March Overview Detailed Climate Perspectives . . . The national temperature index expresses temperature departure from the 60-year mean in terms of standard deviations. Each year's value is computed by standardizing the temperature for each of 344 climate divisions in the U.S. by using their 1931-90 mean and standard deviation, then weighting these divisional values by area. These area-weighted values are then normalized over the period of record.
Positive values indicate warmer than the mean and negative values indicate cooler than the mean.
The preliminary national standardized temperature index ranked March 1999 as the 38th warmest March on record. In contrast, a mean ridge was maintained across the northern plains where above average temperatures were observed. Mild temperatures occurred across the Big Bend area of Texas and portions of northern New England. The temperature anomaly map to the left is based on a blend of surface station data and satellite data. The map to the right shows March 1999 average temperatures as a departure from 1961-1990 station normals.