The Winds and Temperatures Aloft Forecast, the Nine Nine Zero Zero Code, and Reading the One Line That Tells You Which Altitude Will Actually Get You There

The winds and temperatures aloft forecast - the text product headed FB, often just called “the winds aloft” - is the one line in your weather briefing that tells you whether your chosen cruise altitude will help you or punish you. It’s a National Weather Service model forecast that packs wind direction, wind speed, and temperature for a series of standard altitudes into a short string of digits. Read it correctly, and you pick your altitude on purpose instead of guessing.

Two pilots can leave the same airport, in the same airplane, on the same morning, headed the same way. One reads this forecast and one guesses. Forty-five minutes later, one is making a groundspeed of 140 knots while the other crawls along at 95, watching fuel disappear. The only difference was one line in a briefing.

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

The product is officially the Winds and Temperatures Aloft Forecast. In the older text format it carries the header FB, and many pilots still call it “the winds aloft” or “the FB.”

It’s produced by the National Weather Service, and it is a forecast, not an observation. Nobody is up there measuring this in real time - a computer model is predicting what the wind and temperature will do at standard altitudes, over a specific station, for a specific valid time.

That last point matters more than most students realize. This is a forecast for a point in time, over a point on the ground. Each product has valid periods, and you want the one that lines up with when you’ll actually be enroute. Grab the wrong valid time and you’re planning with numbers for six hours from now.

How Do I Decode a Winds Aloft Forecast?

A station’s line lists altitudes across the top - 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000 feet, and on up. Under each altitude sits a clump of numbers like 2426+03.

Break it into three parts:

• First two digits - wind direction. “24” means 240 degrees.
• Second two digits - wind speed in knots. “26” means 26 knots.
• Last group - temperature in degrees Celsius. “+03” means +3°C.

So 2426+03 decodes to wind from 240 degrees true at 26 knots, +3°C.

One detail pilots miss: winds aloft are always given in true direction, not magnetic. That’s the opposite of the wind the tower reads you in the pattern, which is magnetic. The upside is that your groundspeed and heading math is already in true, which lines up nicely with your true course.

At the higher levels, above 24,000 feet the temperature sign is dropped because it’s always below zero up there. If you see a high-altitude temperature with no sign, it’s negative - always.

Why Are Some Altitudes Blank on the Forecast?

Near the surface, some boxes are simply empty. There’s a rule behind it worth memorizing:

• No wind is forecast for an altitude within 1,500 feet of the station’s elevation.
• No temperature is forecast within 2,500 feet of the station’s elevation.

Down close to the ground, the wind is a mess - bent and dragged by terrain, surface friction, and heating. A smooth model forecast at that height would be misleading, so the NWS leaves it blank rather than hand you a number it doesn’t trust.

Practical takeaway: if you’re planning a short, low hop and the only applicable altitude is blank, that’s the forecast telling you it can’t help you down there. Lean harder on the surface observations - the METARs, the terminal forecasts (TAFs), and your own eyes.

What Does 9900 Mean in a Winds Aloft Forecast?

Read down a column and you may hit a group that reads 9900. It is not a wind from 990 degrees - there’s no such thing on the compass.

9900 is the code for light and variable. It means the wind is forecast to be less than 5 knots with no dominant direction worth reporting. That altitude is calm: the wind won’t help you and won’t hurt you. On a hot summer day, that can be the smoothest air in the column.

How Do I Decode Winds of 100 Knots or More?

The model has a problem when the wind gets fast: speed only gets two digits, so the largest number it could print is 99 knots. But winds at flight levels can scream past 100, 120, even 150 knots in a good jet stream.

The trick: when the wind is 100 knots or more, add 50 to the direction and subtract 100 from the speed before coding it. To decode, reverse it.

Take the group 731960:

1. Direction “73” is greater than 36, which is impossible for a compass heading. That’s your flag that the strong-wind code is in play. Subtract 50: 73 − 50 = 23, so the direction is 230 degrees.
2. Speed “19” - add 100 back: 19 + 100 = 119 knots.

So 7319 decodes to wind from 230 degrees true at 119 knots - a howling jet stream core.

There’s a natural limit built in. The fastest coded value is 199 knots, and if the direction digits read 77, that’s a special flag meaning the wind is 199 knots or greater. In a piston single you’ll never cruise in that air on purpose - you decode it to know it’s there, and to stay out from under it or use it, depending on your direction.

How Do I Use the Forecast to Pick a Cruise Altitude?

Codes on a page don’t make you a better pilot - decisions do. Here’s the scenario the FB exists to answer.

