Turn Around Winds

(Mean Zonal Winds)

During the winter our balloons generally head in an easterly direction. However during the summer months we must be careful that we do not launch too close to the foothills or we might lose a payload by its flying towards the west and landing in the mountains.

Ok, you are always hearing about it but when and how much do the winds at high altitude reverse direction.

Below are several charts of the winds aloft at various latitudes and altitudes for each month of the year. These charts do not show the exact direction of the winds rather, they shows if they are moving out of the west as positive numbers or as occurs in the summer months, out of the east as shown by negative numbers.

The X axis is the month (1 = Jan, 2 = Feb, etc.)

30� North Latitude

35� North Latitude

40� North Latitude

45� North Latitude

50� North Latitude

This turn around Generally occurs above 57,000 feet.  However there are minor variations with each latitude. The winds start to change direction as early as April and revert to their westerly flow as late as October.

Data for these charts was obtained from:

COSPAR International Reference Atmosphere: 1986 (0 km to 120 km)

If you live at a different latitude and want to generate your own data here is a spreadsheet:

This file runs around 238 Kbytes and contains the mean zonal winds for latitudes 80� South to 80� North for all 12 months of the year at various altitude levels from the surface to space (117 kilometers altitude). Balloon groups won't be interested in much above 30 kilometers but, the data was there and so I've left it in. This data was gathered and processed in 1986.

In order to get just those winds for each latitude I imported the file into Access and used that database program to pull out only the records I was interested in.

Ralph Wallio has done an in depth study of this phenomena  and his results (obtained with newer data) are available at: