Winds aloft forecasts use a compact code of numbers that, once you understand the pattern, take only seconds to read. The forecast (called an FB report) lists wind direction, wind speed, and temperature at various altitudes for stations across the country. Each altitude gets a short block of digits, and the trick is knowing how to split those digits apart.
How the Report Is Organized
An FB report lists station identifiers down the left side and altitude columns across the top. The standard altitudes are 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 feet MSL. Not every station gets every altitude. The first reported level must be at least 1,500 feet above the station’s elevation, so a station sitting at 5,000 feet won’t have a 3,000 or 6,000 foot entry.
Temperature is included at all levels that are 2,500 feet or more above the station. The 3,000-foot level never includes a temperature forecast, regardless of station elevation. At 30,000 feet and above, temperatures are always negative, so the minus sign is dropped to save space.
The National Weather Service updates these forecasts daily, based on the 1200 UTC model run, with data typically available by 1400 UTC.
Breaking Down a 4-Digit Wind Group
At the 3,000-foot level, you’ll see a four-digit code like 2426. The first two digits are the wind direction in tens of degrees (true north), and the last two are the speed in knots. So 2426 means the wind is from 240 degrees at 26 knots.
Direction is always rounded to the nearest 10 degrees. A code starting with 27 means 270 degrees (due west). A code starting with 36 means 360 degrees (due north).
Breaking Down a 6-Digit Group
At 6,000 feet and above, where temperature is included, the code expands to six digits. For example, 270926 breaks down like this:
- 27: wind direction, 270 degrees
- 09: wind speed, 9 knots
- 26: temperature, but you need context to know positive or negative
Wait, that example needs a closer look. The group 2726-09 would actually appear as 272609. The first two digits (27) give direction, the next two (26) give speed, and the last two (09) give temperature. So that’s 270 degrees at 26 knots, temperature minus 9°C. At lower altitudes the sign (plus or minus) is shown explicitly. At 30,000 feet and above, every temperature is assumed negative, so no sign appears.
Winds Over 100 Knots
The code only has two digits for direction and two for speed, which creates a problem when wind speed exceeds 99 knots. The solution: add 50 to the direction code and subtract 100 from the speed. If you see a direction value between 51 and 86, that’s your signal.
For example, a group starting with 7545 means the direction is 75 minus 50, giving 250 degrees. The speed is 45 plus 100, giving 145 knots. Whenever the first two digits are above 36 (since 360 degrees is the maximum real direction), you know the 50/100 rule is in play.
Light and Variable Winds
When forecast winds are below 5 knots, the direction and speed digits are coded as 9900. This means “light and variable,” meaning the wind is too weak and inconsistent to assign a meaningful direction. If you see 9900 followed by a temperature, read it as calm or near-calm wind at that altitude. For instance, 990000 means light and variable winds with a temperature of zero degrees Celsius.
A Complete Example
Suppose you pull up the FB report for a station and see this row:
3,000: 2426 6,000: 2726-09 9,000: 2830-18
Here’s what you’re looking at:
- 3,000 ft: Wind from 240° at 26 knots, no temperature reported
- 6,000 ft: Wind from 270° at 26 knots, temperature -9°C
- 9,000 ft: Wind from 280° at 30 knots, temperature -18°C
Notice the wind backing slightly and picking up with altitude. That kind of pattern is exactly what you’re looking for during flight planning.
Using Winds Aloft for Flight Planning
The whole point of reading these forecasts is figuring out your groundspeed, which drives your time enroute and fuel burn. Your true airspeed stays constant for a given power setting and altitude, but wind pushes you faster or slower over the ground depending on whether it’s a tailwind, headwind, or crosswind.
To calculate groundspeed, you need three pieces: your true airspeed, the wind direction, and the wind speed. You can work this out with an E6B flight computer, an electronic flight calculator, or flight planning software. The process involves finding the angle between your course and the wind direction, then computing the headwind or tailwind component.
An NTSB fuel planning worksheet from an actual accident investigation illustrates how this works in practice. For a flight leg of 157 nautical miles at 110 knots true airspeed with winds from 240° at 8 knots, the estimated flight time was 80 minutes, requiring about 16 gallons of fuel. Change the wind, and both numbers shift. On a shorter 14-mile leg with calm winds, the same airplane needed only 8 minutes and 2 gallons. Small differences in wind speed compound over long legs, making accurate winds aloft data critical for fuel planning on cross-country flights.
Choosing the Right Altitude
Since the report gives you winds at multiple altitudes, you can compare them to pick the most favorable cruising altitude. A 20-knot headwind at 6,000 feet might become a 10-knot headwind at 9,000 feet, saving you real time and fuel. On the other hand, climbing higher burns more fuel getting there, so the tradeoff isn’t always obvious for short trips.
If your planned altitude falls between two reported levels, interpolate. Flying at 7,500 feet? Split the difference between the 6,000 and 9,000 foot data. The forecast won’t be exact at any specific altitude anyway, so a rough interpolation is perfectly adequate for planning purposes. Winds aloft are forecasts, not observations, and actual conditions will vary. But they’re the best planning tool available, and reading them correctly is a fundamental skill for any pilot flying cross-country.