An example of the HPC moisture flux tool during the 18-20 December 2010 atmospheric river event over California. Click image for more detail

HPC Western Region 7-day QPF is now available twice daily through 30 April 2012 Contact:  Ed Danaher

HMT-West Findings Helped Forecast Heavy Rains in the Western U.S.

As a series of storms over the Pacific Ocean in December 2010 threatened to bring a prolonged period of heavy rainfall to the western United States, NOAA's Hydrometeorological Prediction Center (HPC) was asked to provide additional forecast support.

HPC typically provides quantitative precipitation forecast (QPF) guidance for the continental U.S. up to 5 days (120 hours) in advance. For this event, HPC extended their QPFs to include 6-7 days (144-168 hours) in advance for NWS Western Region, which covers the area west of the Rocky Mountains. These forecasts were so successful that HPC was asked to continue issuing the extended guidance throughout the winter.

These extended forecasts were made possible in large part due to research findings on water vapor transport associated with Pacific Atmospheric Rivers (ARs) from NOAA's Hydrometeorology Testbed (HMT), including activities in HMT-West and HMT-HPC. A few months prior to this event, HPC forecasters participated in two Virtual Institute for Satellite Integration Training sessions hosted by HMT-West scientists that highlighted the diagnosis, structure and tracking of water vapor fluxes associated with ARs using satellite data. HPC forecasters used information from this training as well as normalized anomalies of model moisture transport at 850 hPa to gauge the magnitude of AR events and their contribution to heavy rainfall in their preparation of the extended QPFs.

HPC continues to work with HMT to further improve the forecasting of rainfall associated with landfalling AR events. A second scientist will be added at HPC through HMT funding to support HMT-West work on these long-lead forecasts.