You’re flying a Cessna 172 from the Midwest, headed roughly west, with a true course near 270 degrees. It’s a nice day, 300 nautical miles, and both 5,500 and 9,500 are legal westbound and clear the terrain. Which do you pick?

Pull the FB for stations along your route, valid for your enroute time. Near 6,000 you see 2730 - wind from 270 true at 30 knots. Near 9,000 it’s stronger, maybe 280 at 40 knots.

Your true course is 270 and the wind is from 270 - that’s a headwind, nearly dead on the nose, and it worsens as you climb. If your 172 trues out around 110 knots and you climb into a 40-knot headwind, your groundspeed drops to 70 knots. That 300-mile trip is now over four hours, and reserves that looked comfortable on the ground become a real question.

Drop to 5,500, take the 30-knot headwind instead, and you buy back 10 knots of groundspeed and a chunk of fuel. Sometimes the lower altitude is the smart altitude - and the only way you’d know is by reading this line.

Now flip it. Tomorrow you fly home eastbound, true course 090. That same wind from 270 is now on your tail. You want to be high, in the strongest wind you can find, because 40 knots of tailwind turns your 110-knot airplane into a 150-knot airplane, and 300 miles goes by in two hours flat.

Same air, same forecast. The wind didn’t change - your direction did. Go low into the wind and high with the wind. The pilot who guesses gets it backwards half the time and never understands why some trips feel so long.

Why Does the Temperature Aloft Matter?

The temperature at your cruise altitude does two jobs.

First, it’s your icing radar. Any time the forecast temperature is at or below 0°C and there’s visible moisture - clouds or precip - you have the ingredients for structural icing. Reading a −8°C at your planned altitude with a front in the area is the forecast tapping you on the shoulder. In a typical trainer with no known-ice certification, that’s a hard look at whether you go, pick an altitude in warmer air, or wait for tomorrow.

Second, it drives your true airspeed and density altitude. Colder air is denser - your engine and wing like it, and your true airspeed for a given indicated changes with it. On your nav log, the temperature aloft is one of the numbers that keeps your groundspeed math honest instead of hopeful.

Where Does the Winds Aloft Fit in a Standard Briefing?

The winds and temperatures aloft is a standard part of every briefing, whether you call Flight Service or pull it up yourself. It comes after the adverse conditions, the synopsis, and the current and forecast conditions.

It’s also the part where most pilots’ eyes glaze over - they’ve already read the METARs and TAFs and feel like they know the weather. Don’t skip it. The METAR tells you what it’s doing at the airport; the winds aloft tells you what the trip in between will feel like. This is the part of the briefing that plans your flight instead of just describing the weather.

Four habits to carry with you:

1. Always match the valid time. Use the forecast that covers when you’ll be up there, not the one current when you woke up.
2. Remember true, not magnetic. Winds aloft are true direction; the tower’s wind is magnetic. Keep them straight or your math will drift.
3. Read more than one altitude. Read the whole column and see what happens 2,000 feet higher or lower. The best altitude is often not the one you assumed.
4. Tie it to terrain and temperature together. The best wind does no good at an altitude that puts you in the ice, below a ridge, or in the bumps. It’s always a blend.

What Does the Examiner Want to See?

The Airman Certification Standards (ACS) expect you to get a standard weather briefing and use it. On your cross-country and checkride, the examiner isn’t looking for you to recite that 9900 means light and variable - that’s a party trick.

They want to see that you took the winds aloft and made a decision with it. That you can point at your nav log and say, “I’m going at 7,500 instead of 9,500 because the headwind was 20 knots less and it kept my reserves legal.” That’s a pilot thinking - and that’s the whole point.

Weather is genuinely hard, and this decoding feels like a foreign language the first few times. But the winds aloft pays you back on every cross-country you ever fly. Ten minutes reading this line can save an hour of flight time and a fuel stop you didn’t plan on. For the full code, the National Weather Service produces the forecast and the FAA’s Aviation Weather Handbook lays out every detail.

Key Takeaways

• The winds and temperatures aloft (FB) forecast is a National Weather Service model prediction of wind direction, speed, and temperature at standard altitudes - a forecast, not an observation, so match the valid time to your enroute time.
• Decode each group as direction (true) + speed (knots) + temperature (°C); e.g., 2426+03 = wind from 240° true at 26 knots, +3°C. Above 24,000 feet, an unsigned temperature is always negative.
• 9900 means light and variable (under 5 knots). For winds 100 knots or more, subtract 50 from the direction and add 100 to the speed - so 7319 = 230° true at 119 knots.
• Fly low into a headwind and high with a tailwind; the right altitude can swing your groundspeed by tens of knots and hours of flight time.
• Use the temperature aloft as an icing check (at or below 0°C with visible moisture) and to keep your true airspeed math honest.