The winds aloft forecast and the headwind hiding at your planned cruising altitude

The winds aloft forecast is the single most important factor in choosing your cruising altitude, calculating fuel burn, and determining whether you’ll make your fuel stop comfortably or land on fumes. Yet most student pilots treat it as a box to check rather than a planning tool. Understanding how to read and apply this forecast will fundamentally change how you plan every cross-country flight.

What Is the Winds Aloft Forecast?

The winds aloft forecast is abbreviated FD (forecast winds and temperatures aloft). You may also see it called FB winds or listed as “winds and temperatures aloft forecast” on 1800wxbrief or in ForeFlight. Same product, different labels.

The National Weather Service issues this forecast twice daily, based on 00Z and 12Z. It provides wind direction, wind speed, and temperature at fixed altitudes above mean sea level: 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 feet. For most general aviation pilots, the relevant altitudes are 3,000 through 12,000 feet.

How Do You Decode the Winds Aloft Format?

The format looks like a jumble of numbers until you know the pattern. Take the string 2135+07 as an example:

• 21 — Wind direction in tens of degrees. So 21 means 210 degrees.
• 35 — Wind speed in knots. 35 knots.
• +07 — Temperature in Celsius. +7°C.

That’s it: 210° at 35 knots, temperature +7°C.

Three encoding tricks trip people up:

Winds over 100 knots. When wind speed exceeds 100 knots (common at higher altitudes), 50 is added to the direction code and 100 is subtracted from the speed. If you see 7308, subtract 50 from 73 to get 23 (direction 230°), then add 100 to 08 for 108 knots. You likely won’t encounter this below 18,000 feet, but it does appear on knowledge tests.

Light and variable. The code 9900 means winds are less than 5 knots with no consistent direction. This is good news — wind at that altitude is essentially a non-factor for groundspeed.

Missing 3,000-foot data. No wind is reported at the 3,000-foot level for stations where the station elevation is within 1,500 feet of that altitude. Surface-proximity winds are unreliable from upper-air models. Flying out of Denver? Don’t expect a 3,000-foot wind — and you may not get a 6,000-foot wind either, since the field elevation already exceeds 5,000 feet.

How Do Winds Aloft Affect Your Altitude Choice and Fuel Burn?

Consider this scenario: a 300 nautical mile cross-country from central Texas to southern Kansas. Your airplane cruises at 110 knots TAS with 4 hours of fuel and no planned fuel stop.

At 6,000 feet, winds along the route are from the south at 10 knots — roughly a tailwind on your northbound heading. Groundspeed: approximately 120 knots. Flight time: about 2.5 hours. Fuel is comfortable.

At 9,000 feet, winds shift to the southwest at 25 knots. The crosswind component eats into groundspeed, plus the westerly angle introduces a headwind component. Groundspeed drops to roughly 95 knots. Flight time: over 3 hours. Your fuel reserve just shrank dramatically.

Same airplane, same day, same route. One altitude gives you a comfortable margin. The other has you landing with minimal reserves. This is why the winds aloft forecast matters.

What Does the Examiner Expect You to Know?

The Airman Certification Standards require you to select an appropriate altitude considering winds aloft, terrain, weather, and airspace. The word “appropriate” carries weight — it means you analyzed the winds, calculated their effect on groundspeed and fuel burn, and made a deliberate choice.

A weak answer on the checkride: “I picked this altitude because it’s above 3,000 AGL and below Class Bravo.”

A strong answer: “The winds at 6,000 give me a 15-knot tailwind I don’t get at 8,000, saving me 20 minutes and 3 gallons of fuel on this leg.” That demonstrates you actually used the forecast.

How Do Winds Aloft Temperatures Affect Your Flight?

The temperature data in the forecast does more than fill a column. True airspeed changes with temperature and altitude. On a standard day at 6,000 feet, your TAS might be 110 knots. If the actual temperature is 10°C warmer than standard, TAS increases slightly. Colder than standard, it decreases. The difference may be only 3–4 knots, but over a long leg it adds up.

For instrument-rated pilots or anyone flying near clouds, temperature also reveals icing potential. If the temperature at your planned altitude falls between 0°C and –20°C and there’s visible moisture, you’re in the icing zone. Combine this with the freezing level from your area forecast and you have a much clearer picture of where you can and cannot safely fly.

What Are the Most Common Winds Aloft Planning Mistakes?

Checking only your departure station. The wind at your departure might be calm at 9,000 feet, but the wind at your destination could be 40 knots from the northwest. Pressure gradients change across distance. Check stations along your entire route, not just where you’re starting.

Picking altitude before checking winds. Many students choose 6,500 feet because it’s the correct VFR hemispherical cruising altitude for their heading, then discover they’ve got a 30-knot headwind. The next legal altitude at 8,500 might be better — or worse. You won’t know until you look.

The better approach: Pull the winds aloft first. Examine every available altitude from 3,000 through 12,000 feet. Identify where the winds favor you. Then choose your altitude based on wind advantage, hemispherical rules, terrain clearance, and weather — in that order.

How Do You Apply This on a Real Flight?

Suppose you’re flying east from Phoenix to El Paso. Magnetic course is roughly 090°, so VFR hemispherical rules give you odd altitudes plus 500: 5,500, 7,500, or 9,500 feet.

The winds aloft show:

• 6,000 feet: West wind at 15 knots (direct tailwind), temperature +8°C
• 9,000 feet: West wind at 30 knots (stronger tailwind), temperature –3°C

At 9,500 feet, you get a bigger tailwind and better fuel economy. But at –3°C, any moisture means potential icing on the climb. At 5,500 feet, you still get a tailwind, stay warm, and avoid icing risk.

If skies are clear, 9,500 is the better play. If buildups or cloud layers sit between you and 9,000, 5,500 is the safer, smarter choice. That kind of decision-making is exactly what the winds aloft forecast enables.

Where Can You Find and Visualize Winds Aloft Data?

The standard briefing from Flight Service or 1800wxbrief includes winds aloft data. Apps like ForeFlight and Garmin Pilot display the same data graphically with wind barbs on the map, letting you scrub through altitudes and see the wind field at each level. Use whichever format works for you — but use it.

When stations along your route don’t line up perfectly, interpolate between them. If one station reports the 9,000-foot wind from the west at 20 knots and the next station says 30 knots, estimate roughly 25 knots at the midpoint.

How Do You Build Better Wind Judgment Over Time?

After every cross-country, compare the forecast to what you actually experienced. Check your GPS groundspeed during cruise and work backward. If the forecast predicted a 15-knot tailwind but your groundspeed suggested a 5-knot headwind, note the discrepancy. Over time, you’ll develop an instinct for how much to trust the forecast and how much margin to add.

The source material for all of this comes from AC 00-45H (Aviation Weather Services) and the Pilot’s Handbook of Aeronautical Knowledge weather chapters, both available free from the FAA.

Key Takeaways

• The winds aloft forecast (FD) is your primary tool for altitude selection and fuel planning — not an afterthought in your weather briefing
• Check winds at every available altitude from 3,000 to 12,000 feet before committing to a cruising altitude
• Decode the format: first two digits are direction (×10), next two are speed in knots, and the final group is temperature in Celsius
• Examine stations along your entire route, not just your departure point — winds can change dramatically over distance
• Compare forecast to actual groundspeed after each flight to build judgment about forecast reliability