91 in Portland Today; First Soaker of Autumn On The Way Too

September 11, 2017

7pm Monday

Today was warmer than expected; we all made it into the lower 90s in the metro area.

PDX Observed High Today

Some very good news; easterly wind was light as expected and has now switched back to westerly in the Gorge already this evening.  That means all of you (and me) in Level 3 evacuation areas west of Cascade Locks can relax…there’s nothing weatherwise that would cause the fire to take off again in the next week.  Fire lines passed the “East Wind Test” today thanks to all the firefighters who’ve been working on creating containment lines during the cool weather the past 5 days.  Hopefully evacuation levels will be lowered tomorrow.

Back to the heat…notice how many 90+ days this summer in Portland:

MAY: 1
JUNE: 3
JULY: 3
AUGUST: 11
SEPTEMBER: 6

That is the 2nd time we’ve had 24 days at/above 90 degrees in Portland, it happened in 2009 as well.  Only in 2015 have we seen more of these 90 degree scorchers.

90 Degree Days Summer Heat

I think it’s very possible this was our last 90 degree day of the season.  That’s because for the first time since July I see a weather pattern that doesn’t feature warm/hot upper-level ridging nearby.  That’s for the next 10-14 days.

Models do bring one weak disturbance through our area later Wednesday and Thursday, but it’s coming down from the north so expect dry weather.

Jet Stream Forecast 2017

That dry Canadian air moving south means dewpoints (amount of moisture in the air) drop into the 40s Wednesday-Friday.  That combined with long September nights means we’ll have our first “chilly” nights of fall with widespread 40s in the metro area.  But the benefit will be plenty of sun during the day and comfortable afternoon temperatures in the 70s.  Some would say Wednesday through Friday will be perfect early Fall days.  But check out the ECMWF ensemble temperature forecast for Portland for the next 15 days…sure looks different doesn’t it?  No spell of “hot” or even very warm weather.

ecmwf_15daytemps

Note those days in the 60s next week.  That cool spell will be accompanied by our first soaking of the Fall.  There is quite good agreement that a cold upper-level trough will drop in over us Sunday-Tuesday next week.

Jet Stream Forecast 2017b

The ECMWF is painting a large area of 2″+ rain in the Cascades during that time with maybe up to 1″ in the valleys.  This will be our first soaking in 3 months (since mid June).

ECMWF Precipitation Accumulation

If this happens, it could be a season-ending event for some fires in the mountains.  Fires don’t burn well with 2″ of rain plus temperatures in the 40s & 50s…brrr!

So enjoy the pleasant weather the rest of the week and plan on finishing any outdoor projects by Saturday…anything left outside could get very wet Sunday and beyond.

Chief Meteorologist Mark Nelsen