There were several contributors to this beautiful swirl. There was moderate northerly flow in the lower atmosphere (see sounding at Quillayute, on the north Washington coast), resulting in what is called lee troughing (low pressure) on the lee (downstream) side of the terrain. There was also a large amount of horizontal wind shear (change of wind over some horizontal distance) in that region, with strong northerly flow offshore and weak winds near the coast (see weather map plot at 8 AM on Tuesday).
And if you like swirling low pressure, we have had persistent circulations over eastern Washington that have been associated with lots of thunderstorms there the last week. Here is an infrared image for Tuesday afternoon at 4:15 PM--do you see the swirl of thunderstorms over eastern Washington?
Lots of rain over eastern Washington yesterday and today from this circulation. Here are the totals for the last 24h.... substantial amounts, particularly along the fire-prone eastern slopes of the Cascades.
But the real wet story may be coming....here is the forecast 72h precipitation total ending 4 AM next Wednesday....a very wet pattern, indeed, particularly west of the Cascade crest. Stay tuned.
NEWS BULLETIN (courtesy of UW's Mark Albright)
The winter snowpack at Paradise Mt Rainier melted out today (27 May 2015), which is about 6 weeks earlier than normal. This year experienced the 2nd earliest melt-out of the past 99 years. The earliest melt-out date occurred 74 years ago on 24 May 1941. Here are the 5 earliest melt-out dates at Paradise Mt Rainier over the past 99 years from 1917-2015:
1) 24 May 1941
2) 27 May 2015
3) 30 May 2005
4) 1 June 1926
4) 1 June 1934
Announcement: On June 3, I will be on the Seattle Channel's Civic Cocktail with Governor Inslee. If you would like to be in the audience, you can get tickets at: http://www.seattlechannel.org/CivicCocktail. They charge, but you get appetizers with their no-host bar.