greater than 36 - flag is up.
• 77 − 50 = 27, so the direction is 270° true (out of the west).
• Speed 51 + 100 = 151 knots.

So 7751 is a wind from 270° true at 151 knots - a jet stream, a river of air faster than most light aircraft will ever fly. (The title’s “+05” was simplified to teach the decode; at true jet-stream altitudes you’d actually see a deeply negative temperature, something like −56 °C. The lesson is the wind: direction over 36, subtract 50, add 100 to the speed.)

What Does 9900 Mean?

9900 is the code for light and variable. It is not a wind from 990° at 0 knots - that would be nonsense on two counts. It means the wind is less than 5 knots with no meaningful direction to report. Calm-ish, easy air.

Put the two extremes side by side: 9900 means the air is asleep; 7751 means a 151-knot freight train. Nearly identical-looking digits, completely opposite worlds - read the code wrong and you’d never know the difference.

How Do I Use the Winds Aloft to Pick a Cruise Altitude?

Decoding is a party trick until you use it to make a decision. The FB lets you shop for altitude.

Picture a Cessna 172 with a true airspeed near 110 knots, flying west into the prevailing wind. Westbound VFR uses even thousands plus 500 (6,500, 8,500, and so on). You pull the winds for a station near your route:

• 6,000 ft reads 2720 - 270° at 20 knots. That’s a 20-knot headwind on the nose.
• 9,000 ft reads 3135 - 310° at 35 knots. The wind has turned and strengthened - a 35-knot headwind, mostly on the nose.

The lesson: going west today, lower is better. Wind generally increases with altitude, so climbing high would drag your groundspeed into the 70s and burn your reserves.

Now fly home the next day, eastbound, using odd thousands plus 500 (7,500, 9,500). That same west wind is now on your tail. You want to be high, in the strongest wind you can find - a 35-knot tailwind on a 110-knot airplane is 145 knots across the ground. That’s landing with fuel and daylight to spare.

The rule of thumb: headed into the wind, fly low; riding the wind, climb up and grab it. Four digits and the right altitude can save you 20–30 knots of groundspeed.

How Do I Find the Freezing Level and Icing Risk?

Watch the temperature column for where it crosses zero.

If 6,000 ft reads +04 and 9,000 ft reads −02, the air passes through freezing somewhere between 6,000 and 9,000 feet. That band is your freezing level. With any visible moisture - clouds or precipitation - the layer from the freezing level on up is where structural icing lives.

A VFR pilot with clouds at 8,000 and sub-freezing temps by 9,000 now knows exactly which layer to avoid. An instrument pilot considering a climb through a layer has just found the altitude where ice becomes the conversation - all from numbers most people skip.

How Can the Forecast Warn Me About Turbulence?

Look at how the wind changes between adjacent altitudes.

If 3,000 ft reads 2410 and 6,000 ft reads 2735, the direction swung 30° and the speed more than tripled over just 3,000 feet. That steep gradient is wind shear - the setup for a choppy ride and possible mechanical turbulence.

When the numbers change smoothly from one level to the next, expect a smoother ride. When they jump hard, brace for it and brief your passengers before they turn green.

Key Takeaways

• The FB (winds and temperatures aloft) forecast is the only briefing product that describes your cruise - stop skipping it.
• Read six digits as direction (tens of degrees, true north) + speed (knots) + temperature (°C).
• If the first two digits exceed 36, subtract 50 from the direction and add 100 to the speed - so 7751 = 270° at 151 knots.
• 9900 means light and variable (under 5 knots); above 24,000 feet an unsigned temperature is always negative.
• Fly low into a headwind, high with a tailwind, use the temperature column to locate the freezing level, and watch level-to-level changes to anticipate turbulence.