National Oceanic and Atmospheric Administration


by Zoltan Toth

In the short, 0 48 hour lead time range forecasts over the Pacific coastal area are adversely affected by the sparsity of in situ observations over the upstream northeast Pacific basin. The relative disadvantage of the west coast areas arising from their geographical location can be ameliorated by enhancements in the observational network over the northeast Pacific. Since additions to the permanent observing network would be prohibitively expensive, research have focused on the use of adaptive observing techniques where data are collected only prior to threatening weather events, and only in areas critical to the development of those events. EMC scientists, in collaboration with university researchers, developed adaptive observational techniques for this purpose. The techniques have been tested in the course of other field programs using NOAA aircraft.

Based on the positive results from the field programs, in 1999 the National Weather Service established the Winter Storm Reconnaissance (WSR) program. This is an annual wintertime program where the NOAA G lV and USAF Reserve C 130 planes collect dropsonde observations for the purpose of improving winter storm forecasts. After streamlining its procedures, the WSR program became operational in 2001. The G-IV operated from Honoulu, HI and Anchorage, AK in January-March, 2002 conducting a total of 155 hours. In the operational WSR program, threatening winter weather events are identified by NWS WFOs, and NCEP Service Centers (primarily HPC). The Senior Duty Meteorologist (SDM) of NCEP collects the requests for extra observations, and through the use of special, ensemble forecast based software, determines the optimal location of the adaptive observations. The request for extra observations are then relayed, through CARCAH, to the NOAA and USAF flight facilities in terms of one or two of the 50 or so predesigned northeast Pacific flight tracks.

The results from seven research and operational field programs indicate that in 70 90% of the cases adaptive observations improve the forecasts for the targeted weather events. On average, a 10 20% error reduction is observed in the targeted forecasts. As a result, numerical forecast guidance issued 48 hours prior to the events become as accurate as 36 hour lead time forecasts without the use of adaptive observations.

Currently, the WSR program runs for a 60 day period each winter, and covers the 24 60 hour forecast lead time range over the Pacific coast. Plans are being developed for the expansion of the program to cover a 120 day period. Also, research planning is underway to explore the expansion of the program to the shorter, 12 24 hour lead time, and smaller spatial scales. With these additions, the WSR program would fulfill, at least during wintertime, the NWS Strategic Goal of "Improved Numerical Weather Prediction (NWP) over the Pacific/West Coast areas".


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