A Colder 7 Day Forecast

January 31, 2014

You’ve probably noticed our 7 Day forecast is much colder than 48 hours ago.  That’s because a cold airmass will gradually work south out of Canada Monday through Wednesday of next week.  There is no “storm” or “system” coming.  It’s just an increased flow of cold and dry arctic air.  For that matter it’s not a polar vortex either; in case you were wondering.

If you are looking for the highlights of the next week, here you go:

1. Mainly dry this weekend, a sprinkle is possible on Sunday

2. A few showers of either rain or snow are possible between Sunday night and Monday night.  At this point it appears there may not be much of anything, so most of us will likely stay dry.  I don’t see a good setup for a decent snowfall in the lowlands west of the Cascades.

3. Cold east wind starts blowing late Monday and reaches a peak Thursday or so.  This will be the coldest and strongest east wind (the two together) we’ve seen all winter.

4. We’re talking high temps around 30 or even colder in Portland, and 20-25 in the Gorge!  Not quite as cold as December’s arctic blast, but close.

5. Mostly or all sunny skies Tuesday through Friday next week

 

Take a look at the 500mb chart for next Tuesday from the morning European model (ECMWF):

500vty_f108_bg_NA

 

Not all that exciting, but there is a cold upper-level trough swinging south over us on Tuesday.  In early February there is plenty of cold air to the north, so that will flow south at the surface and be over us the rest of the week.  Look at the 00z WRF-GFS surface pressure pattern for Wednesday morning next week:

slp.108.0000

That is a strong and very cold east wind.  And with the cold air that deep it’ll flow right over the Cascades too, windy for the entire metro area Tuesday and beyond.  During the December cold spell we didn’t have the strong east wind.and the 850mb temperatures at the same time:

850t.114.0000

Note the -12 or so over Portland, and -20 over The Dalles!  Those are similar numbers to the December cold spell.  Of course that’s a model forecast, not what has actually occurred yet.  But we’re seeing some good consistency in the models; they are all calling for a good cold spell.  It’s just a matter of “how cold?”.  That’s why we dropped the 7 day forecast numbers down so far.    By the way, -20 would equal a high temperature around ZERO at 5,000′ in the Cascades around Mt. Hood.  Yes, this could be one of those times where we get single digits and strong gusty wind up on the mountain!

One other measure of confidence in a colder forecast is the 12z ECMWF ensemble chart:

tseries_850t_000-360_Portland

It shows the operational run was a little on the cold side, but even the average was around a -11 or so by Thursday morning.

Models also show the wettest set of weather systems we’ve seen in 3 weeks arriving beginning NEXT weekend.  Of course that means there maybe be some sort of “transition event” at that time, but that’s still 8+ days away.

Chief Meteorologist Mark Nelsen