Winds Aloft – Issued 4 times daily (0600Z – 1200Z – 1800Z – 2400Z)
Winds Aloft is a very important weather product used primarily for cross-country planning (also useful for detecting temperature inversions aloft). Winds Aloft is a forecast product that will provide you with: Wind Direction, Wind Speed, and Temperature for the selected altitudes. Here is an example of a Winds Aloft chart:

000
FBUS31 KWNO 050158
FD1US1
DATA BASED ON 050000Z
VALID 050600Z FOR USE 0200-0900Z. TEMPS NEG ABV 24000



CGI
3007
2810-12
2615-14
2520-18
2434-30
2362-39
228547
236948
235849


EVV
3206
2511-11
2518-14
2325-17
2251-27
7303-36
711849
229850
237349


SPI
2514
2620-13
2618-15
2617-20
2720-30
2921-42
234449
235248
244849


STL
2611
2615-13
2616-15
2715-19
3112-30
3119-41
244049
244647
254448

The header for Winds Aloft contains basic information to verify that the information provided is still valid. For the above example, the header states that the data provided is based on computer forecasts generated on the 5th day of the month at 0000Z. The next line provides you with the validity period for this specific winds aloft. This winds aloft is valid on the 5th day of the month at 0600Z and is for use between 0200Z and 0900Z.

The first column shows the station identifier for which the winds are forecasted. The next column is the winds aloft at the 3,000 foot level (MSL).  The first two numbers are the direction of the wind rounded off and the following two numbers are the temperature. For CGI (Cape Girardeau), the winds at 3,000 feet are 300° at 6 knots. For altitudes higher than 2,500 feet AGL, the temperature is added as the last two letters. At CGI but for 6,000 feet (the third column), the wind is out of 280° at 10 knots and the outside air temperature (OAT) is 12°C. Above 24,000 feet, it is always assumed that the OAT is negative.

Because winds are often greater than 100 knots at higher altitudes, a system was developed to denote this on the Winds Aloft chart. In the above example, you can see that for Evansville (EVV) at 24,000 feet the winds aloft are: 711849. Obviously the winds can’t possibly be coming out of 710°, and it is highly doubtful that the winds are at 18 knots that high up. If the wind direction is ever greater than 36 (representing 360°) than you have to subtract 50 to get the wind direction and add 100 to the wind velocity. So for EVV, 711849, the winds are out of 210° at 118 knots and the OAT is -49°C (Remember, the temperature is assumed to be negative above 24,000 feet. So in this case, the OAT is -49°C).

—–

Resources: For more detailed information, check out the FAA published book: Aviation Weather Services. This book contains all the information about every weather service available for pilots. This book is a valuable resource when it comes to studying for checkrides or trying to decipher the more uncommon weather products. Click on the book below to find out more.