Home » February 2011 Southwest Climate Outlook » Precipitation Verification
Forecast Verification
Published February 23, 2011

Precipitation Verification

 (March 2011–August 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 precipitation for March–May to forecasts issued in February for the same period suggest that forecasts have only substantially been more accurate than equal chances in parts of Arizona (Figure 15a). Forecast skill—a measure of the accuracy of the forecast—has been highest in southern regions of both Arizona and New Mexico. For the April–June period, forecasts have been less accurate than equal chances in southern parts of both states and near equal chances in other regions (Figure 14b). For the three-month lead time, forecasts have been substantially more accurate than equal chances only in southeast Arizona (Figure 15c). For the four-month lead time, forecasts have been substantially more accurate than equal chances only in southern regions of both states (Figure 15d). Regions with bluish hues suggest that the NOAA–Climate Prediction Center (CPC) forecasts have historically been more accurate than equal chances. However, caution is advised to users of the NOAA–CPC seasonal outlooks for regions where the verification maps display reddish hues.

Precipitation 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 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.

Related Links: