Weekend Extra: Snow/Ice Update

January 9, 2011

I just spent over an hour staring at maps, models, satellite, and even maps from old ice storms here in the Metro Area.  Yes, I actually save old maps just in case a similar scenario occurs in the future.

I’ve become aware the last month that the link to Twitter and Facebook (fox12weather) is bringing a lot of “normal” viewers and users over to our blog.  By NORMAL, I mean anyone that doesn’t stare at weather computer models all day.  Of course I don’t fit into that group.  So if you have no interest in that, skip to the bottom of the page for my snow/ice outlook:

For the rest of us:  what a mess the past 4 days trying to figure out what is going to happen this week!  I didn’t want to get into model riding (the ups and downs), so I only checked in every 3-4 runs.  Things seem to have settled down now with all models showing surface low heading north of us Wednesday.  A very juicy warm front swings through Tuesday evening/Wednesday AM with the low, making for a relatively quick weather event.

I think almost all of us from Tillamook north along the Coast and Albany north in the Valleys will see SOME snow later Tuesday.  But I don’t think ANYONE has a chance of seeing snow much past midnight Tuesday night here in the Western Valleys; far too much warm air surging in overhead.  So the tricky part is figuring who gets how much snow.  You see my thoughts down below.  It’s obvious to me that’ll we’ll have a significant period of freezing rain here in the Portland Metro area through the night and into Wednesday AM.  I could see 1/2″ of ice here in town on top of the snow for several reasons:

1.  Even the mesoscale models don’t show a southerly gradient (at the surface) in the Portland Metro area until around daybreak. 

2. I’m assuming they are a bit fast getting rid of the easterly flow too, so I say no temps above freezing in the bulk of metro until 7am Wednesday.  After that it COULD go quickly (the warm up) due to the nice southerly wind up the Valley.

3.  Previous ice storms.  I just took a close look at January 15, 2005.  I still have the MM5-GFS maps.  Similar setup with warm southwest jet punching in; no big “surge” of cold air in from the north (although colder than what’s coming for Tuesday), but surface low pressure pulled the cold air through the Gorge.  At the end of the event the MM5-GFS had shown gradients going flat in the Gorge and several millibars southerly gradient in the Valley.  Instead it was still gusting to 30 mph at TTD and PDX was barely above freezing.  So if models are a bit off, freezing rain could easily continue near the Gorge through part/all of Wednesday.  I sure don’t believe Hood River or The Dalles will climb to freezing Wednesday.  A 2nd surge of moisture Wednesday night could mean a major ice storm in the Gorge then (1-2″ ice accumulation around Stevenson/Cascade Locks).

So no epic snow or ice storm here in the Metro area as it appeared several days ago.  The worst case scenario (for us weather weenies) is 2-3″ snow, freezing rain all night, then suddenly 40s after daybreak.  History says that’s unlikely, that’s why I didn’t go with it.  But this is better than nothing right?

Now I have no reason to doubt the warm southerly surge up the Valley at the surface later Wednesday through Thursday, so it’s going to be quite a change…into the 50s Thursday.

OUTLOOK:

Snow begins falling in the Willamette Valley later Tuesday afternoon (timing uncertain), then picks up quickly around commute time and beyond.  Could even be heavy for awhile.  A quick changeover to rain at Salem (hopefully no freezing rain) after just a couple inches or so.  But here in the Metro area it’ll probably be all snow for a good 6 hours or more.  So we MAY see 3-5″ snow before a changeover to freezing rain in the middle of the night.  By daybreak Wednesday, temperatures probably still right around freezing (or below) still in Metro area.  That means I expect an icy mess; snow covered by a thick glaze of ice from freezing rain for whatever little Wednesday AM Commute there is.

Then a rapid warmup for almost the entire metro area as Wednesday proceeds…end of storm.

In the Gorge…the worst snow/ice event we’ve seen in two years.  A good 10-15″ snow from Bonneville East, maybe 4-6″ west end (Corbett area) before a changeover to freezing rain.  Quite an ice storm then continues central/eastern Gorge through Thursday morning, possibly longer.  West end may go above freezing later Wednesday (maybe).  I’d avoid I-84 Tuesday PM through Thursday AM.

Chief Meteorologist Mark Nelsen