Cold Air Arrives Monday

December 28, 2014

Just 3 days!  In the entire month of December we’ve only seen 3 days with temperatures below normal…all at the beginning of the month.  Since that time it has been very mild.  In fact no freezing here in Portland for over 3 weeks!

MarkTemp_Last12Days_LowsPDX

Tonight we’ll stay mild with temps above freezing and just a few scattered (rain) showers.  Then cold air starts pouring into the Pacific Northwest as skies clear out tomorrow.  I haven’t been expecting any snow below about 1,500′ west of the Cascades because we dry out at the same time the cold air arrives.  That doesn’t mean you couldn’t see snowflakes mixed in with early morning showers, but that’s unlikely too.

The intensity of the cold air looks about the same as mentioned in the previous post.  This is not a “mega” blast of either east wind or cold air that we COULD see this time of the year.  High temperatures in the low-mid 30s under sunny skies are sure chilly, but nothing like 20s!  As for east wind, just the usual gusty easterlies tomorrow and Tuesday, then mainly calm Wednesday/Thursday.  Models only suggest 4-6 millibars easterly gradient through the Gorge, much tamer than the Veterans Day east wind event.  In fact check out the current WRF-GFS cross section:  kpdx.th

vs. the November version…that was a wild forecast and it verified!  kpdx-th1

With calming wind and a cold/dry airmass, we could see the coldest temperatures so far this season either Wednesday or Thursday morning.  23 is the coldest temperature we’ve seen so far in Portland.

Beyond that, models have gone back to a ridging/split flow setup along the West Coast again for next weekend and beyond.  So it’s especially good that we’ve seen some great snow totals this weekend in the Cascades.  What an improvement in just 7-8 days!

MarkSnow_MtHoodTotals2

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Chief Meteorologist Mark Nelsen