Finally! Heavy Rain, Wind, and Snow Headed for the Pacific Northwest AND California

After an unusually dry first half of November in the Northwest and northern California, everything is going to change this week, as drenching rain hits California, substantial snow blankets the Cascades, and a minor windstorm strikes northwest Washington late on Thanksgiving day.

Let me start by showing you the total precipitation forecast to fall during the next 6 days from the UW WRF modeling system.     Northern California, including the area of the Camp Fires, is going going to be hit hard, with 5-10 inches in some areas.  This rain should help bring the fires under control and potentially set the stage for slope failures and flooding.  Substantial, but more moderate, rain will be received over the western side of Oregon and Washington.

Let me show you the day by day rainfall totals.  The situation will be dry through early Wednesday.
The 24h amounts ending 4 AM Thursday shows a wet West Coast, with lots of rain in northern CA.

More of the same for the next 24h, with northern CA getting 2-5 inches and about half that over the WA Cascades and Olympics.

So expect a wet Thanksgiving.  And perhaps a windy one over NW Washington!  The forecast sea level pressure map valid 7 PM Thursday shows a strong low pressure center making landfall on southern Vancouver Island.  If correct, this storm will bring strong winds to the WA/OR coast Thursday afternoon and evening, with NW Washington having gusty condition during the afternoon and evening.   Thanksgivings are notorious for these kinds of storms.

And what about snow?   Don't worry!  The 72h totals ending 4 PM Sunday suggests 1-2 feet about roughly 3500 ft in the Cascades.

So why the big change?  Because of a major change in the large scale atmospheric circulation over the western U.S.

At  1 PM today, a big ridge of high pressure is over the U.S. West Coast.

By Tuesday morning the ridge of high pressure moves inland and an elongated trough has moved in off the West Coast.

The trough, which brings clouds and precipitation reaches the coast by 4 PM Wednesday.

 And Thursday at 7 PM, strong flow pushes into the west coast (winds are parallel to the height lines, with strong winds where the lines are closest together).

In short, a radical change in weather from the past few weeks that will end wildfires, restore our air quality, bring needed water to the West, but bring some hazards (strong winds, slides, localized flooding).



from Cliff Mass Weather and Climate Blog https://ift.tt/2FrPm37