A 20-year summary of National Weather Service verification results for temperature and precipitation
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A 20-year summary of National Weather Service verification results for temperature and precipitation

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  • NOAA Program & Office:
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    “Trends in the accuracy and skill of National Weather Service forecasts of temperature and precipitation have been analyzed based on a new, 20-year verification archive which is more consistent and homogeneous than data sets which were used in the past. In particular, a subset of verification sites was selected for which data were available throughout most of the period of record. Also, a consistent set of maximum/minimum temperature observations was used to verify the temperature forecasts. Based on this new data set, nationwide average scores were computed both for the locally issued official forecasts and the centrally produced guidance. The verification measures include percent improvement over climate for probability of precipitation forecasts, and mean absolute error and percent of errors >10°F for maximum and minimum temperature forecasts. The results were stratified by forecast projection and season. There is strong evidence that the local and guidance forecasts for both weather elements have improved over the 20-year period from 1966-1986. For example, the overall skill scores for probability of precipitation forecasts during both the warm and cool seasons for all three forecast periods (12-24, 24-36, and 36-48 h projections) show improving trends at or above the 99% level of significance. Similar trends of improving accuracy are evident in the error statistics associated with local and guidance forecasts of temperature for both seasons and for all three forecast periods. In contrast, for most stratifications, our analysis indicates that the accuracy of the longer range (48-60 h) local and guidance temperature forecasts has not improved in a statistically significant manner. However, the lack of a significant trend may be due to the limited length of the time series available for the analysis of the longer range temperature forecasts (1975-1986).”
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