The Winds Aloft Forecast, the Four-Digit Code Every Cross-Country Student Has to Crack, and the Altitude Decision You Cannot Make Without It

The Winds Aloft forecast - officially called the FB winds forecast, or Forecast Winds and Temperatures Aloft - is one of the most actionable tools in your pre-flight weather brief. It tells you the wind direction, wind speed, and temperature at multiple altitude levels along your route, giving you the data to choose a cruise altitude that works in your favor. Skipping it, or treating it as a footnote, is a common mistake that costs pilots groundspeed, fuel, and margin.

What Is the Winds Aloft Forecast and Where Do You Find It?

The Winds Aloft forecast was previously called the FD forecast but was renamed the FB forecast several years ago. The underlying data is the same - the label changed. You’ll find it on the Aviation Weather Center website at aviationweather.gov, or your briefer will include it during a standard weather briefing.

The forecast is issued four times daily and covers either a 12-hour or 24-hour outlook. When planning a flight, use the forecast period that actually covers your departure and en-route time. An expired forecast period is not useful.

Why Does the Winds Aloft Forecast Matter for Cross-Country Flights?

Three reasons make this forecast essential rather than optional.

First, it shows you which altitude works best for your direction of travel. A 30-knot headwind at 6,000 feet might drop to 12 knots at 3,000 feet. That difference directly changes your groundspeed math, your fuel stop calculations, and how much reserve you land with.

Second, the temperature data at altitude tells you about icing risk. If the forecast shows temperatures below 0°C at your planned cruise altitude and there’s moisture in the area, you need to know that before departure. Carburetor ice risk in carbureted engines is also a function of temperature and humidity at altitude.

Third, accurate temperature data sharpens your true airspeed calculations. Better true airspeed feeds into more accurate fuel burn estimates and a tighter time-en-route figure. Without it, you’re working with rough approximations.

How Do You Decode the Four-Digit Winds Aloft Code?

Each altitude entry in the Winds Aloft table is a four-digit group, often followed by a temperature in degrees Celsius. Here’s how to read it.

Take the entry 1825:

• First two digits (18): Wind direction. Multiply by 10. 18 × 10 = 180°. The wind is from due south.
• Second two digits (25): Wind speed in knots. 25 knots.

If a temperature follows - say, minus 10 - that’s degrees Celsius at that altitude level.

So 1825 / −10 means: winds from 180° at 25 knots, temperature −10°C.

That’s the complete decode for the vast majority of entries you’ll encounter.

What Are the Special Cases in the Winds Aloft Format?

A few exceptions appear regularly enough that you need to know them before your checkride.

9900 means calm or light and variable winds. You’ll see it on quiet days at lower altitudes.

The 3,000-foot level does not include temperature data. Surface-level temperatures are covered elsewhere in the weather brief.

When wind speeds exceed 100 knots, a special encoding is used. Forecasters add 50 to the direction code and subtract 100 from the speed. If you see a direction code greater than 50, that’s your flag. For example, an entry of 7345 breaks down as: 73 is greater than 50, so subtract 50 → 23, meaning 230°. Add 100 to 45 → 145 knots. This encoding won’t appear often at typical light aircraft altitudes, but it’s a common checkride question.

Does Wind Direction in the Forecast Use True or Magnetic Heading?

The Winds Aloft forecast gives true direction, not magnetic. This matters most in areas with significant magnetic variation - particularly in the western United States. When comparing a forecast wind direction to your compass heading, account for local magnetic variation. Your sectional chart shows the variation values for your area.

How Do You Use the Winds Aloft Forecast to Select a Cruise Altitude?

The most practical application is altitude selection before a cross-country. For each altitude level available at stations along your route, estimate what the wind is doing to your groundspeed.

You don’t need precise vector math for initial planning. A useful rule of thumb: if the wind direction is within about 30° of your heading, treat it as a headwind or tailwind component. Beyond that, it’s primarily a crosswind and contributes less to your groundspeed either way.

After estimating groundspeed at each altitude, factor in temperature. Are freezing temperatures near a cloud layer ruling out certain levels? Does terrain along the route set a floor on your altitude options? Is your aircraft’s service ceiling or oxygen requirements relevant? The Winds Aloft forces you to work through all of it before settling on a cruise altitude.

What Does a Real Altitude Decision Look Like?

