Monday, December 15, 2008

More snow

This morning the low center and associated clouds/snow has moved south of us...with snow still falling over Oregon (see image). Low temps last night dropped into the low 20s in Seattle and in the teens in the cooler hinterlands. If you think this is cold...head to the upper plains where low records have been broken (such as the -15F at Denver). As noted in earlier blogs, this cold will be around for a while. But first lets talk snow.

An upper level disturbance...known as an upper level short wave trough in the business...will move southward out of Alaska and BC late Tuesday and Wednesday morning (see upper level map). This is close to the canonical situation for NW snow. Right now it looks like snow will begin falling over our area early Wed morning (perhaps very late Tuesday) into early Wed afternoon. As this point, it looks like amounts will be modest, roughly 1-4 inches, with some scattered higher amounts. To get really major snow we need a low developing off of the SW Washington coast and this is not being predicted (see map). The reason this is such a favorable pattern is that the low draws cold air in the from the north, while rotating Pacific moisture up and over it. But at this point, the low is too far inland for such heavy snow. So be ready for a modest snow event.

But the real threat is on Sunday. A far stronger weather system is forecast to approach the area...and with cold air in place we could have a major snow event that would make Wednesday look small. But this far out this is still a lot of uncertainty.... But if you need to buy car chains...I would do it.

15 comments:

Jim said...

Cliff, will Sunday's snow represent a transition to a warmer regime or will be back into the icebox in your estimation?

Matt said...

Another Sunday question... so is driving to Spokane looking to be a bad idea?

Cliff Mass Weather Blog said...

Today's model output suggests we might stay cold...but we would be on the edge. If the mega event occurs on Sunday, driving anywhere would be a bad idea. But never get excited about snowstorm that is more than 4 days out! There are only a few ways we get serious snow in Seattle and a million ways for it to go wrong.

Joseph Ratliff said...

Cliff,

What classifies as a "major" snow event around here? I can remember living in Everett in '96 or so...and getting like a foot + .

Is that the type of possible even happening Sunday? A dumping? LOL...

Olivier said...

Looks like Wednesday's storm, has strong NW winds, which could create a rainshadow over central and southern seattle area. MM5 3 hour precip totals dont look to impressive for that area. Hopefully as the low drifts south, the SW winds will bring snow to that area also.

Cliff Mass Weather Blog said...

Olivier,
You are right...there is the potential for substantial "snowshadowing" of Puget Sound by the Olympics. But NW flow can also bring the Puget Sound convergence zone..which has brought substantial snow in some cases (e.g., Dec 18, 1990)....so not an easy forecast....cliff

Anonymous said...

forget about last winter and this one, you global warming types are going to just LOVE what the PDO has in store for you in the coming winters. factor in the lack of sunspots and the CO2 types should be looking to hide right now !

Anonymous said...

For the other anon. poster--I'm not sure that it makes a lot of sense to imply that a negative PDO and the sunspot cycle are going to produce harsh winters. To me, it doesn't make any more sense than, say, last month to attribute the mild November (4 degrees F above normal in Seattle!) to global warming. In the short term, it all seems to regress to the mean. Mild month, cold month. Snowy winters followed by low snow cover. The swings we see from month to month and year to year are large--certainly much larger than the incremental long term trend that you might try to assign to a given month or year.

To me it would be interesting to know how these week to week and month to month changes come about. How is it that the ridging along the west coast in November suddenly dissipates, or maybe retrogrades to a different position. What a swing to go from such mild weather a couple weeks ago to this Canadian air mass.

Anonymous said...

there is considerable science to support that the major weather driver for the PNW is the PDO, there is also considerable science to show that earths energy received is a function of spots or lack thereof on the sun.

the temp / precip / cloud cover in Bellingham vs Seattle is fluff, right now its cold - period.

to say that your unsure about these having effect, says to me that you have only a superficial understanding of both.

Anonymous said...

My understanding of climatology is not the point--I'm not a climatologist!

If a climatologist said that a negative PDO and the recent sunspot minimum forces a climate model to give Seattle fierce winters, I'd say bring it on! But your message that
"CO2 types should be looking to hide right now" isn't very authoritative. And neither are my questions about short term weather/long term climate. I was merely trying to have a conversation--no need for insults. I never claimed to be anything but curious and anonymous. If you're a published academic climatologist you should start up your own blog, I'd read that!

Anonymous said...

To the questioning non-climatologist:
Thank You! It was getting a little windy in here...

Anonymous said...

Seriously, guys? You're trolling the weather blog of a UW professor who gets maybe 100 hits a day? You really don't have anything better to do?

a progressive crank said...

Professor Mass, if you have to respond to the trolls who think they know more about meteorology than you do, make sure you bury them. Don't think for a moment they will be receptive to a gentle reproof. Obviously, they have no credentials (or why sign off as "anonymous"?).

I agree with your late mentor that we need more popularizers of science who can bring the facts into the public square. Good for you for doing it.

natchrl8r said...

I very much appreciate what Cliff is doing in popularizing interest in weather and climatology. I am one of those common "weather buffs" seeking a little more knowledge and understanding of the weather phenomena we experience. What I object to is inflated amateurs using this as a forum to show off or pummel each other and ridicule the legitimate questions of us buffs. Lighten up! By all means share your knowledge and opinions with us and remember we are here to make it fun and interesting.

Anonymous said...

Thanks! I was surprised I'd been called a troll and also scolded by John McBride. I just commented that things in the short term regress to the mean. But maybe our pattern change these past few weeks resulted from progression of the Madden-Julian oscillation? Just questions. I am very sorry there was such a bit of an uproar.