The Winds Aloft Forecast, Decoding a Line of the FB Product, and How Two-Six-Three-Five-Minus-Oh-Eight Tells You Which Altitude to Actually Fly

The winds and temperatures aloft forecast - now called the FB product (formerly FD) - is a National Weather Service forecast that tells you the expected wind direction, wind speed, and temperature at a stack of specific altitudes over your route. A coded group like 2635-08 means the wind is forecast from 260 degrees true at 35 knots, with a temperature of -8°C at that altitude. Reading it correctly lets you “shop” for the cruise altitude that costs you the least headwind - turning a fuel-sweat cross-country back into the flight you actually planned.

What Is the Winds Aloft Forecast and Where Does It Come From?

Every other product in your weather briefing tells you whether you can go. The winds aloft forecast tells you how to go. It’s the product that decides whether your three-hour cross-country stays three hours or stretches into a four-hour fuel emergency.

The FB product comes from the National Weather Service, specifically the Aviation Weather Center in Kansas City. Critically, it is a forecast, not an observation - someone ran the models and predicted what the wind and temperature will be doing at specific altitudes, at a specific valid time, over a specific set of reporting points.

Because it’s a forecast, it has a valid time. There are three issuances a day, each valid for a different window. If you pull it up at 6 a.m. for a 2 p.m. departure, make sure you’re reading the issuance that actually covers 2 p.m. Grab the wrong one and you’ve done careful math on the wrong sky.

What Altitudes Does the FB Forecast Cover?

The forecast is built in columns, and each column is an altitude in feet. The standard stack is 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 feet.

If you fly a piston single, you live in the first handful - 3,000, 6,000, 9,000, and 12,000. That’s your neighborhood.

Two rules about these altitudes trip up almost everyone:

• No wind is forecast within 1,500 feet of the station’s elevation. A reporting point sitting at 5,000 feet in the mountains won’t show a 3,000-foot line - that altitude is underground. The column is simply blank.
• No temperature is forecast within 2,500 feet of the station. So the lowest altitude in a station’s block often shows a wind with no temperature attached. That’s not an error - it’s the rule doing its job.

How Do You Decode a Winds Aloft Group Like 2635-08?

A full group is six characters and a sign: 2635-08. Break it into three pieces.

First two digits - wind direction. “26” is in tens of degrees, so it means 260 degrees. Here’s the detail that wrecks navigation math: this direction is referenced to true north, not magnetic. Every runway number, every heading the tower gives you, is magnetic - but the winds aloft forecast is true. Before you use it against a magnetic course, apply your local magnetic variation. In some regions that’s a rounding error; in others it’s 10, 12, or 15 degrees. That’s real.

Next two digits - wind speed in knots. “35” means 35 knots.

Last portion - temperature in Celsius. “-08” means -8°C at that altitude.

Put it together: 2635-08 = wind from 260° true at 35 knots, temperature -8°C. Direction, speed, temperature. Once you see the seams, you can’t unsee them.

What Are the Three Special Cases in the FB Product?

The FB product hides three landmines. Learn them before you step on them.

1. Light and variable - coded 9900. When the wind is expected to be less than 5 knots, they don’t assign a direction. They code it 9900. Don’t hunt for a “990-degree” wind - there’s no such thing. 9900 simply means light and variable, nothing worth correcting for.

2. Strong winds - the “add 50, subtract 100” trick. Direction never exceeds 360 degrees, so the direction digits should never be higher than “36.” When wind speed is between 100 and 199 knots, the coders add 50 to the direction and subtract 100 from the speed.

Example: you see 7319. Your instinct says “730 degrees at 19 knots” - which is impossible, and that impossibility is the clue. When the first two digits exceed 36, the trick is in play. Subtract 50 from the direction (73 − 50 = 23 → 230 degrees) and add 100 to the speed (19 + 100 = 119 knots). So 7319 = wind from 230° true at 119 knots - a jet stream wind you’ll meet in the flight levels.

