The winds and temperatures aloft forecast and the six-digit code that tells you what is waiting at your cruise altitude

The winds and temperatures aloft forecast (FD) is a six-digit code that tells you the wind direction, wind speed, and temperature at your planned cruise altitude. Decoding it takes seconds once you know the pattern, and using it properly can save significant fuel and time on every cross-country flight.

What Is the Winds and Temperatures Aloft Forecast?

The FD forecast — sometimes called the “winds aloft” — is issued twice daily at 0000Z and 1200Z. It provides wind and temperature data at standard altitudes: 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 feet. Forecasts are available for 6-, 12-, and 24-hour periods, with extended forecasts out to 48 hours.

You’ll find it as part of any standard weather briefing, whether through Flight Service or 1800wxbrief.gov. The report is formatted as a table with reporting stations (airport identifiers like DCA, JFK, ORD) down the left side and altitudes across the top.

How Do You Decode the Six-Digit Wind Group?

Each entry in the table is a group of digits. The most common format is six digits plus a temperature. Here’s how to read them:

• First two digits: Wind direction in tens of degrees
• Next two digits: Wind speed in knots
• Last two digits (with +/-): Temperature in degrees Celsius

Example: 2704506. The wind direction is 270 degrees (west). The speed is 45 knots. The temperature is +06°C.

At and below 24,000 feet, temperatures include a plus or minus sign. Above 24,000 feet, temperatures are always negative, so the sign is dropped.

What Does 9900 Mean in the Winds Aloft?

When wind speed is less than 5 knots, the group is coded as 9900 — four nines followed by two zeros. This means the wind is light and variable. Direction is irrelevant because there’s essentially no wind.

This is a common checkride question. If you see 9900, just say “light and variable.”

How Are Winds Over 100 Knots Encoded?

When wind speed exceeds 100 knots, the code uses a mathematical trick because three-digit speeds won’t fit in a two-digit space:

1. Add 50 to the wind direction
2. Subtract 100 from the wind speed

Example: Wind from 270° at 130 knots becomes 7730. The direction 27 + 50 = 77. The speed 130 − 100 = 30.

To decode: If the first two digits are greater than 36, subtract 50 from the direction and add 100 to the speed. So 7730 becomes 270° at 130 knots.

This typically appears only at 18,000 feet and above, but examiners expect you to understand the method.

Practice Examples

Why Do the Winds Aloft Matter for Cross-Country Planning?

Your groundspeed — and therefore your fuel burn and time en route — depends entirely on the wind at your cruise altitude. The numbers add up fast.

A Cessna 172 cruising at 110 knots TAS with a 20-knot headwind has a groundspeed of only 90 knots. On a 200-nautical-mile trip, that’s roughly 2 hours 13 minutes instead of 1 hour 49 minutes — an extra 24 minutes of fuel burn you didn’t plan for. A 20-knot tailwind does the opposite, cutting the trip to about 1 hour 32 minutes.

This is why smart pilots check winds at two or three altitudes and pick the one with the most favorable wind. A brutal headwind at 6,500 feet might become a helpful tailwind at 8,500 feet. The FD forecast is the tool that reveals this.

How Do You Interpolate Between Reported Altitudes?

The forecast reports standard altitudes (3,000, 6,000, 9,000, etc.), but you’ll often cruise between them. If you’re flying at 5,500 feet, look at both the 3,000- and 6,000-foot reports and estimate the midpoint.

If the wind at 3,000 is from the west at 10 knots and at 6,000 it’s from the west at 20 knots, figure roughly 15 knots at your altitude. Precision isn’t necessary for VFR planning — a reasonable estimate works.

Important: No winds aloft data is issued for altitudes within 1,500 feet of station elevation. A station like Denver at 5,300 feet MSL won’t have data for 3,000 or 6,000 feet — the report starts at 9,000. This catches many pilots off guard when planning flights through the western states.

How Do the Winds Aloft Fit Into Your Weather Briefing?

The FD forecast fills a gap that surface observations can’t cover. A METAR tells you conditions on the ground right now. A TAF forecasts conditions at the airport. The winds aloft tell you what’s happening between airports, at altitude — where you’re actually flying.

You can have clear skies at both departure and destination while facing a 40-knot headwind with turbulence at cruise altitude. Surface observations won’t warn you. The winds aloft will.

Can the Winds Aloft Predict Turbulence?

A large change in wind speed or direction between adjacent altitudes indicates wind shear, which typically means turbulence. If the wind at 6,000 is from the southwest at 15 knots and at 9,000 it’s from the northwest at 40 knots, expect rough air in that transition zone.

Spotting this before departure lets you brief passengers, secure the cabin, and potentially choose a smoother altitude.

What Does the ACS Require You to Know?

The Airman Certification Standards for the private pilot certificate require you to obtain, read, and analyze the winds and temperatures aloft forecast. On the oral exam, expect the examiner to:

• Hand you an FD report and ask you to decode it
• Ask what 9900 means
• Ask how to decode direction values above 36
• Ask how you’d use this data to plan a cross-country

A Practical Habit for Your Next Flight

On your next cross-country, check the winds aloft at three altitudes that make sense for your route. Pick the altitude with the most favorable wind. Calculate your groundspeed using that wind and compare it to what your flight planning app shows. If there’s a significant difference, figure out why before you fly.

Key Takeaways

• The six-digit code breaks down as: two digits for direction (in tens of degrees), two for speed (knots), and two for temperature (°C)
• 9900 means light and variable — wind speed under 5 knots
• Direction above 36 means 50 was added to direction and 100 subtracted from speed — reverse the math to decode
• Check multiple altitudes before committing to a cruise altitude; the best groundspeed might be a couple thousand feet higher or lower
• No data is reported for altitudes within 1,500 feet of station elevation