Ice Storm or No Big Deal?

November 28, 2006

Chilly evening in progress out there with clear spots already in the mid 20’s.  Cold & dry air finally pouring through the Gorge this evening too with dropping dewpoints at Troutdale with a light east wind.  I’m a bit concerned about the low clouds lingering around the metro area at 10pm, but I’m assuming the drier air moving in from the east will evaporate that in the next few hours.  Otherwise low temp forecasts will be in jeopardy.
Now as for tomorrow night’s system…some common themes from 00z mesoscale models.
1.  Precip on all models begins around midnight.
2.  Strong gorge outflow never really develops, probably because the system is approaching from the northwest.  It’s those lows coming up from the southwest that really suck out the cold air and wind.  I wouldn’t be surprised if we dont’ see 8 millibars from DLS-PDX.  In each of our last 3 ice storms that gradient exceeded 12 millibars.
3.  Low pressure tracking by to the north is also very unlike the last 3 ice/snow storms.  This pattern produces a gusty south wind west of the Cascades and kills eastside high pressur quickly too.

This all adds up (in my mind) to a very brief freezing rain event.  I’m amazed how quickly the MM5 and our RPM model warm things up, much faster than they did with the last few storms.  I believe it with this pattern.  Temps tomorrow night may only briefly touch 32 degrees as a result and then quickly jump to 40 by daybreak in most of the metro area.  In fact wind turns westerly in the Gorge (or at least calm) by 10am Thursday!
Snow is unlikely because there is just too much warm air above from what I see, of course a few flakes are possible at first, but that shouldn’t last long.

11pm Extra:   After looking at 00z Canadian, 00z GFS, 00z ECMWF I took the rain out of the 7 Day forecast.  It’ll show up within the hour online…looks like a long term ridge coming up.    But, there may be a silver lining.  Just like last year in early December, chilly air will probably get trapped below the ridge east of the Cascades, especially since there won’t be much chance to melt the snow cover over about half of the Columbia Basin right now.  So I lowered high temps for early next week too…Mark


Cool Afternoon

November 28, 2006

A brief post for now, then more detail on tomorrow night’s system later when I have more time.

As expected, arctic front has just turned into more of a "northerly drift" across the metro area.  At 2pm temps range from 32 up at Kelso to 40 or so down towards Aurora/Salem.  Visible satellite picture shows the edge of the northerly breezes moving down into the Willamette Valley.  And it really is a "drift", very little movement out there.  But mesoscale models never showed a good push from the north.  What they do continue to show though is a good easterly gradient developing through the Gorge overnight.  Of course as that begins we have calm winds here in the metro area for a very cold night, then the Gorge wind spreads across the city tomorrow.  35 seems like a good high since The Dalles should stay around 28.  I am impressed by how cold that arctic airmass was.  12 at Bellingham with the northeast wind raging this morning, and widespread dewpoints below zero in north central Washingotn.  Too bad it isn’t like previous ice storms where that cold air really gets sucked down through the Gorge.  On that note…I have lots of thoughts about tomorrow night, but it’s off to a news meeting because all the newsies want to know the scoop…Mark