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6pm Thursday...

I figure I better get ahead of this one!  That's before somebody tweets/retweets a picture like the one below, then everyone shares it to their friends on Facebook, followed by a news organization and public official calling for the Storm of the Century...  It would be followed by a serious run on milk, bread, & kale.   Not good.

Capture

As you can see, at one point two days ahead of Super Bowl Sunday 2017 our models were showing a fantastically historic snowstorm over NW Oregon and SW Washington.  But as we got closer to the event it became obvious the big snowstorm would be NORTH of the metro area.  As I recall Chehalis had a huge 16" of snow in one night!  We had a pouring wet 34 degree rain all that afternoon and evening...so close.

THAT is one reason why I don't forecast detailed snow forecasts more than 1-2 days ahead of time, unless all models are in great agreement.

A QUICK SUMMARY OF WHAT I KNOW AT THIS POINT

Nothing interesting happens between now and Sunday night, just a wet weather system Friday afternoon, then chilly showers (snow in the foothills again) Saturday and Sunday

  1. Monday through Tuesday (or possibly Wednesday), a strong and cold east wind will pour out of the Columbia River Gorge and into metro area plus north Willamette Valley.  That's because another surge of cold arctic air moves down into Eastern Washington during that time...brrr!
  2. EACH MODEL IS DIFFERENT, but at least 2 of the 3 main global models produce some sort of lowland snow by Monday morning, possibly through Monday/Tuesday (depending on model) in the Gorge and through the Portland/Vancouver metro area.  Others say no, all the moisture stays south and we get nothing.
  3. This could easily turn into nothing as we get fresh info the next 48 hours.  But I just want you to be aware that SOMETHING "snow-wise" COULD affect your life at some point between Monday and Wednesday.  DO NOT change any of your plans/activities or rush to the store at this point.  Don't y'all have enough food to last another two weeks anyway?

TECHNICAL TALK

Through February 20th, this is the third coldest February on record here and the coldest in 30 years.  That's because THIS pattern keeps occurring in the upper-atmosphere

500_now

I drew in the flow at around 18,000'.  The entire West Coast is cold.  It snowed in Las Vegas again and a Freeze Watch is up for part of the L.A. area tonight.  You can see another wiggle in the jet stream coming out of Alaska.  That moves down to SW Canada over the weekend and settles in.  But there is a change head.  A strong upper-level ridge builds over Alaska this weekend, allowing a cold surge of air to move south.  By Sunday it looks like this.

500_Sunday

The problem comes right after that.  Here's Tuesday

500_Tuesday

A milder jet stream from the west tries to punch in over us at the same time the cold northerly flow is overhead.  The combo of these two is quite difficult for models to resolve.  A slight northward movement of this pattern means we get plain old rain.  Too far south and we're dry plus cold.  The "sweet spot", if you want one last snow event in Portland, is what some models are showing for Monday/Tuesday.

All models are showing this general setup for early next week, but it's that slight north/south movement that matters.

One thing is certain, in the last few days of February it's ALMOST impossible to get a day-long crippling snow or freezing rain event in the metro area.  That's due to increasingly strong sunshine (getting higher in the sky).  Right now we are getting as much energy from the sun midday as we see the 2nd half of October.  To bring the entire metro area to a halt for a whole day, it would need to be steady & heavy snowfall from near sunrise to mid-afternoon.  It's possible, but everything has to be just right (or wrong).  Also, I've never seen a metro-wide all-day freezing rain event this late in the season either, it's even more difficult to keep a dark road surface frozen under clear ice in late February.

I may not be able to post Friday, busy with a few personal things and then I'll be up in the Cascades later in the day for a work project.

Chief Meteorologist Mark Nelsen

Chief meteorologist

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