Eastbound example: You’re flying a heading of 090° (due east). At 6,000 feet, the Winds Aloft shows 270° at 30 knots - almost directly on the nose. If your true airspeed is 115 knots, your groundspeed drops to roughly 85 knots. At 9,000 feet, the forecast shows 240° at 12 knots - a quartering tailwind. Groundspeed climbs to around 120 knots. That’s 35 knots recovered by climbing 3,000 feet higher.

Westbound example (Kansas City to Denver): On a westbound route, you’re almost certainly flying into some headwind. Suppose the Winds Aloft shows:

• 6,000 ft: 270° / 25 knots / −5°C
• 9,000 ft: 280° / 35 knots / −12°C
• 12,000 ft: 290° / 45 knots / −19°C

The headwind worsens as you climb, so lower looks better for groundspeed. But the temperatures at 6,000 and 9,000 feet are both below 0°C. Near any moisture, those levels are in the structural icing window. And Denver sits at approximately 5,300 feet elevation, so terrain - especially as you approach the Front Range - is pushing your minimum safe altitude upward regardless of wind preference.

This is the tradeoff the Winds Aloft is designed to surface. Groundspeed, icing, terrain, performance ceiling, and ATC considerations all get weighed before you finalize a cruise altitude.

What Do Checkride Examiners Expect About Altitude Selection?

The Airman Certification Standards are specific on this point. At your private or instrument checkride, the examiner won’t just ask what altitude you filed. They’ll ask why.

“The Winds Aloft showed the most favorable groundspeed at 6,000 feet, and the temperatures were above 0°C, so structural icing was not a concern at that level” is the kind of answer that shows you used the forecast as a decision tool - not that you picked a number and moved on. If you can’t explain your altitude choice in terms of the weather data, that’s a gap the ACS expects you to close.

What Mistakes Do Students Make With the Winds Aloft Forecast?

Looking at only one altitude at one station. Pull data for multiple altitude levels and multiple stations along your route. Do the winds tell a consistent story? If one station looks dramatically different from its neighbors, that’s worth a closer look before you commit to a cruise altitude.

Not verifying forecast validity. Know the issue time and the valid period. Outdated data is not a weather brief.

Ignoring missing altitude levels. Some stations - particularly those at higher elevations - won’t show data for lower altitude levels. This happens when a forecast altitude is within 2,500 feet of the ground elevation at that station. If your target cruise altitude is blank, move up to the next available level.

How Should You Build Your Skills With the Winds Aloft Forecast?

Before every cross-country, pull the Winds Aloft table and write down the winds and temperatures for at least three altitude levels at each major station along your route. Calculate a rough groundspeed at each level. Pick the altitude that makes sense across wind, icing, terrain, and performance. Then, once airborne, note your actual groundspeed and compare it to your estimate.

Were you close? Were you off? If so, why - did the winds shift, or did you not account for altitude variation along the route? Do this on every cross-country and you’ll build calibrated intuition that no ground school can replicate.

What’s the Full Step-by-Step Winds Aloft Planning Process?

Step 1. Pull the Winds Aloft forecast from aviationweather.gov or request it from your briefer. Confirm the valid time covers your planned flight.

Step 2. Identify the stations along your route that are representative of the air mass you’ll fly through.

Step 3. Decode the four-digit entries: first two digits × 10 = true wind direction; second two digits = wind speed in knots. Watch for the high-speed encoding (direction code > 50). Note temperatures.

Step 4. Estimate the headwind or tailwind component at each altitude level. No complex math - just a sense of whether the wind is helping or hurting your groundspeed.

Step 5. Check temperatures for icing risk. Does a cloud layer at freezing or sub-freezing temperatures constrain your options?

Step 6. Pick your altitude. Balance favorable winds, icing clearance, terrain clearance, aircraft performance, and any ATC requirements.

Step 7. Once airborne, compare your forecast groundspeed to actual. Adjust your fuel math and time en route if needed.

Key Takeaways

• The FB winds forecast (formerly FD) gives wind direction, wind speed in knots, and temperature in °C at altitudes from 3,000 to 39,000 feet - valid for either a 12- or 24-hour period, issued four times daily.
• Decode four-digit entries by multiplying the first two digits by 10 for true direction and reading the second two digits as speed in knots. The entry 9900 means calm or light and variable.
• When wind speed exceeds 100 knots, the direction code exceeds 50 - subtract 50 for true direction, add 100 to the speed value.
• Winds aloft directions are true, not magnetic. Adjust for local variation when comparing to your compass heading.
• Altitude selection is a multi-variable decision: groundspeed, icing risk, terrain, performance, and ATC requirements all factor in - and your examiner will ask you to explain your reasoning in those terms.