Updated Snow Outlook For This Weekend

February 24, 2012

The main weather story continues to be the possibility of lower elevation snow at times Saturday through Tuesday. This is another one of those situations where we don’t have a cold east wind blowing out of the Gorge or a cold air mass to give us a widespread snowstorm.  Instead we just get showers and clearing periods Saturday and Sunday and it happens to be a colder version of the “showers and sunbreaks” pattern. 

In general, the higher up you live the better chance you have for sticking snow.  All areas dry out Sunday evening and that’ll be the end of it until Tuesday.

First the outlook for regular folks, then the in depth model & data discussions for my “weather friends” down below.

IN THE LOWEST ELEVATIONS ALONG I-5 HERE IN THE VALLEY:  This includes Salem, Portland Metro Area, Vancouver, St. Helens, & Longview.  Mainly rain showers during the day Saturday, then mixed rain/snow showers Saturday night through Sunday afternoon.  If we get a dusting of snow, it would likely be early Sunday morning, but only some random neighborhoods will get that dusting.  Most of us in the lowest elevations will get nothing better than snowflakes in the air this weekend.

NEAR AND ABOVE 1,000′:  This includes the West Hills, Mt. Scott, Sandy, West Salem Hills, etc.  This also applies to areas from 500′ on up in the Coast Range like Vernonia, Elsie, & Timber.  Snow showers Saturday morning through Sunday afternoon could give light accumulations, especially during the cooler nighttime hours…1-3″ possible in these areas.

NEAR AND ABOVE 1,500′:  This includes Coast Range summits, Hoodland area, Silver Falls, Detroit Lake...Snow showers late tonight through Sunday afternoon; 5-8″ is possible during this time, heaviest up against the Cascades.  Snow could accumulate at any time on roads, but snowiest during nighttime/morning hours.

CASCADES ABOVE 2,000′:  18-24″ by Sunday morning, maybe another 6″ during the day Sunday too.

 

TECHNICAL DETAILS:

Starting tonight, we’re going to see snow levels below 2,000′ for the next 5 Days.

Nice strong cold front just about to the Coast right at 5pm.  What a brief taste of spring this morning with bright sunshine and temps quickly zooming up into the low to mid 50s across the metro area before the clouds moved in.  East of the Cascades, lots of 60s with southerly wind surfacing all over the place.  But forget about spring and check out the cold cumulus behind the cold front.  Just 12 hours it didn’t look so great, but now you see the northwesterly flow setting up behind the front with the usual showers streaming towards us.

Models show the deep surface low near Vancouver Island moving by to our north over the next 12-24 hours; WRF-GFS gives us 13+ millibars EUG-OLM gradient by midnight or so, which could give us 40 mph wind gusts.  It’s going to be a showery & windy night! 

A steady stream of showers tomorrow, with 850mb temps between -6 and -7 degrees means snow sticks even during the day up around 1,500′, but the strong onshore flow and sunshine in between showers means no “stickage” down here in the lowlands.

Cooler air, by just a couple of degrees, for Saturday night and Sunday means a better chance for sticking snow slightly lower, but moisture seems to run out after midday Sunday.  So that’s why I think the best window for a dusting down in the lower elevations is later Saturday night through 10am Sunday.  Still, I’m not real impressed by what I am seeing.  To me this appears to be a slightly lower chance for sticking snow here in the city than what we saw that weekend in January; we didn’t officially have snow during that episode in Portland.  I’m not referring to the following Tuesday night when we had several inches.  Our RPM looked better at that time than what it shows now:  just a sprinkling of snow in some spots in the valleys:

Here is the 12z 1.3km WRF-GFS snowfall graphic…that’s some geographic detail at that resolution!

There is one possible wrinkle, models have been slightly stronger with a disturbance coming down the coastline around midday Sunday that could enhance the showers.  Hopefully if that occurs it WILL be midday and not give us anything significant.

Sunday night and Monday we dry out, so Monday should be a real nice, but chilly day with 850mb temps remaining in the -6 to -8 range…brrr!  Even so, late February sunshine should get us close to 45.

Tuesday is a challenge as a cold front moves through the Pacific Northwest.  
1.  We start with a chilly air mass
2. Precipitation rushes in during the morning hours
3. Little to no southerly gradient until midday, in fact light easterly flow early in the day.
4. 850mb temps TOP OUT at about -3, with -6 degree temps ahead of and behind the front.

This could be a good snow producer at/above 1,500′ with snow in the air everywhere to start; at least it’s something to keep an eye on.

After leftover showers Wednesday (similar to Saturday’s weather), we finally see some warmer weather showing up on both the GFS and ECMWF.  Not WARM, in fact barely mild, but at least near normal March weather; we could see a bunch of 50s instead of low-mid 40s possibly?  How exciting!

Here are the 12z GFS and ECMWF 850mb charts showing the possibility of milder weather:

 Chief Meteorologist Mark Nelsen