89th American Meteorological Society Annual Meeting

Sunday, 11 January 2009
Evaluation of the Environmental Protection Agency / National Weather Service Ultraviolet Index forecast against independent UV measurements: Phoenix Arizona (2000-2006)
Phoenix Convention Center
Jessica M. Nolte, NOAA/NWS, Phoenix, AZ; and K. DeBiasse and B. M. Svoma
The effectiveness of the National Weather Service (NWS) Ultraviolet Index (UVI) forecast is evaluated for Phoenix Arizona, one of the largest U.S. metropolitan areas that annually experiences exceedingly large dosages of UV radiation. Data were collected from Arizona Desert Testing LLC sited at Wittmann AZ, the Volkswagen (VW) Arizona Proving Grounds sited at Maricopa AZ and Atlas Material Testing Technology LLC, DSET Laboratories sited at New River AZ. The greatest distance observed between any of the observing stations is 96 km (New River to Maricopa) with the forecast point centrally located near the Phoenix urban center. In general, over sixty percent of the variance in UV radiation is shared between the three independent facilities' data although the geographic distances between sites are relatively large. Overall correlations between the NWS UVI forecasts and the three independent testing facilities' data are relatively weak when the annual cycle is removed from all datasets. Only twenty-five percent of the variance in UV data is accounted for by the NWS UVI forecast. To account for lower correlations, we considered two meteorological parameters, daily sky cover and air quality observations of PM10. We found that greater sky cover and high amounts of PM10 are likely the reasons for such low correspondence between UVI and UV data in June. Optical depth may need to be better incorporated in the NWS UVI forecast process through pollution forecasts in order to increase the correspondence between the NWS UVI and actual UV irradiance. Finally, we considered the issuance of heat products from the NWSFO-Phoenix for the period from 2003 to 2006 and found that the NWS UVI was higher (p=0.081) for days with an issued heat product. This would suggest that perhaps a statement involving the NWS UVI forecast be added to the heat products for Phoenix, Arizona.

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