It’s been a terrible 2nd half of winter for cold and snow lovers in the Pacific Northwest.  After a strong start to the season, things died down a month ago and there’s no sign of an active pattern picking back up in the next 10-12 days either.

But if the weather remains boring long enough, a different kind of excitement can develop as the February sun increases in strength.  Late this week, we are looking at a classic ‘False Spring’ pattern to emerge in our area.  Temperatures in the lowlands of NW Oregon and Washington should climb to near 60 degrees for at least 2 or 3 days.

That said, we don’t have a clear idea on just how warm the Portland-Vancouver area will get at this point.  The problem is that it’s only the 2nd week of February and the sun is still no stronger than it was in late October.  That’s enough to weaken the inversions under a strong ridge somewhat, and allow fog to burn off in the afternoon better than it does in December or January.  But some inversion usually remains, unless we get extremely lucky and east wind mixes out the cool air at the surface.  Even then we still have to be careful:  if a pool of cool air develops in the Columbia Basin, that east wind can end up pulling in low-level cool air through the Gorge instead!

First of all, the upper-level airmass is definitely going to be warm and dry for the remainder of this week and weekend.  Check out this GEFS spaghetti chart, the 12z from earlier today:

As you can see, from Thursday afternoon (the 11FEB mark at the bottom is actually 4pm on Thursday the 10th) through Sunday afternoon, the airmass will be extremely warm by February standards – between 11 and 14 degrees Celsius.  Also plenty of dry air and sunshine coming in.  But will that sunshine be enough to mix out the haze and fog in the lowest levels?  If not then we would stay in the low/mid 50s for highs with fog at least lasting through a good chunk of the morning.  If the inversion breaks a little more, then we go up to near 60.  And if a downsloping east wind stirs things up even more, we could get up to 63-65 for a day or two.  In short, we’re right on the “edge” of inversion season and that makes lowland temperature predictions rather difficult in a pattern like this.

The WRF-GFS maps are pointing to a different kind of inversion problem though:  cool air settling in the Columbia Basin and coming through the Gorge as a strong low-level east wind.  Here are the 4pm surface temperature maps for Thursday, Friday and Saturday.  The orange zone is 56-60 degrees F; the red is 60-64, and reddish-pink is 64-68.  Pay close attention to what happens in northwest Oregon and southwest Washington between Thursday and Friday afternoon:

My gut feeling is that the WRF-GFS is probably overdoing the cooling effects of Gorge wind.  Mainly because the east side doesn’t cool down quite enough for that kind of stuff.  If The Dalles and the Tri-Cities stayed in the 40s all day Friday, then we would probably see a lot of “bleeding” of cooler air into NW Oregon.  But even in the middle of winter, it often takes a couple days for east-side inversions to take their full toll on west-side temps.

Once the Gorge wind gets going Friday though, it will probably feel cooler east of I-205 in Portland.  (That is actually  one of the main reasons why I’m happy not to live there anymore!)

Here is the regular 00z GFS image for Friday 4pm, which shows upper 50s to near 60 across our area:

In the short term, tomorrow and probably Thursday morning should see plenty of fog.  With no high clouds to interfere with incoming solar radiation, I think we will see a warmer/sunnier afternoon than we did today.  Temps likely rebound into the mid 50s as a result.

Thursday’s temps  are a bit of a wild card.  Could be 55, or closer to 60 if fog is quick to break up.  Then Friday-Sunday the east wind picks up and fog disappears from the area.  That will probably make it easier to reach 60, unless the wind gets unexpectedly strong and chilly.

Temperatures along the coast and in southwest Oregon turn extremely warm by Friday, with a number of locations likely in the 65-70 degree range.  By the way…if this pattern was happening 2 weeks later, in the last week of February?  Then Portland could be spectacularly warm, with mid or even upper 60s .

The party ends by Monday as cooler air and a chance of showers move back in.  We should go from way above normal temperatures, to slightly below normal – which in the middle of February means upper 40s.

There is no sign of any serious cold or low-elevation snow in the next 10 days.  That likely means we’re done with any serious winter cold events for the season.  But we can still get a dusting of lowland snow well into March, and heavy snow in the Coast Range and Cascade foothills, if the pattern turns chilly again! -Karl