Wednesday, November 11, 2015

Potent Atmospheric River Will Reach the Northwest Tomorrow

If this blog had music, you would hear the JAWS theme in the background (click here if you want the audio).

A very potent Westerly Atmospheric River (WAR) event is coming, with heavy rain and flooding.  Another drought-buster event that will fill our reservoirs.  And there is more:  plenty of wind and high surf on our ocean beaches.

A recent infrared satellite image shows a plume of high clouds associated with the approaching moisture and strong winds (see below).


 And the latest UW WRF forecast for Thursday night at 7 PM shows the high moisture value (red colors) aimed right for us.  It looks like a fist.  This is an example of an atmospheric river, a plume of large moisture values, but it is not a pineapple express--those events bring moisture from the southwest near Hawaii. In this case moisture is streaming northward over the western Pacific and then heading nearly due east towards us, Westerly Atmospheric River.

This moisture plume is associated with strong westerly wind sand when the moist air is forced to rise by our regional terrain the result will be very heavy precipitation.  To illustrate, here is the Washington State 48h precipitation ending 4 AM on Saturday.  Broad areas with 5-10 inches and some exceeding 10 inches. That is serious folks.

The following  72 hours brings more, with the Oregon Cascades getting hit hard as the atmospheric river moves south.  Even California and its thirsty reservoirs will get a piece of this action.


The NOAA/NWS River Forecast Center is predicting flooding on many western WA rivers, several reaching moderate flood levels (see below).  So be careful in the normal flood-prone spots.


Now I know my snow loving friends are getting nervous about this atmospheric river event.  

Atmospheric rivers usually bring warm rain through elevation, which is not exactly good for snow.   That is true...but this case is not a pineapple express so temps will be a bit cooler and the period of warmth will be relatively short (about 36h).   The snowpack will be knocked back a bit at lower elevations, but some of the rain will freeze in the snow.  And higher elevations will have a net snow gain.   Let me show you.

The UW WRF model suggests that  next 72 still bring some snow to the higher elevations (see below)

But the exciting thing is that after the atmospheric river passes through on Monday, we moved into colder air with lots of shower activity....and large amounts of snow (see below for snowfall for 72 hr ending 4 PM Wednesday). Feet of snow over the entire Cascade Range.  Ski season begins.

Finally, the strong winds working on a long fetch over the ocean, coupled with some big storms offshore, will bring big waves to the coast...some getting up to 20 feet.  The NOAA Wavewatch III model suggests that later on Friday there could be 7 meter (around 23 ft) waves hitting the central WA coast.  Good wave watching at Westport.


16 comments:

John Nelson said...

I'm one of those snow level friends. Looks ominous in the next few days, but it's all part of the base-building process! The season is already looking better than last year.

Craig Armstrong said...

I'm excited to go to Ocean Shores this weekend! Love it stormy on the coast.

Upupaepops said...

there are some black clouds out their tonight

Scott K. said...

Cool storm, but looks like a bit of a dud for the puget sound region (seattle and surrounding) due to the rain shadow from the olympics.

Gpacharlie said...

Watch out for logs at the beach.

spappyjones said...

JR WX PRTL BULLITEN:
.SHORT TERM...A WET FLOOD-PRODUCING ATMOSPHERIC RIVER EVENT WILL BE SETTING UP ON THU AND LASTING
UNTIL SAT MORNING. STRONG SAND WIND POSSIBLE. THE PATTERN IS BEING BEING AIDED BY THE DEVELOPMENT OF A STRONG AND CONSOLIDATED
UPPER JET STREAM OVER THE NE PAC WITH A SAND WIND FEATURE...TO THE SOUTH OF A VERY DEEP 965 MB LOW CENTERED NEAR
KODIAK ISLAND ALASKA WITH LOTS OF SAND AND WIND SOME WATER. WATER VAPOR IMAGERY SHOWS THE JET TAPPING INTO A TROPICAL MOISTURE SOURCE
ALL THE WAY BACK NEAR GUAM AND LOTS OF SAND UPLIFT INTO THE JET. THE LEADING NOSE OF THE JET WILL REACH THE B.C. COAST ON THU MORNING...
INITIALLY PUSHING AN ENERGETIC WARM SAND WIND ACROSS WRN WA. THIS WILL SIGNAL THE START OF OUR RAIN/SAND EVENT...
ALONG WITH A SIGNIFICANT INCREASE IN S-SE PRESSURE GRADIENTS AND WIND SAND.

The Outfield said...

spappyjones,

What is all the talk about sand in the jetstream?

James Lagergren said...

The killer logs!

Anne said...

It refers to a humorous typo in Cliff's original post

Westside guy said...

Yeah, I thought originally that was just a typo in Cliff's blog - this is the first time I recall hearing that term. It'd be Interesting to learn more about this "sand wind" and the jet stream.

Richard Fuhr said...

Cliff wrote: . In this case moisture is streaming northward over the western Pacific and then heading nearly due west towards us, Westerly Atmospheric River. but didn't he mean to write due east

jno62 said...

I'll keep my excitement in check until I see evidence.

We were supposed to get 18 inches of snow this week, yet............

Chris Shotwell said...

Quite the rain shadow right now. Any idea when the donut might close down on Seattle?

Gpacharlie said...

Major SAnD storms caused by climate change

But seriously this looks like a lot of wet coming.

Ansel said...

Guys,

Yes I think he meant to write "winds and..." not: "wind sand..." a keystroke sequence error.

Scott K. said...

@Chris Shotwell,

That's what I noticed too (and mentioned in an earlier comment). Based on the data Cliff provided, it looks like a bit of a dud for the Seattle area or the areas around lake washington (eastside, north to lynnwood, south to tacoma).

Impressive forecast rain totals for the mountains and peninsula, but not much going on elsewhere.