Finally, Heavy Snow Moving In

March 12, 2012

All or ODOT cams along I-205 show heavy snow, starting to stick in Oregon City area too.  The rest of us should changeover soon.


Did You Ever Think You’d See This?

March 12, 2012

Sea level at Lincoln City, snowing heavily with at least 1-2″ on the ground:

4,000′ at Government Camp, raining with wet pavement at the same time:

What’s wrong with this picture???  There is a cold front (leading edge of cooler air) sitting across the Willamette Valley.  In the warmer air ahead of the front, sticking snow level is up around 4,500′.  In the colder air behind the front, steady and heavy precipitation has been dragging the snow level all the way down to sea level.  Perfectly reasonable, but I’ve never seen it before!

Previous snow forecast from posts below still applies;   we should changover to snow in the next couple of hours as the front resumes it’s eastward move.

Chief Meteorologist Mark Nelsen


3:45pm: Wind Winding Down & Snow Update

March 12, 2012

Looks like the wind is off it’s peak in most spots, it’s most obvious by the PGE outage count, down around 5,000 after about 14,000 earlier.  Salem didn’t make it on this part of the map, they hit 56 at the airport, the highest of the wet season.  Same with the 48 at PDX.  In fact it’s been quite a pitiful south wind season for the valleys.

Now it’s on to the snow…we’ll see how it goes.  Our 18z RPM isn’t backing off at all, showing a wide swath of 1-2″ in many areas of the Valley:

 

The 12z 1.3km UW-WRF is out.  Of course the Huskies have the only 4 year meteorology program in the Pacific Northwest AND the highest resolution model available for our area.  Look at the detail!  At this resolution you clearly see the West Hills, Bald Peak, volcanic highlands of eastern Multnomah/Clackamas Counties, etc…  All those areas get 2″ or more tonight.  Note that the higher resolution is also better at picking out NO SNOW areas.  Not everyone is going to see sticking snow.  Lowest elevations around Hillsboro, North Portland, St. Helens, Woodland and spots in the Valley may see nothing…thus the ZERO to 1″ forecast in the lowest spots.


Unusual Late Winter/Early Spring Snow For Many Tonight

March 12, 2012

10:30am: We’re about 2 hours into a fun 24 hours of weather folks!

For those looking just for details, here you go:

WIND:  South wind gusts 40-50 mph possible anywhere from Vancouver to Eugene the next 3-4 hours, so far they have been mainly south and west of Portland, but it’ll get stronger for the rest of us after noon.  They calm quite a bit after 2-3pm.

SNOW:  Most or all of us will at least see snow in the air sometime between 8pm and 8am tonight and tomorrow morning.  It shouldn’t affect the morning commute at the lowest elevations, but a mucky, slushy mess up around 1,000′ and above.

Lowest elevations Longview-Vancouver, Portland, Salem, Albany: 
Zero to 1″ possible between 10pm-5am

Around 1,000′: 
2-3″ possible anytime after 9pm-8am.

Around 1,000′ east of I-5 in the Cascade Foothills (Sandy, Detroit, Mill City etc..):
2-5″ during the same time period.

1,500′-2,000′:
6-10″ of heavy, wet snow

Keep in mind, as always, that elevation distinctions are approximate.  We just can’t forecast in 200′ increments; that’s only a difference of about 1 degree at best.  But there’s nothing wrong with averaging between the numbers, for example for someone at 500′ I’d say a really good chance of SOME sticking snow, but somewhere between a trace and 3″, heaviest likely out against the Cascades (like Corbett or Boring).

FOR THE WEATHER GEEKS…SOME DISCUSSION:

Strong southerly wind has surfaced the last few hours through the Willamette Valley and west side of the Portland Metro area.  Gusts 40-50 mph have been spotted over there.  I see a 51 mph at Forest Grove.  The eastside and most of Clark County are protected from the strong wind so far by the easterly wind flowing out of the Columbia River Gorge.  Think of the Valley as an interstate freeway with traffic flowing north this morning (south wind), but cars are merging onto the freeway (coming out of the Gorge on the right) and slowing down the right hand lane.  Hopefully that makes sense.  During the big 2007 Coastal Gale it was similar with strong wind all day west and south metro but much lighter conditions eastside and Clark County.  By noon or so the east wind backs off, so that will be the windiest time of the day across the eastside.  The wind in all areas backs off to almost calm after 2-3pm as a cold front passes through…then a bit more fun…

Everything still looks set for a heavy wet snowfall in the hills tonight, and anyone that is awake at even the lowest elevations from Vancouver to Eugene is at least going to SEE snow in the air as soon as 8pm tonight through about 8am tomorrow.  You can see the previous post for details, but models have still not backed off on a the perfect combination of:

1. Steady precipitation from around 8pm-2am or a little beyond

2. Much colder temperatures above…about -5 at 850mb

3. Calm or nearly calm wind

4. Leads to a nearly isothermal atmosphere…around 32-34 degrees from 2,000′ all the way down to the surface.  Look at the sounding for 2am tonight over Portland as an example:
ALL mesoscale models continue in quite good agreement on at least SOME snow even on the lowest hills, and probably a dusting everywhere.

Here is our RPM, which keeps showing 2″ plus just about anywhere EAST of I-5.  The reason for that is heavier precipitation for a longer period of time as the westerly flow runs into the Cascade foothills.  This is common in this pattern.  When I think of post-frontal, heavy snowfall events I’ve seen like this in the past, it’s almost always an eastside and hills event:

And the highest resolution model we have right now, the 12z WRF-GFS.  Note the 2″ plus areas on hills such as Bald Mtn, highlands around Oregon City, Powell Butte, Mt. Scott and the West Hills of course:

Chief Meteorologist Mark Nelsen