The 5–9 February 1996 Flooding Event over the Pacific Northwest: Sensitivity Studies and Evaluation of the MM5 Precipitation Forecasts

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Abstract
This paper describes the flooding event of 5–9 February 1996 in which a series of landfalling Pacific storms brought 30–70 cm of rain to many mountain sites over southwest Washington and northwest Oregon. This event was simulated at 36-, 12-, 4-, and 1.33-km horizontal resolution using the Pennsylvania State University–National Center for Atmospheric Research mesoscale model (MM5). The model precipitation was verified with over 300 rain gauges in western Washington and Oregon as well as WSR-88D radar data from Portland, Oregon. There was a significant improvement in the precipitation forecast skill as the grid spacing was decreased from 36 to 4 km; however, the 12- and 4-km resolutions had excessive precipitation shadowing in the lee of barriers. Although increasing resolution from 4 to 1.33 km did not produce a significant improvement in precipitation skill for the entire domain, the 1.33-km domain had more precipitation in the immediate lee of the Cascades, and thus verified better in those reg... Abstract This paper describes the flooding event of 5–9 February 1996 in which a series of landfalling Pacific storms brought 30–70 cm of rain to many mountain sites over southwest Washington and northwest Oregon. This event was simulated at 36-, 12-, 4-, and 1.33-km horizontal resolution using the Pennsylvania State University–National Center for Atmospheric Research mesoscale model (MM5). The model precipitation was verified with over 300 rain gauges in western Washington and Oregon as well as WSR-88D radar data from Portland, Oregon. There was a significant improvement in the precipitation forecast skill as the grid spacing was decreased from 36 to 4 km; however, the 12- and 4-km resolutions had excessive precipitation shadowing in the lee of barriers. Although increasing resolution from 4 to 1.33 km did not produce a significant improvement in precipitation skill for the entire domain, the 1.33-km domain had more precipitation in the immediate lee of the Cascades, and thus verified better in those reg...

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