The Winds Aloft Forecast - Decoding the FD Winds and Finding the Altitude That Works in Your Favor

The Winds and Temperatures Aloft Forecast - called the FB winds or FD winds interchangeably - is one of the most valuable products in a preflight briefing and one of the most misread. Students learn it exists, learn how to find it, but rarely learn how to decode a full table and use it to make a real altitude decision. That’s the gap this article closes.

What Is the Winds and Temperatures Aloft Forecast?

The forecast is issued four times daily by the National Weather Service at 0000, 0600, 1200, and 1800 Zulu. Each issuance includes three forecast time horizons: 6-hour, 12-hour, and 24-hour. Select the one whose valid time overlaps with your actual en route window.

This matters more than it sounds. Pulling up the 6-hour product without confirming it’s still valid during your flight is a common mistake. If you’re flying in the afternoon and the 6-hour product expired at noon, you need the 12-hour forecast. Match the valid time to your en route window.

You can find the full product on the Aviation Weather Center at aviationweather.gov, or embedded in your electronic flight bag. ForeFlight, FlyQ, and Garmin Pilot all pull and display this data in a table format that’s easier to read than raw text.

How Is the Forecast Organized?

Data is organized by reporting station - three-letter identifiers, usually VORs or major reporting locations - across standard altitude levels: 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 feet MSL. General aviation piston cross-countries are mostly planned in the 3,000–12,000 foot range.

Two hard limits apply before reading any numbers. First, no forecast data exists within 1,500 feet of a reporting station’s elevation - a station sitting at 4,500 feet will have no 3,000-foot entry. Second, the 3,000-foot level carries no temperature data. Temperature information starts at 6,000 feet.

Are Winds Aloft Directions True or Magnetic?

True degrees. This is the single most important caveat in the entire product. Your compass, directional gyro, and instrument approaches all use magnetic. When manually calculating a wind correction angle from forecast data, you must apply magnetic variation for your area. Your EFB typically handles this automatically - but on a checkride oral, the examiner will ask whether you understand the difference. Winds aloft: true. Navigation: magnetic.

How Do I Decode a Winds Aloft Entry?

The encoding format is DDSSTT: direction, speed, temperature. Break every entry into those three pieces.

Using the example 2318−04:

• DD → 23: multiply by 10 → 230° true (wind from the southwest)
• SS → 18: 18 knots
• TT → −04: −4°C

At whatever altitude that entry covers, the wind is from 230° true at 18 knots with an air temperature of −4°C.

What Do the Special Codes Mean?

9900 - light and variable winds. When the direction field reads 99 and the speed field reads 00, forecast winds are less than 5 knots with no meaningful direction. This is exactly what it looks like on a good cross-country day.

Winds over 100 knots - jet stream encoding. When winds exceed 100 knots, the system encodes by adding 50 to the direction code and subtracting 100 from the speed. Any direction code of 51 or higher is the signal.

Example: 731960 at a high-altitude level.

• Direction code 73: ≥51, so subtract 50 → 23 × 10 = 230° true
• Speed 19: add 100 → 119 knots
• Temperature: −60°C

General aviation cruising altitudes won’t see these speeds. They appear regularly on checkride weather scenario questions - the examiner hands you a table with a 70-something direction code and watches what you do with it.

Temperature above FL240. Above 24,000 feet MSL, temperatures are always negative, so the minus sign is omitted to save space. A temperature field reading 40 at 30,000 feet means −40°C. Below FL240, the sign is always explicit.

Why Does the Temperature Column Matter Beyond Comfort?

The forecast temperature at altitude feeds directly into three flight planning factors.

Density altitude. Air significantly warmer than standard degrades aircraft performance. Fifteen degrees above ISA at 9,000 feet will show up in your climb rate and true airspeed.

Icing potential. The temperature column tells instrument pilots - and any VFR pilot flying near visible moisture - where the freezing level sits in the forecast. Any altitude near 0°C with visible moisture in the area requires a serious icing assessment before departure.

True airspeed calculation. Your EFB combines forecast temperature and pressure altitude to calculate density altitude, which refines your true airspeed estimate and tightens your fuel planning.

How Do I Use Winds Aloft to Choose a Cruise Altitude?

Here’s a worked comparison. Route: Denver to Kansas City, October, Cessna 172, heading roughly due east. Favorable winds come from the west.

Both altitudes show westerly flow - tailwinds on an eastbound leg. The 12,000-foot entry looks attractive: 8 more knots of push. But the full picture includes climb performance.

A loaded 172 climbs roughly 500 feet per minute. From Denver at ~5,300 feet elevation, reaching 12,000 feet costs meaningful fuel and time in the climb. The 12,000-foot tailwind might produce a ground speed of ~140 knots; the 9,000-foot wind might give ~132 knots. On a 400 nm leg, that difference adds up - but so does the fuel burned climbing the extra altitude.

Run the numbers on both. The winds aloft table gives you the inputs; the optimization requires comparing climb fuel, cruise fuel, and time across each candidate altitude.

Should I Check More Than Just My Departure Station?

Yes. Check two or three stations along the route, not just the departure point.

Wind at altitude doesn’t have to be consistent across your entire route of flight. A solid westerly tailwind over Denver can give way to a trough over central Kansas where winds shift and lighten. If you only checked the departure station, you’d miss that entirely. Interpolate for altitudes between the published levels as you build the picture across the route.

How Do I Monitor Winds Aloft During the Flight?

The preflight is half the equation. About 30 minutes into cruise, compare your actual ground speed against what you calculated.

If you planned for a 30-knot tailwind at 12,000 feet and you’re running 10 knots below the expected ground speed, something has changed - the forecast was off, or the winds have shifted. Options include climbing, descending, recalculating fuel math, and updating your ETA. The critical thing is catching it.

Most fuel exhaustion accidents don’t trace back to bad preflight math. They trace back to pilots who stopped cross-checking mid-flight - who let the plan become the reality in their heads when the actual numbers had moved. Build the mid-flight cross-check as a fixed habit.

What Does the Checkride Examiner Expect?

The Airman Certification Standards require you to decode the Winds and Temperatures Aloft Forecast and explain how you used it to select a cruise altitude. The examiner isn’t just verifying the right altitude selection - they want the reasoning behind it.

Walk through the comparison: why does 9,000 beat 12,000 (or vice versa) for this specific route on this specific day? Cover the wind directions, speeds, temperature implications, and climb fuel tradeoff. That reasoning process is what earns the sign-off, not the number alone.

A 15-Minute Pre-Flight Habit Worth Keeping

The night before any cross-country, open the winds aloft table and write down - by hand - the wind direction, speed, and temperature for two or three candidate altitudes at two or three stations along the route. Then run the ground speed and fuel burn numbers for each combination.

It takes about 15 minutes and consistently reveals something that changes the initial altitude pick. No app feature replaces the habit of actually working through the numbers.

Key Takeaways

• The Winds and Temperatures Aloft Forecast is issued four times daily at 0000, 0600, 1200, and 1800Z - always match the product’s valid time to your actual en route window.
• Wind directions are in true degrees, not magnetic. Convert when calculating manually; confirm your EFB does this automatically.
• Decode entries as DDSSTT: direction (×10 for true degrees), speed (knots), temperature (°C). Direction codes ≥51 signal winds over 100 knots.
• No temperature data at 3,000 feet; above FL240, negative signs are omitted from the temperature field.
• Check stations along the full route, not just departure. Cross-check actual ground speed against the forecast 30 minutes into cruise - every time.