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Forecast Verification
Published March 24, 2011

Temperature Verification

 (April 2011–September 2011)
Data Source(s): Forecast Evaluation Tool

For a thorough description of the interpretation of these maps, see the feature article, “Evaluating forecasts with the RPSS,” in the April 2009 issue of the Southwest Climate Outlook.

Comparisons of observed temperatures for April–June to forecasts issued in March for the same period suggest that forecasts have been substantially more accurate than a forecast of equal chances (i.e., a 33 percent chance that temperatures will be above, below, or near average) in southern Arizona and New Mexico (Figure 14a). Forecast skill—a measure of the accuracy of the forecast—is highest in southeast Arizona and southwest New Mexico. For the May–July period, forecasts have been better than equal chances in all of Arizona and New Mexico, with the highest RPSS values again in southern regions (Figure 14b). For the three-month lead time, forecasts generally have been more accurate in Arizona but not much better than equal chances in New Mexico (Figure 14c). For the four-month lead time, which spans the monsoon season, forecasts have been much more accurate than equal chances in Arizona and less accurate in New Mexico (Figure 14d). While bluish hues suggest that NOAA–Climate Prediction Center (CPC) historical forecasts have been more accurate than equal chances, caution is advised to users of the seasonal forecasts for regions with reddish colors.

Temperature Verification
Notes:

These maps evaluate the historical performance of the one- to four-month long-lead forecasts made by NOAA’s Climate Prediction Center (CPC). The maps convey the historical accuracy of the CPC forecasts in relation to the reference forecast, which assigns a 33 percent chance to the three CPC categories, “above,” “below,” and “neutral.”  These categories indicate whether conditions are predicted to be similar to the warmest, coolest, or normal temperatures for 1971 to 2000. The maps are generated from the Forecast Evaluation Tool, which was developed by The University of Arizona in partnership with NOAA, NASA, NSF, and the University of California-Irvine.

The maps display the Ranked Probability Skill Score (RPSS). The more the forecasts and actual weather match, the bluer the color. A bluish or reddish RPSS indicates the forecast is more accurate or less accurate, respectively, than assigning a 33 percent chance to each of the three CPC categories.

The RPSS is calculated by comparing all the forecasts made since December 1994 for particular seasons and specified lead times to the actual weather of the season.

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