Friday, November 30, 2012

A Look At The Northwest Precipitation Event


I have taken a quick look at the precipitation event that is well underway over the Northwest. Above is blended PW analysis for 3 am MST this morning over the eastern Pacific. A distinct plume of high PW [currently referred to as an atmospheric river (AR) by the community] extends from north and west of Hawaii into northern California, where heavy rains have been occurring at the reporting stations. Heaviest precipitation amounts will occur where the moisture plume intersects higher terrain of the Sierras.


The U of A Atmo WRF-GFS model includes a northwestern US domain and the two products here are from the forecast run (on the 5.4 km grid) initialized at 5 pm MST last evening (Thursday, November 29th). Above is forecast of total precipitation, rain and SWE, for the period ending 5 am MST next Monday morning (December 3rd). Purple shadings indicate amounts of 10 to 20 inches! Image below shows total accumulated snowfall forecast by the model for the same period. In this forecast the darker red shades indicate snow amounts of more than 40 inches. This is quite some event and it is generating weather chatter across the whole country. Meanwhile, down here in the Southwest, November ends having produced only 0.16" of rain here at the house - a tad better than than the 0.02" of October.


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