Percent of Normal Rainfall

Another drought aid being produced incorporates products from NOAA/NWS’s Advanced Hydrologic Prediction Service (AHPS). From this service, monthly rainfall deficit/surplus and percentage of normal, updated daily, will be provided to the TV market. The analysis incorporates radar-derived accumulated rainfall, which is bias corrected through validity testing against rain gauge data, as well as the rain gauge data itself, combined into a multisensor field of total rainfall. The data is then compared to a climatological dataset of monthly normal rainfall encompassing observations from 1971-2000. While this product does not truly depict drought conditions, it can be used to communicate the shorter-term trends in rainfall deficit or surplus. The monthly percent of normal rainfall accumulation can be useful to dispel the notion that any single rainfall event has ended a drought. This Percent Normal Rainfall can also explain the great difference in soil moisture in a single region when areas of rainfall surplus border areas of drought. The percent of normal rainfall can be expressed for any time frame, not just monthly, as seen below in the 90, 180, and 365 day percent of normal precipitation maps.