A “Classic” November Day Monday: Then Coldest So Far This Season

November 17, 2013

Tomorrow looks like a soaker, especially the second part of the day as a vigorous Pacific frontal system arrives.  Rain should pick up in the 2nd half of the day at the same time a surface low pressure center tracks from off the Oregon Coast to around Seattle.  That gives us gusty southerly wind the 2nd half of the day and through the evening.  Gusts should reach around 55 mph on the Coast and 30-40 mph here in the valleys.  Not a big wind or rain storm, but just enough of each to make for a miserable evening commute whether you are in a car or not.  Note the relatively light precipitation totals (no flooding) for the next 48 hours:

RPM_12KM_Precip_NWOR

The bad news for skiers is that we’re going to see 1-2″ of mainly rain at all the ski resorts (snow above 6,000′ only) tomorrow afternoon through early Tuesday.   Not good.

This is the only rainy weather system we see for at least the next week!  What’s going on?  A ridge of high pressure in the atmosphere is going to take hold across the Pacific Northwest.   This one will be a bit different from the last in three ways.

1. Unusually dry air from the north comes in quickly behind the cold front Tuesday morning.  So the rain will just stop, and then we’ll see dewpoints plummet to the lowest values we’ve seen since last winter.  That’s the measure of moisture in the air.  Models are saying 15-25 degree dewpoints.   As a result, we’ll see lots of sun starting Wednesday.

2.  With the much drier air, fog should disappear in all areas west of the Cascades from Salem north through at least Friday-Saturday.

3.  Coolest airmass so far this year settles east of the Cascades, and now it’s inversion season so it won’t go anywhere.  Cool air will be spilling out of the Gorge.  Highs in the mid-upper 40s west of the Cascades with a dry airmass says 20-25 degree lows later in the week in the colder spots (Hillsboro, Orchards, Vernonia etc…).

The low temps I put on the 7 Day forecast this evening are meant to be representative of the entire metro area, not PDX where the wind will be blowing the 2nd half of the week.  In windy areas it’ll barely get below freezing:

7 Day

 

What won’t be different with this ridging?  That gorge wind will start blowing some on Wednesday, then really ramp up towards the weekend.  We’ve seen that this fall already.  Although this time we’ll get very warm temps aloft along with the cooler air below; a good setup for a very strong gorge wind event Thursday through ????.

As I mentioned on Friday’s post, looks like ridging is going to want to stick around.  Both the ECMWF and GFS are keeping things quiet weatherwise to at least the last few days of November.

Chief Meteorologist Mark Nelsen