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Forecast Verification
Published October 27, 2010

Temperature Verification

 (November 2010–April 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 November–January to forecasts issued in October for the same period suggest that forecasts have been more accurate than forecasting equal chances (i.e., 33 percent chance that temperature will be above-, below-, or near-average) only in southeast and northwest Arizona and southwest New Mexico (Figure 12a). Outside of southern Arizona and New Mexico and northwest Arizona, forecast skill—a measure of the accuracy of the forecast—is similar to an equal chances forecast. For the December–February period, forecasts outside of northwest Arizona have not been better than equal chances in all of Arizona and New Mexico (Figure 12b). For the three-month and four-month lead times, forecasts issued in October have been more accurate than equal chances in many areas of the Southwest (Figures 12c–d).  While bluish hues suggest that 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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