Thursday, January 22, 2009

Cold, but no snow in Seattle

I have been studying the latest computer forecasts and it is clear that this weekend will bring major changes....but no snow in Seattle.

Starting with today, low clouds and the inversion are still in place over Puget Sound and eastern Washington (see satellite picture and the latest profiler temperatures in Seattle). The inversion is a weaker than last week on the west side...and some locations are seeing some sun midday. But the clouds fill back in overnight. And tomorrow won't be very different.
I have added a figure showing temperatures over the past four weeks against the average highs and lows (red and blue lines). During the last week we have been much cooler than normal..which comes as no surprise. The spike of really warm temperature two weeks ago was the pineapple express flooding period.
Now to the forecast. An intense high, associated with very cold air, will form over the Yukon and N. British Columbia and move southward towards our region. By tomorrow morning at 4 am, a 1054 mb high will be over northern BC. (see figure), and cool air will begin seeping into northern Washington. By saturday cool air will be moving SE in the Fraser River Valley and NE winds will be hitting Bellingham and NW Washington (see figure). Colder air will move southward on Sunday, but right now the models indicate very little precipitation....so no snow. Moderated arctic air will move over western Washington and we will probably clear out on Sunday. With dry conditions and offshore flow the strong inversion and fog that we have experienced should be history.

16 comments:

Anonymous said...

But snow in Olympia?

Anonymous said...

I have a question about the satellite photograph - the first image in your latest blog post. There is a large band of clouds that goes east west across washington. On the northern edge of that band is a narrow dark band - is that the sun's shadow? And is that band of clouds really high up, like how high up? I'm curious to know how many feet in altitude that shadow band is representing - if that is a band of shadow.

Cliff Mass Weather Blog said...

Probably no snow in Olympia either..but the chances improve to the south.

That upper is a band of higher level clouds--probably 10-20 thousand ft up. And you are quite right...that is a shadow...

andycottle said...

To answer that question....yes, the sun is casting a 'cloud shadow' down below. Much like you see on the first and last visible satellite images of the day.

Those clouds appear to be of the alto-stratus/ alto-cumulus type, and those clouds are roughly 14k to 20k in height. So the shadow you see is likely being casted from those heights.

cloud shadow questioner said...

Thanks guys - I'm learning so much

Anonymous said...

What sort of chances for snow to the south? I have to drive to PDX late Saturday afternoon to pick up my son, who's been overseas for 6 months.

Should I be afraid?

P.S. Thanks for this blog. It is a voice of reason and intellect in a media weather-world run amok.

cloud shadow questioner said...

As long as you guys are around, can you tell me, the photo on the post says 2300 UTC - what time is that here? thanks again

Cliff Mass Weather Blog said...

2300 UTC is the same as 2300 Z or GMT which is 3 PM PST...

andycottle said...

Think 2300 UTC time would be 11pm here because 12am would be 0:00 UTC..

andycottle said...

EDIT: Looks like I may have been wrong on my answer..

climo man said...

Looks to me like a minor "back door", arctic outflow episode coming up.It`s hard to get very excited about it when then 500MB heights are not expected to fall below 540.( The upper high is still not far enough offshore to facilitate a strong flow of arctic air.) Maybe we`ll get "lucky"( at least in the snow-lovers` opinion), and a surface feature will spin up further north than where currently is being forecast, and we`ll get something(white) to really talk about.I`d also like to point out that almost exactly one year ago, Jan 20-23 2008, we had virtually the same weather pattern that is expected to occur this weekend.(A very positively tilted ridge; clear with max temps in the 30`s to low 40`s, and min. temps in the 20`s.)

andycottle said...

Hey I got a question for all of ya and even Cliff can chime in...

With this trough coming down over us, isn`t there also a weak low pressure that comes in just south of us to throw up some moisture over the colder air? Seems like GFS was kinda showing that..

Mike the pilot said...

Subtract 8 hours from GMT to get PST.
Subtract 7 hours from GMT to get PDT.

In other words, 0000z is 4pm Seattle time in winter, 5pm in summer.

(I'm also driving or flying SEA-PDX on Saturday and eager to hear about snow)

Anonymous said...

I'm driving to Salem and back this weekend so will have to watch

climo man said...

andycottle:
A trough or surface disturbance is predicted to develop off the Southern Oregon coast, which normally is too far south to give snow ( under favorable circumstnces) to the Seattle Metro Area. That is why the highest probability of snow is currently south of Seattle.Lately,each progressive model seems to have been weakening the disturbance or projecting it further south.Just check the satellite images or weather maps late Saturday to see if and where the predicted trough develops.Location is everything! I think everyone knows now that probably the best locaton for low pressure to develop and combine with an artic outflow to cause snow in the Seattle Area is just off the mouth of the Columbia River.(Especially true if the low tracks east, not north.)

andycottle said...

climo-man....please just call me Andy. :o)

Yeah, as the t.v ad says....location, location, location! lol.