The Winds and Temperatures Aloft Forecast, the Coded FB Table, and Why Nine Nine Zero Zero Means Dead Calm

The winds and temperatures aloft forecast (the FB) predicts wind direction, wind speed, and temperature at fixed altitudes so you can plan a cross-country around the air you’ll actually fly in - not the calm you feel on the ramp. A standard six-digit group like 2420-04 reads as wind from 240° true at 20 knots, temperature -4°C, while the special code 9900 means light and variable (wind under 5 knots). Master it and you’ll pick altitudes that save time and fuel instead of burning both.

What is the winds and temperatures aloft forecast?

The wind on the ground is not the wind you fly in. You can stand on the ramp under a limp windsock, climb to 6,000 feet, and find a 30-knot headwind that stretches a two-hour leg into three - on two hours of planned fuel. That gap has ended more cross-countries in a farmer’s field than almost anything else.

The FB closes that gap. It’s a forecast produced by the National Weather Service through the Aviation Weather Center, giving predicted wind direction, wind speed, and temperature at a series of standard altitudes.

Those altitudes are fixed: 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, and on up to 39,000 feet for aircraft in the flight levels. For training flights, the ones that matter most are 3,000, 6,000, and 9,000 feet.

How do I read a winds aloft forecast group?

At each altitude you get a small group of digits - usually six. Take 2420-04 and read it in pieces:

• First two digits - wind direction. “24” means 240 degrees. The trailing zero is dropped to save space, so you read the value in tens of degrees.
• Next two digits - wind speed in knots. “20” means 20 knots.
• Last two digits with the sign - temperature in Celsius. “-04” means 4 degrees below zero.

So 2420-04 means the wind is forecast from 240° at 20 knots, temperature -4°C. Direction, speed, temperature - once you see the pieces, you can’t un-see them.

Is winds aloft direction true or magnetic?

Wind direction in the FB is referenced to true north - not magnetic north. This is a favorite examiner question.

Almost everything else in your flying life is magnetic: your heading indicator, the runway numbers, the winds the tower reads you. But the winds aloft forecast is true, which is exactly what you want for your navigation log, because you build that log in true as well.

The trap is mixing frames. Don’t pull a true wind direction and compare it directly against a magnetic heading and expect it to make sense. True for the winds aloft, magnetic for what you see out the window and on the panel - and you’re the translator between the two worlds.

What does 9900 mean in a winds aloft forecast?

9900 is the code for light and variable - wind forecast at less than 5 knots with no reliable direction. It does not mean 990 degrees at zero knots, which is impossible anyway since a compass only reads to 360.

When you see 9900, you can stop worrying about wind correction at that altitude. The air is essentially sitting still.

How are strong winds coded in the FB?

Wind speeds in the forecast run only up to 199 knots, but the group has just two digits for direction and two for speed - and two digits of speed only reach 99. So there’s a trick for encoding a wind of, say, 119 knots.

When the wind speed is 100 knots or more, add 50 to the direction number and subtract 100 from the speed number. The flag is the direction: if the first two digits are greater than 36, something’s up, because a real direction can’t exceed 360 degrees.

Take 7319. Direction reads “73,” which is impossible - so the code is in play. Subtract 50: 73 − 50 = 23, so the direction is 230 degrees. Add 100 to the speed: 19 + 100 = 119 knots. That’s 230° at 119 knots, a serious jet-stream wind you’ll see way up high.

You won’t fly a Cessna 172 in a 119-knot wind, but an examiner may hand you a printout with a level coded this way. Reading it correctly - or getting confused - tells them whether you understand the product or just memorized one example. The Airman Certification Standards (ACS) expect you to obtain and correctly interpret aviation weather, then use it to make a decision - not just read numbers.

Why are some altitudes and temperatures missing?

Two quirks trip up new pilots:

No forecast within 1,500 feet of station elevation. If a reporting station sits at 4,000 feet elevation, a 3,000-foot forecast would be underground and a 6,000-foot forecast is only 2,000 feet up. So for high-elevation stations, the lower groups simply aren’t published - don’t hunt for a number that was deliberately left out.

No temperature for the 3,000-foot level, or for any level within 2,500 feet of station elevation. That’s why a 3,000-foot group is often just four digits - direction and speed, no temperature. And above 24,000 feet the temperature is always negative, so the minus sign is dropped. If you see a flight-level temperature with no sign, it’s negative - always.

How do I use winds aloft to choose a cruising altitude?

Reading the code is a party trick until you use it to make the airplane do something smart. Picture a westbound cross-country, roughly 200 miles, in a trainer that trues out around 110 knots. You’re deciding between 6,000 and 9,000 feet, and you pull the FB for a point near your route:

• At 6,000 feet: 2720 → 270° at 20 knots
• At 9,000 feet: 2735 → 270° at 35 knots

You’re heading west, about 270 degrees, so at both altitudes the wind is right on the nose. That’s a 20-knot headwind at 6,000 and a 35-knot headwind at 9,000 - a 15-knot difference coming straight out of your groundspeed.

At 6,000 you might see about 90 knots across the ground; at 9,000, closer to 75 knots. Over 200 miles, that’s roughly 45 minutes and a real chunk of fuel. On this westbound leg, the forecast is telling you to stay lower.

Now fly the same route home eastbound the next day with similar winds. That 35-knot wind at 9,000 is suddenly a tailwind, and going high is the smart play. Same numbers, opposite decision - because the wind’s direction relative to your course flipped.

How accurate is the winds aloft forecast?

It’s a forecast - the atmosphere’s best guess about itself, and the atmosphere is under no obligation to cooperate. The FB can be off, sometimes badly, especially ahead of a front or in mountainous terrain where local flow does its own thing.

So you plan with the FB, then verify in the air. Check your groundspeed against your flight plan at the first checkpoint. If the forecast promised 90 knots and you’re seeing 70, the airplane is telling you the forecast was optimistic - time to recompute fuel and decide whether a planned fuel stop just became a required one.

One more practical point: check the valid time and forecast period. These are issued for specific windows, and the wind at 9 a.m. is not the wind at 3 p.m. Grab the forecast that covers the time you’ll actually fly the leg, not the one that was valid when you sat down at the computer.

Key Takeaways

• A standard FB group reads as direction / speed / temperature - e.g. 2420-04 is 240° true at 20 knots, -4°C.
• Winds aloft direction is true north, unlike almost everything else in the cockpit, which is magnetic.
• 9900 means light and variable (under 5 knots); a direction digit above 36 means the strong-wind code is in play - subtract 50 from direction, add 100 to speed.
• Expect missing levels within 1,500 feet of station elevation and no temperatures within 2,500 feet of it (and none at 3,000 feet).
• Use the forecast to pick a fuel- and time-saving altitude, then confirm groundspeed at your first checkpoint and adjust.