The Winds and Temperatures Aloft Forecast, the Coded Table That Tells You Which Altitude to Fly and Whether You're About to Pick Up Ice

The Winds and Temperatures Aloft forecast (product identifier FB, formerly called the FD or “winds aloft”) is a computer-generated National Weather Service product that predicts wind direction, wind speed, and air temperature at multiple altitudes over specific forecast points. Reading it lets you choose the cruising altitude with the best tailwind and spot the cold layers where structural icing becomes a real threat. Once you learn the coded format, that grid of four- and six-digit numbers becomes one of the most valuable tools in your entire weather briefing.

What Is the Winds and Temperatures Aloft Forecast?

The FB is a forecast delivered through your standard briefing sources that predicts three things at a stack of altitudes: wind direction, wind speed, and air temperature. It covers a list of specific forecast points around the country, each identified by a three-letter code.

You’ll see the letters FB in front of it - that’s just the product identifier. Many experienced pilots still call it the “winds aloft” or the FD, which was the old identifier before the format was modernized. The concept is the same: wind and temperature, layer by layer, going up.

Why the Winds Aloft Forecast Matters

There are two big reasons to care about this product, and neither is trivia.

Time and fuel. The winds at 3,000 feet and the winds at 9,000 feet can be completely different in both direction and speed. Pick the right altitude and you can gain a 20, 30, or 40 knot tailwind. Pick the wrong one and you crawl home into a headwind, watching your fuel and your patience run down. On a cross country, no single decision affects your ground speed more than altitude selection.

Icing. The temperature column tells you how cold it is aloft. Cold air plus visible moisture equals structural icing. If you fly an airplane with no ice protection - and most of us do - that temperature number is a genuine safety-of-flight item.

How Do I Read the Winds Aloft Table?

The forecast is laid out like a table. Down the left side is a list of station identifiers - three-letter codes for forecast points like Chicago, Denver, and St. Louis. Find the one closest to your route, or better yet, look at a couple that bracket where you’ll actually be flying.

Across the top is a row of altitudes: 3,000, 6,000, 9,000, 12,000, 18,000 feet, and higher. Here’s the first thing that trips people up - these altitudes are all in feet above mean sea level (MSL), not above the ground. That’s the same reference as your altimeter set to local pressure. So the 9,000-foot column is the wind at 9,000 feet on your altimeter, not 9,000 feet above the terrain.

How Do I Decode the Wind and Temperature Numbers?

Take a basic group like 2420+05. Read it as “two-four, two-zero, plus-zero-five.” It breaks into three parts:

• First two digits - wind direction. “24” means 240 degrees. Critically, this is degrees true, not magnetic. The entire weather system works in true north, while your heading indicator works in magnetic, so you must account for magnetic variation before using this wind in the cockpit.
• Next two digits - wind speed in knots. “20” means 20 knots.
• Final digits - temperature in degrees Celsius. “+05” means plus 5°C.

Put together, 2420+05 means the wind is from 240 degrees true at 20 knots, and the temperature at that altitude is +5°C. That’s the whole language: direction, speed, temperature.

What Are the Coding Tricks I Need to Know?

There are two coding tricks that examiners look for you to understand.

Trick 1 - Negative temperatures above 24,000 feet. Above the 24,000-foot level, every temperature is negative, so the sign is dropped to save space. A high-altitude group ending in “42” with no sign means minus 42°C - you assume the minus. Below 24,000 feet, the plus or minus is always spelled out, because down low the temperature could go either way.

Trick 2 - Winds of 100 knots or more. Wind direction only goes up to 36 (for 360 degrees), and speed only has two digits. When the wind is 100 knots or more, the coders add 50 to the direction and subtract 100 from the speed. So a coded direction of “73” - impossible on its own, since there’s no 730 degrees - is your flag: subtract 50 to get a direction of 230 degrees, then add 100 back to the speed. A coded speed of “05” with that flag actually means 105 knots.

