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gb
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PostSun Nov 24, 2019 7:14 am 
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This is a very detailed synopsis and forecast analysis from the lead forecaster this morning at the NWS. The detail is amazing and shows the difficulty and expertise required to forecast snow in most Puget Sound events:

Quote:
Things begin to noticeably change later tonight into Monday

morning. Exposure to the left exit region of the offshore jet

streak will continue, but a potent vort max will also dive SE

across the eastern Pacific into Oregon overnight tonight. This

will likely enhance shower activity across the area and with

lowering snow levels down towards all pass levels, Cascade snow

accumulation should commence. Although cold air aloft will

continue to infiltrate the region during this time, snow levels

and near surface temps will remain too warm in the lowlands for

snow. This will be a mountain snow event. Should see several

inches of snow across the Passes thru Monday morning, especially

Stevens Pass.



Mid level temps will become even colder thru the day Monday-likely

bottoming out below -30C. Not much will change synoptically thru

the day, with an unstable, unsettled environment continuing. Hi-

res model guidance suggest precip will dwindle into the afternoon

hours as the potent vort max slides south. Snow levels will

continue to plummet thru the day Monday, likely dropping just

under 2000ft by late afternoon. At this time still expecting all

mountain snow and lowland rain showers.



Things could become interesting on a very local scale Monday night

into Tuesday for the lowlands east of Puget Sound. Snow levels

will drop to at least 1000ft if not a bit lower overnight, with

critical thickness values in the 1000-850mb layer near or below

1300m. This indicates cold air above the sfc, but temps at the

sfc will remain above freezing into Tuesday morning, arguing for

mostly a rain (maybe brief snow mix) event. Most light shower

activity over the area will be rain Monday night, tho wet flakes

may mix in at times. The exception to this will be the development

of any convergent zones/boundaries; and several hi-res models are

hinting at the possibility. Given the environment in place, a

convergent zone will have enhanced vertical forcing in place

compared to the showers. These zones will have the ability to

drive snow levels down significantly in very localized areas.Heavy

snow may develop just off the sfc. This can be seen in model

sounding data (esp the NAM) where saturation exists thru the

dendritic growth zone within these bands. If this scenario were to

develop, which it very well could, rain may transition to locally

heavy snowfall in a very narrow band. Heavy snow will likely melt

upon contact with the above-freezing sfc which will act to lower

the sfc air temp. There could end up being very localized snowfall

accumulation that may cause minor impacts if a convergence zone

develops Mon night into Tues. The problem now is that it is

essentially impossible to determine where this would be. Best

guess would be the usual; somewhere between central King Co into

northern Snohomish Co (maybe even into Island Co and southern

Skagit?). This zone could linger into the Tuesday morning commute.

Snow levels Tues morning will be even lower than overnight, so if

any lingering light showers are around, some may be in the form

of light snow showers. No impacts would be expected if this pans

out. Conditions will dry out from north to south Tuesday, with

cold temps expected. Snowfall totals in the Cascades Sun night

thru Tues morning currently in the 8-10 range for Stevens and 4-6

for Snoqualmie.



Kovacik
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dave allyn
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PostSun Nov 24, 2019 7:22 am 
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Can you translate that into English? Seriously though, there is so much that goes into weather forecasting. Considering all the variables the forecasters do remarkably well.
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gb
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PostSun Nov 24, 2019 7:32 am 
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dave allyn wrote:
Can you translate that into English? Seriously though, there is so much that goes into weather forecasting. Considering all the variables the forecasters do remarkably well.

This should help if you have an advanced degree in Meteorology and many years of forecasting experience...... wink.gif


Just kidding, of course, amazing complexity. I've never looked at this from the UW before.
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dave allyn
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PostSun Nov 24, 2019 7:51 am 
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Thank you. It's all very clear now. I just needed the graph.
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ale_capone
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PostSun Nov 24, 2019 8:14 am 
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I'm reading that it going to snow at my house monday night. Better get the plow ready!

It seems we are in a unique spot for weather. Just east of gold bar. All that weather gets bunched up and stuck  like traffic on a Steven's pass traffic on a pow day. Can be observed often on highway 2 around pickle farm. I bet if you put a weather station in town and here, you would have widely differing results.

I think it's because the valley narrows, and air starts going up due to stickney, index, and the merchants. Bending , cuz it's always breezy here. We are still below 200', but slightly higher then town on a rise. We have yet to have a frost event at our house.
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Nancyann
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PostSun Nov 24, 2019 9:47 am 
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Thanks for the heads up gb! Ale, from past experience I agree with your local prediction and will throw in my two cents worth for snow at my house in the foothills above Sultan. agree.gif
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Get Out and Go
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PostTue Nov 26, 2019 8:03 pm 
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From Spokane NWS Discussion:
Quote:
models bullseye Blewett Pass and the Stuart Range with
multiple inches (6 to 12 over a 24 hour period) of snow
accumulation tomorrow and Wednesday night..

Between around the clock snow-making + natural, looks promising for Friday on the White Ribbon of Death at Mission. tongue.gif

And now a 60-70 car pile-up on I-90 near Spokane.  Don't blame the weather; blame the drivers.  shakehead.gif https://www.krem.com/article/traffic/multiple-crashes-snarl-traffic-in-both-directions-on-i-90-near-geiger-blvd/293-36b57920-68a1-413a-b600-71afb4ffc0f8

--------------
"These are the places you will find me hiding'...These are the places I will always go."
(Down in the Valley by The Head and The Heart)
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Cyclopath
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PostWed Nov 27, 2019 9:43 am 
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Blewett Pass is closed!
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cdestroyer
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PostWed Nov 27, 2019 3:36 pm 
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blizzard warning rocky mountain front cold and road closures due to accidents...i90 closed at various points.. check before going
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