3. Missing minus signs up high. Above 24,000 feet, the air is essentially always below zero, so they drop the minus sign to save space. A temperature with no sign at 30,000 feet is negative - assume the cold. Down low, where it could go either way, they always print the sign.

How Do You Use the Forecast to Pick an Altitude?

Codes are just codes until they change a decision. Here’s the scenario.

You’re planning a cross-country with a true course of roughly due west, 270 degrees. Your trainer trues out around 110 knots. You’re deciding between 6,000 and 9,000 feet for the westbound leg.

You pull the FB product near your midpoint:

• At 6,000 feet: wind from 240° at 15 knots.
• At 9,000 feet: wind from 260° at 35 knots.

You’re heading west, into the wind either way. At 6,000, a 15-knot near-headwind costs you roughly a dozen knots of groundspeed. At 9,000, the 35-knot near-headwind costs you 30 knots or more. Same airplane, same route, same fuel - but the 9,000-foot leg could take a half hour longer and eat into your reserve.

The forecast isn’t there to be decoded for its own sake. It’s there so you can shop for an altitude. Going west into a headwind? Get low, find the weaker wind, respect the terrain, airspace, and oxygen rules, and pick the level that costs you least. Coming back east that afternoon? That same headwind becomes a tailwind - going higher, where it’s stronger, might hand you a free 30 knots. Use the wind both ways.

Why Does the Temperature Half of the Group Matter?

That “-8” isn’t decoration. It feeds two things you care about.

True airspeed. Temperature at a given pressure altitude changes what your airspeed indicator is really telling you - exactly the input your E6B or electronic flight bag needs to compute your flight plan.

The freezing level - the safety one. If the temperature crosses through zero somewhere between 6,000 and 9,000 feet and there’s visible moisture forecast, you’ve just found the altitude band where structural icing lives. In a non-known-ice airplane, that’s not a shopping decision - it’s a stay-out-of-there decision.

How Will This Come Up on Your Checkride?

Under the Airman Certification Standards (ACS), the examiner will have you pull a real weather briefing for a proposed cross-country. They’re allowed to point at a block of winds aloft code and say, “Decode this. What are the winds at 9,000? What’s the temperature?”

They’re looking for two things. First, that you can read the group - direction, speed, sign - without fumbling. Second, and this is what separates a pass from a strong exam, that you connect it to a decision. Don’t just say “that’s 260 at 35.” Say: “That’s a 35-knot near-headwind at 9,000, so I’d look lower - and the freezing level’s right about here, so with that layer forecast I’m staying below it.” That shows you fly the weather instead of reciting it.

How Do You Actually Get Good at This?

None of this is easy when you’re new. It’s a stack of little rules - true versus magnetic, the add-50/subtract-100 trick, the missing minus signs - and nobody reads their first forecast and just gets it.

You get it by decoding one, out loud, before every flight, until one day you glance at 7319 and your brain says “230 at 119” without asking permission.

Here’s the homework. Before your next flight - cross-country or just the practice area - pull the winds and temperatures aloft forecast for your area. Pick the two altitudes closest to where you actually fly. Decode them out loud: direction, speed, temperature. Then ask the only question that matters: given where I’m going, does this wind help me or hurt me, and is there a better altitude sitting right there in the numbers? Do that ten times and it’s yours forever.

Key Takeaways

• The FB product (formerly FD) is a National Weather Service forecast of wind and temperature at set altitudes - it’s a forecast with a valid time, so use the right issuance.
• Decode each group as direction (true north) + speed (knots) + temperature (°C): 2635-08 = 260° true, 35 knots, -8°C.
• Watch the three special cases: 9900 = light and variable; direction digits over 36 mean subtract 50 / add 100 (e.g., 7319 = 230° at 119 kt); above 24,000 ft the missing minus sign is still negative.
• Convert the true wind direction to magnetic using local variation before computing wind correction angle.
• Use the forecast to shop for the best altitude - lower into a headwind, higher for a tailwind - and use the temperature to spot the freezing level and structural icing risk.