Improved Forecasts of Damaging Pacific Winter Storms



The North Pacific Experiment (NORPEX), conducted jointly by NRL, NOAA, and the USAF during the 1998 winter season, successfully provided the "first line of defense" against El Nino-enhanced winter storms. The mission of NORPEX was to demonstrate that, using sophisticated computer modeling techniques, scientists could identify, in advance, specific areas over the Pacific Ocean where an improved knowledge of atmospheric conditions could lead to improved one to four day forecasts of high impact weather over the United States. These identified "areas of sensitivity" were then targeted as regions for taking special observations of atmospheric profiles of temperature, wind, and moisture. These observations were obtained by deploying dropwindsondes from NOAA's new jet, the Gulfstream-IV, and from U.S. Air Force C-130 planes from the 53rd Weather Reconnaissance Squadron, temporarily based in Alaska and Hawaii. The additional data obtained along each flight was immediately transmitted back to the National Weather Service and U.S. Navy operational forecast centers in real time for incorporation into their computer forecasting models.

3D Targeted Observing Missions. Postexperiment analyses conducted as part of NRL's research on atmospheric predictability indicate that the NORPEX aircraft observations produced major changes in the intensity and track of the jet stream and the major winter storm systems. These changes led to significant improvements in the accuracy of forecasts and warnings for land-falling storms along the U.S. West Coast.

In addition, extended-range forecasts for severe storms in the central and eastern U.S. were also improved by the NORPEX observations up to 4 days in advance. The observations collected in NORPEX represent an unprecedented effort to improve prediction of storms that often develop in areas devoid of most meteorological data. Our capability to pinpoint areas of forecast sensitivity is extremely important for making the most effective use of the relatively few measurements that can be taken over an area as vast as the North Pacific Ocean. These observations of early storm structure are essential for providing the public with improved advance warnings of storm landfall, rain and snow amounts, and flooding potential.


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