Saturday, November 17, 2012

Superfront followed by Big Rain

It's the end of November and time for serious storm watching.  And our high-tech observing tools provide a good view  (and lots of warning) about what will occur.  And the latest model runs suggest the next week will be extraordinarily wet.  Perhaps dangerously wet.

Let's start with this morning's impressive infrared satellite image (8 AM).  A strong Pacific front is immediately offshore (the linear north-south feature) and connects with an occluded front that extends out into the Pacific into a well-defined Pacific low between northern Vancouver Is. and the Queen Charlottes.  To the south of the low is a comma cloud, that is associated with upper level disturbance.


There is a very well-defined, strong surface front embedded in the frontal zone and we can watch it approach using our new Langley Hill radar.  Here is a sequence of images starting at 4 AM and ending just after 9 AM (you can click on them to blow them up).  You see the thin line of enhanced radar reflectivity (reddish or dark yellow)?   That is the surface cold front.  There is a narrow cold frontal rain band there and if you look carefully you can see that it is corrugated with stronger and weaker segments.   A zone of less intense rain follows.





There were big changes as the surface front moved through:  pressure rise, temperature fall, wind direction shift.   Here is what happened at the Destruction Is. buoy right off the central WA coast for temperature and pressure:  big drop in temperature and large rise in pressure.  The wind also shifted from southerly to westerly (not shown). 



We will get some moderate rain with this front.  And then there will be a only some showers until Sunday evening when a stronger front will come through, followed by an even wetter system on Monday.  Take a look at the totals for the 72 hours ending Tuesday at 4 AM (graphic below).  Many of the mountains areas around here will get 5-10 inches of precipitation.  Over 10 inches near the CA/OR border.    There will be a lot of snow at higher elevations (particularly above 3500 ft for the first two fronts, but it will be getting warm on Monday and thus the snow level will rise above the lower passes when the precipitation is hardest...sorry.   Mt. Baker and Crystal should be able to open.  Don't ask about Snoqualmie. 

Finally, I hate to mention this, but the latest model runs are suggesting the potential for a major precipitation/flood event on Thursday/Friday.  The ground will be saturated from the earlier rains and then a persistent atmosphere river just stays over us.  Lots of uncertainty this far out, but here is the 48-h precipitation forecast ending 4 PM on Friday. Over 10 inches in the Olympics. 

Take a look at the total precipitation for the next 192 hr (through Sunday at 4 AM) from the National Weather Service GFS model.  Unbelievable. 20-25 inches over the Cascades...and this is a low resolution model that will not get the true magnitudes of the mountain precipitation).   If you live near any of the major rivers around here, you better stay tuned.  FEMA should watch this as well.



10 comments:

windlover said...

Yikes! Thanks for the heads up Cliff! Hopefully everyone that lives in an area that is prone to flooding &/or will be traveling will pay close attention to the weather updates as the days go on and prepare as needed! Stay safe everyone!

Buddy said...

The 192hr map is incredible. These first few storms have been forecasted consistantly. Very good. But the pineapple express event just recently showed up. You're the one who taught us not to get very excited 4-5 days out on one particular model.

C&A said...

Cliff, The NWS Seattle forecast discussion was still downplaying flood risk last I looked... I take it you're disagreeing?

So glad I cleared a few problem gutters yesterday!

Unknown said...

It's not the Pineapple Express, it's the Kuril Kannonball.

Charlie Phillips said...

There is still a bit of uncertainty with the Thanksgiving/Black Friday front... but the 12z WRF sure painted a wet scenario for Washington. How would this compare to November 5-7, 2006?

h said...

hey cliff i don't know what the protocol is for meteorological usage of geographic names, but the queen charlotte islands have been called Haida Gwaii for a few years now in BC

"On June 3, 2010, the Haida Gwaii Reconciliation Act officially renamed the islands Haida Gwaii as part of a reconciliation protocol between British Columbia and the Haida people."

(from http://en.wikipedia.org/wiki/Queen_Charlotte_Islands )

David B. said...

Yikes... definitely sounds like enough rain to flood I-5 and the railroad in the Centralia/Chehalis area. This may complicate my plans to travel to Portland the holiday weekend.

wxtofly said...

On Sunday, mid-day from about 1:30 -4PM, the uw radar showed two distinct echo spots in what otherwise appeared to be rainshadow from the olympics. One was in the Straight between Port Angeles, Vancouver and Whidbey Is. Another was over the Lummi Pennisula, just West of the North end of Bellingham Bay. Were these an artifact, or were they evidence of a lee wave train off the Olympics?

Jon said...

It's going to be a great week to be a whitewater kayaker.

Jay said...

Hey Cliff, throw us White Pass skiers a bone by including that pass in your predictions, please? 4500 ft at the base.