EXTREME WEST COAST PRECIPITATION EVENTS

Winter storms bringing heavy rain, mountain snow, and widespread flooding are the severe weather of the West. For example, in terms of property damage, two of the top twenty storms to strike the United States in the last five years (1995-1999) were flooding events on the West Coast; a storm in 1996 in northern Oregon with $400 million in damage ranked 15th, while in 1997 a similar storm in northern California had $330 million in damage and ranked 18th. These severe events are the combination of a persistent synoptic storm track entraining a high moisture content air stream from the sub-tropics, and strong mesoscale and terrain influences.

Despite considerable advances in our understanding of the salient processes and nearly continuous increases in overall skill in operational numerical weather prediction and data assimilation, quantitative precipitation forecast skill is lagging. This limited progress can be linked to several areas, including poor upstream initialization, inadequate model grid resolution, and poor model microphysics. Fortunately, an arsenal of ongoing efforts within both the research community and NOAA is providing the promise of a brighter future.

An effort will be made in this presentation to illustrate these current inadequacies and then provide a general overview of the current and planned research targeting these problems. Particular emphasis will be placed on results from a leading, real-time high-resolution modeling effort staged in the Pacific Northwest. After several years of development, this system is providing unique results that are highly illustrative of the most pressing scientific issues.