Monday, February 2, 2015

The West Coast Atmospheric Faucet Turns On: Will it Save California?

During the past month, precipitation has been near normal over Washington, but substantially drier than normal over Oregon and California (see graphic).   Last month, San Francisco had their driest January on record: NO PRECIPITATION.  One major storm brought some water to California's reservoirs in December: helpful, but a literal "drop in the bucket" for what they need.   In addition, the subsurface water content is very low, with agriculture drawing heavily from critical aquifers.

Things may be looking up for Oregon and California: a very, very wet weather event is about to happen.

Let's look at the WRF model forecast for precipitation  over the next 72h (starting 4 PM this afternoon).   Fairly wet from the Bay Area to British Columbia, with a number of western slopes getting 2-5 inches.  This is the warm up, or better described as the pre-soaking. Enough to get the river levels up, but with little or no flooding.

And then it gets serious, particularly in northern Californi, when a very strong atmospheric river hits the region.  You see the white colors--that is 10-20 inches of rain.  Expect flooding in northern California and a massive refilling of the critical...and large...northern reservoirs.  This is the storm that may prevent water disaster this year.

For stage 1 of this event, a weak atmospheric river will aim for the Pacific Northwest (the color shading shows the water vapor content of the atmosphere).

but then the main course arrives and the most dramatic atmospheric river in over a year will strike northern California.  Serious stuff.  These atmospheric rivers are going to be warm, so very little snow south of the central Cascades.  Sorry Oregon.  The Sierra Nevada will get snow at higher elevations.

The origin of all this water fun is from a strong, warm, southwesterly wind current that will develop in the eastern Pacific.  Here is the forecast map for 500 hPa (about 18,000 ft) on Friday at 8 AM.  The winds are parallel to the height lines and winds are stronger when they are closer together.  Trust me, this is a very wet pattern for the West Coast.

And did I mention the several strong Pacific cyclones that will  approach are region during the period (like the one below, showing isobars--pressure--and wind speed--shaded)?   I better not...

The Pacific Northwest Weather Workshop

Interested in attending the big local weather workshop of the region?  The Pacific Northwest Weather Workshop will be held in Seattle at the NOAA facility on February 27-28th.   Everyone is invited and the majority of talks are accessible to laypeople.  To attend you have to register or they won't let you in the gate.  There will be a major session on the Oso landslide.  There is a registration fee that covers refreshments and food, and special student pricing.  If interested, check out this website.

Climate Change and the Pacific Northwest

I will be giving a provocative talk on this subject on March 11th at 7:30 PM Kane Hall on the UW campus in Seattle.  Sponsored by local public radio station KPLU, tickets for this event can be secured at this web site.


Ansel said...

So will it be cold enough so we get some mountain snow?

I went cross-country skiing around the Lake Wenatchee-Nason Ridge area last weekend. There was barely enough snow to make it possible. Bare spots at 3300 feet and below.

What about lowland snow this year... Unlikely, I presume?

CP Grosenick said...

Check out the Methow Valley. Lots of great Nordic skiing and downhill up at Loup Loup Ski Bowl 15 mins from Twisp

Marcus said...

Of everything in this post, I was most intrigued by the first graphic, and the big blue dot in the Idaho panhandle. Any thoughts why that one locale has seen such a big (positive) anomaly compared to everywhere else in the West?