Winds and temperatures are analyzed on a global band grid every 12 hours. The grid is a Mercator projection true at 22 1/2 degrees latitude and extends from 40S to 60N. The first-guess field south of 22N is based on persistence, reverted to climatology. This is primarily due to the sparseness of data over large portions of this region. North of 22N, NOGAPS upper-air analysis fields are used.

Numerous types of data are used in the analysis. Convent ional radiosonde and aircraft reports are used in both the wind and temperature analyses. The wind analysis also includes Pibal reports and satellite derived winds. Vertical temperature profiles obtained from satellite radiometers are used in the temperature analysis. The temperature profiles greatly increase the data base in the Southern Hemisphere.

This analysis uses the same technique as is used in the northern hemisphere upper-air analysis. A major difference is in the amount of satellite data used and the greater weight placed on satellite-derived 1,000- to 300-millibar thickness values.