Tuesday, February 21, 2012

Heavy Rain, Avalanches, and Reduced Threat of Lowland Snow

While central and western Puget Sound experienced a nearly rain-free day, very heavy rain has struck the western slopes of the Cascades.    Take a look at the current upper level pattern (see below)--one with a broad ridge over the eastern Pacific and you might think

that nothing much is happening, but such a ridge brings warmer temperatures and strong westerly/northwesterly winds the produce heavy precipitation as they rise on the western slopes of the Olympics and Cascades.  Many such windward locations have had 2-4 inches over the past day, with Spada Lake, northeast of Everett, receiving 5.9 inches in the 24h ending 4 PM today.  Here is the 48-h precipitation from the UW/Seattle Rainwatch system.  Huge amounts, over four inches along the slopes, while practically nothing fell to the SE of the Olympics.  This is a profound rainshadow...the one that usually is over Sequim during southwesterly flow.
Take a look at the precipitation for the last 24h.  A range from .01 inch near Hood Canal to 4.57 inches NW of Everett.  Precipitation was actually lighter over the Cascade crest and then declined to virtually nothing on the eastern slopes of the Cascades.


The snow level has risen to the passes and the effects of heavy rain on the huge snowfall of the past week has set off avalanches, producing EXTREME avalanche danger above 4000 ft.  I repeat extreme.  SR2 and I90 have periodically been closed due to this threat, and in fact Stevens is now closed for the evening.  Such heavy rainfall has resulted in the NWS putting out flood warnings for the Snoqualmie and Tolt Rivers draining the central Cascades, plus the Stillaguamish, Skykomish, and others.

The regional models have indicated this threat for a while; here is the 48h precipitation from a WRF run (our very highest, 1.3 km grid spacing) begun 4 AM on Monday.  Reds indicate over five inches!  And mamma mia...that is quite a rainshadow!

 During the next few days the mountains will get hammered with snow, with the central to northern Cascades getting many more feet.   But what about the lowland snow that folks have been talking about?

The truth is that it is getting less likely, the reason being that the trough over the Pacific is coming in from too westerly a position...not from the NW as associated with most lowland snowstorms in our area.  Here is the latest 72 h upper level forecast (500 hPa).  Not ideal.
It will get cold over the weekend, but a major lowland snow event does not look likely.  Of course, we should watch the situation....

Let me end with some good dog news...no my little dog Leah is still lost in Mountlake Terrace, Brier, and northern LF Park.  But a little beagle named Chunky has been found in the arboretum after being lost for two weeks, after a large effort by Chunky's owners, missingpetpartnership, and others.  We can only hope that someone will see Leah one day...
Chunky...back home again.
Leah--still alive and being spotted.
Remember:  The NW Weather Workshop in Seattle on March 2-3.   See information on the right panel.

11 comments:

Karin Corbin said...

Find us some sunny weather for a major search party to go looking for Leah.

Timothy said...

When do you suppose weather forecasters will get a more pleasing graphical color palette to work with? I always learn a lot reading your posts, maps etc...but the maps themselves are ugly and aesthetically so 1970's.

Is this a function of weathermen not having Raven quality color palettes? I would be happy to give you my map if it helps the cause http://www.goodnaturepublishing.com/lgwatersheds.htm

Best fishes,
Timothy

Alex Mineev said...

Cliff, can you post a link explaining what absolute vorticity means? The images you show say "absolute vorticity". Would be nice to have an explanation of the term. Or may be do a post on this :)

Alex Mineev said...
This comment has been removed by the author.
Unknown said...

I really like the rainfall totals displayed in this blog. I am new to the area and am interested in tracking these totals in real time, but have been unable to find a good source. I'm looking for something with a map, not just a dump of data from some telemetry equipment that is hard to read and talks about locations that I am unfamiliar with. Anybody have any good ideas?

JordanP said...

@Unknown,
Go to Wunderground.com and enter your zip code into the search location. It will bring up the Seattle weather, but if you go the bottom of the page you will see a listing of personal weather stations centered around your zip code.

That page only displays current precipitation rates, not total rainfall, but if you go to most any of the weather station pages they will show the daily and monthly totals and you can select date ranges to see the history.

From any of the personal weather station pages, click on the "View Interactive WunderMap" link under the map on the right. This will give you an expanded map of all the weather stations in your area. It's a great resource if you want to track weather in your neighborhood.

WWH said...

@Unknown - See this page: http://www.wrh.noaa.gov/mesowest/gmap.php?map=sew

Controls on the right panel let you select the type of data you want to display.

Drew said...

We're getting some crazy wind in Yakima right now!

Jenny said...

Cliff,
I read every post on your blog and am so thankful for your accesible, insightful analysis. If I still lived in Washington I would come help you find your dog! Best of luck in your search. My thoughts are with you.

mig said...

My Tacoma neighborhood was a major beneficiary of the recent rain shadow, which we don't get all that often. Combined with the high winds, it helped de-soggify local trails and soccer fields.

Soupman said...

Interesting cloud bank just south of the I90 corridor on the East side. There seems to be a battle between onshore flow and more drier off-shore winds right over this area. This angled bank has been stationery for most of the day so far. Isn't weather fun??