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Forecast Verification
Published June 20, 2011

Precipitation Verification

 (July 2011-December 2011)

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 precipitation for July–September, which spans the monsoon season, to forecasts issued in June for the same period suggest that forecasts are less accurate than equal chances in all of Arizona and New Mexico (Figure 15a). Forecasts have not fared well for this time period in regions most influenced by the monsoon, such as southwest New Mexico and southeast Arizona. For August–October, forecasts have been less accurate than equal chances in most of the Southwest, with the exception of southeast Arizona (Figure 15b). For the three-month lead time, forecasts have been similar to or less accurate than equal chances in most of both states (Figure 15c). For the four-month lead time, forecasts have shown better accuracy than equal chances in southern Arizona (Figure 15d). Regions with bluish hues suggest that the NOAA–Climate Prediction Center (CPC) forecasts historically have been more accurate than equal chances. However, caution is advised to users of the CPC seasonal outlooks for regions where the verification maps display reddish hues.

precipitation verification of United states from July 2011 to December 2011
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 wettest, driest, or normal precipitation 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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