Snow, New Baby MacMillan, & Summer Heat Next Week

May 16, 2017

10pm Tuesday

What a chilly and occasionally wet day today.  We were only around 50 degrees during the evening commute and topped out at 56 earlier in the day.  It felt more like an early April day didn’t it?  Today was the 6th day with some sort of rain in Portland, that was after a relatively mild & dry start to the month

Today a cold upper-level low was moving over the Pacific Northwest, setting off hail and thundershowers.  Plus a huge snowstorm in the Cascades.  Snow is still falling up there, and about 2 feet has fallen at Timberline Lodge!

Other than some leftover snow on the passes briefly Wednesday AM, we warm up and you can forget about mountain snow.  A big warmup is on the way.

Models have done a very good job forecasting a big change to warm and mainly dry weather beginning the middle of this week.  Sure enough, we’ve got a cold love moving overhead now, but check out the big upper-level ridge that develops right along the West Coast late this week and into early next.  This map is the forecast for Sunday PM.

With 850mb temps moving into the +10 degree range Friday and Saturday, we’ll get well into the 70s (tempered a bit Saturday by onshore flow).  Then Sunday through Tuesday the airflow over us goes northeast or even light easterly.  We’re in “prime sun angle” time of the year now.  We’re getting just as much energy from the sun as we would be in late July.  So with clear skies, 850mb temps +17 to +20, and weak/moderate offshore flow…temperatures are going to soar.  Sunday we should make it into the low-mid 80s.  Then 90 is definitely achievable both Monday and Tuesday.  All global models are in quite good agreement with this “hot” period Sunday-Tuesday.  The record high for Monday is 95 and 93 for Tuesday…it’s not unheard of to see 90 in late May.  Still, it’s hard to believe but we’ll be watering the plants on our decks and in patio containers 6-7 days from now or that Timberline will be in the low 70s next Monday and Tuesday.

As for rain, I think we’re also entering a long dry & mild period, more like what we’d see in June.  As mentioned early next week we’ll see ridging (ECMWF ensemble average 500mb height for Monday)

Then later next week the ridging weakens and backs slightly farther offshore (Friday the 26th, start of Memorial Day weekend)

Then 5 days later…the last day of May…looks similar with that ridging to the west.  This is typically a very dry pattern in spring or early summer with no wet systems approaching from the west.

Check out the ECMWF ensemble 24 hour rainfall chart:

This chart shows the 51 members of the ECMWF model’s “ensemble”.  That’s 51 different versions of the same model run with slightly different initial conditions.  When they are all in pretty good agreement our confidence goes up.  When they are each different, confidence goes down.  In this case each horizontal line is one member and represents 24 hour rainfall.  Notice extremely good agreement that no rain falls Thursday through next Wednesday.  Beyond that you only see scattered showers trying to show up here and there.  So a drier than normal pattern for the next weeks.

On another note, we’ve got a new member of the weather team!  I’d like to call him “Mini-Mac”.  Brian MacMillan & his wife Ashley have a new family member.  Little Evan MacMillan was born late yesterday evening…a solid 8 lbs too.  Congratulations!


Chief Meteorologist Mark Nelsen