The rule of thumb: watch for a direction number bigger than 36. The moment you see one, decode it as a 100-knot-plus wind.

Special case - light and variable. If you see the group 9900, that’s the code for light and variable: wind less than 5 knots with no particular direction.

Why Are Some Boxes Blank?

The forecast has deliberate blank spots, and they aren’t errors.

The FB won’t give you a wind for any altitude within about 1,500 feet of the station’s elevation. For a high station out west, you won’t see a 3,000-foot or even a 6,000-foot forecast, because the ground is already up around there.

It also won’t give a temperature for any level within about 2,500 feet of the station. A blank box is simply telling you that level is too close to the surface to forecast reliably. Read the levels that are actually there.

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

Say you’re planning a cross country of a few hundred miles, generally headed east. Legally, on an eastbound magnetic course VFR above 3,000 feet AGL, you’d fly odd thousands plus 500: 5,500, 7,500, 9,500, and so on.

You pull the winds aloft for a station near your route:

• At 6,000 feet: wind from 260 degrees at 15 knots.
• At 9,000 feet: wind from 250 degrees at 35 knots.

Flying east, a wind from the west is a tailwind. Down at 6,000 you get a 15-knot push; up at 9,000 you get a 35-knot push. That’s a 20-knot difference in free ground speed for climbing just 3,000 feet higher - real minutes and real gallons on a long leg.

But don’t automatically go high. Climbing costs time and fuel to get up there, may put you closer to a cloud layer, shortens your glide options if the engine quits, and - high enough - brings in supplemental oxygen requirements and simple fatigue. You weigh the tailwind against all of that. The point is that you’re now deciding with real numbers instead of guessing.

Now flip the trip. Coming home westbound into that same wind, the high altitude punishes you: 35 knots on the nose at 9,000 versus 15 knots on the nose at 6,000. Going home, you might deliberately fly lower to duck under the worst of it. Same trip, opposite direction, opposite answer.

Should I Read More Than My Planned Altitude?

Yes - read the whole column, not just the altitude you planned to fly. Read 3,000, 6,000, 9,000, and 12,000 to get a picture of how the wind changes as you climb.

Sometimes the story isn’t the speed; it’s the shear. If the wind swings hard in direction or jumps sharply in speed over just a few thousand feet, that’s a heads-up for a rough ride and a clue about what the atmosphere is doing.

How Does the Temperature Column Warn Me About Ice?

Suppose 9,000 feet reads minus 02 - two degrees below freezing - and the rest of your briefing (ceilings, AIRMETs, the big picture) tells you there’s moisture up there. Cold air plus visible moisture is the recipe for structural icing. In a typical light airplane with no known-ice protection, that combination is a stop sign, not a maybe. The winds aloft temperature is often the first place you’ll catch it, because it puts an actual number on how cold each layer is.

You can also use the temperature column to find the freezing level - the altitude where the number crosses from plus to minus. Below that line the air is above freezing; above it, below. On a cool, damp day, staying below the freezing level, where the air is too warm to freeze on you, is often your out.

As a bonus, a cool, moist layer in that table is one more clue that conditions are ripe for carburetor ice, which doesn’t require freezing temperatures at all. The FB won’t hand you a carb ice warning, but it’s a reason to keep your hand near the carb heat knob.

Key Takeaways

• Don’t scroll past the winds aloft. Find the two or three forecast points nearest your route and read them every time.
• Direction is true and altitudes are MSL. Convert for magnetic variation before using the wind, and read altitudes off your altimeter, not the terrain.
• Read the whole altitude column to let the winds pick your altitude going out and coming home - free ground speed is free ground speed.
• Watch for a direction bigger than 36, your 100-knot-plus flag (subtract 50, add 100), and remember 9900 means light and variable.
• Use the temperature column to find the freezing level; cold plus moisture means think hard before you launch.