Excellent “Early Summer” Weather Ahead

9pm Sunday

What a beautiful day across the Pacific Northwest!  Even the coastline cleared out as temperatures rose into the 70s out there

Here in Portland we saw our 2nd warmest day of the season so far (May 4th at 85 was warmest).  Easterly wind came over the Cascades and through the Columbia River Gorge…it was light but it got the job done (warming).  Troutdale was the warmest spot in the metro area as the easterly wind mixed down dry and warm air from above.    You can see a thick layer of easterly flow on the Troutdale profiler (current time on left side, two days ago on right)

850mb temps are expected to top out around +19 over Salem tomorrow afternoon as a 588dm ridge centers just offshore of the Pacific Northwest.  This means that warm easterly flow of warm and dry air increases tonight and tomorrow, warming the atmosphere further.  As a result the western valleys should see a 5-10 degree warming Monday and a few spots on the coastline will get above 80 degrees (Tillamook).  Monday is going to be a “May Scorcher”.  The good news is that it’ll only be for one day.  A couple of nights ago models began to show the ridging “squashing down” much faster as a cold system drops through SW Canada late Tuesday & Wednesday.  They have stayed with that idea which means a few things:

1. Temperatures will likely peak earlier than normal Tuesday (early to mid-afternoon) as a strong northwest wind begins to blow west of the Cascades.  Gusts to 30 mph are likely by 5-8pm as a much cooler airmass pours inland.
2. Highs will just get a few degrees above 80 on Tuesday…it won’t be a hot day
3. Wednesday will be dramatically cooler
4. Wednesday will NOT be a gloomy day.  That’s because a cold and quite dry upper-level airmass will disrupt the typical warm season marine layer that would give us gray skies and drizzle.  Wednesday will be breezy, cool-ish, and nice late May day

What happens beyond Wednesday as we head toward the first big holiday of Summer 2017?

Believe it or not, there is some good news…it’s possible we have a very nice 3 day weekend on the way.  I’m scared to jinx it, but as of now there is pretty good agreement that upper-level ridging is going to rebuild along the West Coast.  Nothing extreme, but a very pleasant June-like pattern with above normal temps and mainly (or all) dry weather.   Check out the 12z ECMWF model 850mb ensemble chart.  This shows the next two weeks.

The green line is average temperature in celsius for the date at around the 5,000′ elevation.  Blue line is operational ECMWF run, red is ensemble average.  The screaming message here is that we’ll have that brief chilly day or two Wednesday & Thursday, then a warming trend that just happens line up with Memorial Day Weekend.  I’ll have to check the records and see when we last had a warm and mostly sunny Memorial Day Weekend…can’t remember.  Confidence is relatively high since NO ensembles are below average until AFTER the weekend.

One other interesting tidbit…from the GEFS (GFS ensembles).  This is a rainfall chart for the next 16 days, each horizontal line represents accumulated rain as you go from left to right (current time is left side).  Note only 1 of the 21 ensemble members has measurable rain before May 31st.  That’s a week from Wednesday.

 It appears May is going to end on a mild and mainly (or all) dry note.  That’s quite a change.  If this is the case, it’ll break the 5 month cold streak we’ve had going since December.  And it’ll be our first drier than normal month since January…it’s time I suppose.

Enjoy the sunshine and stay cool tomorrow.  At least it’ll only be hot for a few hours in the afternoon.

Chief Meteorologist Mark Nelsen