COMPARISON OF MEAN AREAL PRECIPITATION ESTIMATES FROM WSR-88D AND HISTORICAL GAGE NETWORKS OVER CHEAT RIVER BASIN, WV David Wang, Michael Smith, D.J. Seo Hydrology Laboratory Office of Hydrological Development National Weather Service/NOAA

Objectives n Long term goal is to effectively use NEXGEN data for hydrological forecasting; n Evaluating radar-based MAPX quality over the Cheat River Basin, WV, which is selected as a study basin for Distributed Model Inter-comparison Project (DMIP);

MAPX Calculation n Period:Mar. 1, Dec. 31, 1999 n MAPX are calculated using NEXRAD Stage III data, which are archived at Hydrology Laboratory, NWS; n Stage III HRAP grid are in resolution of 4 X 4 km;

MAP Calculation n Period:Oct. 1, Dec. 31, 1999 n Calculated from the National Climatic Data Center (NCDC) archives; n The domain covered Cheat River Basin has 16 valid hourly gages and 45 daily gages; n Quality control procedures are applied to various stages of calculation by using Interactive Double Mass Analysis (IDMA);

MAP Calculation (cont.) d Daily value for a station is distributed into hourly values based on the nearby hourly observations; Missing values are estimated by 1/d^2; MAP are calculated by multiplying pre- determined weighting factors station observed precipitation;

Radar Coverage over Cheat River Basin

Monthly and annual averaged hourly MAP & MAPX (mm) on different conditions over Cheat River Basin Note:1). Ratio is MAPX/MAP; 2). Missing values are removed from the calculations; 3). Term “unconditional” means MAP>=0 and MAP>=0.

Caption:Red -- Station WV8986 hourly precipitation; Pink -- MAPX time series; Yellow -- Corrected MAPX time series; White -- MAP time series.

Caption:Red -- Station WV8986 hourly precipitation; Pink -- MAPX time series; Yellow -- Corrected MAPX time series; White -- MAP time series.

Caption:Pink -- MAPX time series; Yellow -- Corrected MAPX time series; White -- MAP time series.

Caption:Pink -- MAPX time series; Yellow -- Corrected MAPX time series; White -- MAP time series.

Caption:Pink -- MAPX time series; Yellow -- Corrected MAPX time series; White -- MAP time series.

Caption:Red -- Station WV8986 hourly precipitation; Pink -- MAPX time series; Yellow -- Corrected MAPX time series; White -- MAP time series.

Correction of MAPX time series n Divide MAPX range into 10 section based on the occurrence probability; n Calculate the correction factor for each section (MAP/MAPX) in cold and warm seaon; n Apply correction factors to MAPX time series;

Summary of Results n Long-term annual MAP is in, PRISM annual MAP is in, 4-year averaged MAPX is in; n Radar-based MAPX is under-estimated by about 41% with comparison to MAP; n MAPX time series over Cheat River Basin is usable after correction by multiplying correction factors;