Arctic Blast Drops Into Pacific Northwest This Weekend; Unusually Cold Sunday-Tuesday

6:30pm Friday…

Today ALMOST felt like spring west of the Cascades.  For the first time in weeks many of us felt a temperature NEAR normal in the metro area.  See those lower 50s west of the Willamette River and south of Multnomah County?  BTW, the average high at PDX is 54 this time of year.

But also notice the temperature spread even though we all saw sunshine.  44 at the mouth of the Gorge where the cold easterly wind was blowing to 10 degrees warmer well west & south of the Gorge.

Typically, once we reach early March, that cold easterly wind is done for the season and doesn’t return until around Halloween.  Yes, we can get a breezy east wind any time of the year but the “cold” part of it disappears this time of year.  That’s because increasing sun angle allows the Columbia Basin to warm up just as much (or more) as west of the Cascades, lowering pressure there.  That’s the case from early March to late October.  But from November through February those long winter nights and weak sun lead to cold air getting “stuck” east of the Cascades in the Basin.  So the cold easterly wind is a seasonal wind that typically disappears just about now.

But the next 5 days will challenge that assumption.  It’s because we have a very unusual setup.  ALL of eastern Oregon and eastern Washington is covered in a thick layer of snow; which is very rare for early March.

A cold arctic airmass is poised just north of the border this evening

It’ll push south tomorrow, blasting Montana and Wyoming into sub-zero weather again.  As always, the high Rockies will shunt much of that cold air eastward, but this time plenty will surge south between the Cascades and Rockies.  By Sunday afternoon it’ll look like this

Typically this time of year the cold airmass would be passing over bare ground east of the mountains and it would modify quite a bit.  But this time it’ll slide right over snow-covered terrain until it’s within just a few miles of the metro area!  Models show a good 8-10 millibars easterly gradient through the Gorge by Sunday.  The result?  Cold high temps only 25-35 degrees (east to west) Sunday through Wednesday out there.  We’ll see rare March ice on the waterfalls

In the metro area it’ll be very cold for early March with highs just barely making it to 40 degrees in those usual windy spots eastside.  That’s under a sunny sky!

So yes, we have a rare sunny March weekend on the way, but it’ll feel more like January.  High temps will be cooler tomorrow, with most of us staying under 50 degrees.  Then a good 5+ degree drop Sunday keeps all of us in the 40s with areas near the Gorge (Camas/Troutdale/Gresham) remaining in the 30s.  Brrrr!

Of course I checked to see if we might break some records.  We might, but Portland’s “record-low” high temperatures from Sunday-Tuesday are 29, 34, 36.  We aren’t going to be that cold.  Two of those days were during a very late season snowstorm.  Record lows for those three days are 19, 26, 19.  We could break that middle record Monday, but only if easterly wind dies down at the airport; unlikely to happen.

I think it’s more likely we’ll see some record lows in some of the calm areas Monday-Wednesday mornings, assuming skies remain clear.

Here are the final snow numbers for February from PDX.  Tomorrow or Sunday (I’m working this weekend), maybe I’ll do a February snow totals post.

 

Chief Meteorologist Mark Nelsen

Welcome to Spring! Sort of…

8:30am Friday…

I got up early today since I had last night off.  Woke up to maybe 1/2″ fresh snow on the ground but glorious sunshine plus some blue sky.  It’s beautiful, but after having the ground mainly white for 3+ weeks, I’m ready to move on; it’s March 1st.

That means we have crossed into spring.  That’s meteorological spring, which north of the equator is March-April-May.  The sun is already as strong as it was in early October when the average high temp is in the upper 60s.  It always drives me nuts when I hear someone say the “official” start to spring, or any other season.  It’s okay to say “traditional” start to spring (around March 21st) since our calendars say that and it sure is tradition.  But as far as I’m aware, the only spring the U.S. government officially recognizes comes from NOAA and that’s March through May.  That’s my Friday morning rant.

The next few days will NOT feel like spring (except for the strong sun hitting your face!).  A modified arctic airmass will be descending on the Pacific Northwest later Saturday through early next week, challenging some cold weather records.  I’ll take a closer look at that on a posting when I get to work this afternoon.

Plan on lots of sunshine, but a cold east wind much of the time this first week of March.

Chief Meteorologist Mark Nelsen