September: Record Hot 1st Half but October Weather Next Week

September 15, 2017

10am Friday

I just checked the numbers and sure enough, you just survived the hottest start to September on record here in Portland…

First2Weeks

But the payback next week is going to be rough, we’re going straight from July weather to October in just a couple of days.  Those first two weeks of the month blew away any other early September period on record.  The average high was 85 degrees!  Plus we set 5 record warm lows and had the warmest nights ever recorded in Portland in the month of September.  You can see the entire West has been hot, but it’s balanced out by a chilly eastern USA.  This month is a “perfectly normal” month when averaged across the country

conus_mtd_t2avg_anom_2017

And of course this follows the hottest August on record all along the West Coast.

divisionaltavgrank-201708-201708

Now we’re about to see the most dramatic change we can possibly get this time of year.  Remember we’ve had a hot upper-level ridge along the West Coast most of the time since late July.  But beginning Sunday that ridge develops way offshore, in the Gulf of Alaska. Look at the 500 millibar height deviation for midweek.  If it was winter that could give us an arctic outbreak with cold/snow likely:

anomaly_nextThursday

Of course it’s not winter, but this means we’ll go from record warm to near record chilly!  The best part about this pattern change?

I EXPECT FIRE SEASON TO AN EARLY END NEXT WEEK ALL ACROSS THE REGION.  The Eagle Creek Fire is going to be out a week from now if our models are correct.  Take a look at the ECMWF rainfall and temperature forecast for the Portland area for the next 10 days

ecmwf_nextweek

We still expect rain to arrive Sunday afternoon (light rain at first) and then a big soaking Monday and Tuesday as cold showers/thundershowers/hail showers arrive.  Also look at those chilly temps!  High temperatures only in the 60s, maybe even a couple of days where we spend most of our day in the 50s!  That’s a huge change.  Now remember this is just one run of one model, but they are all showing the same thing.  Here is a peek at the ECMWF ensembles; 51 members of the same model showing 24 hour rainfall

ecmwf_24hrqpf

The first half of next week is wet, with far smaller accumulations in the rain bucket beyond next Thursday.

But there’s more!  Just about all the big fires are burning in the Cascades and look at how much rain could fall Sunday through next Thursday…first the ECMWF:

ecmwf_7dayrain

Widespread 2-5″ rain totals on the west slopes and crest of the mountains.  No fire will survive that deluge…excellent news!  Note the valley gets around an inch or so.  Then the GFS model, which has some terrain issues so don’t read too much into all that rain in the metro area:

gfs_7dayrain

Same idea, 2-5″ (or more!) in the mountains and around an inch in the driest part of the valleys.

To summarize…

  1. A VERY DRAMATIC CHANGE FROM “JULY” TO “OCTOBER” ARRIVES SUNDAY
  2. PREPARE FOR ANYTHING OUTSIDE TO GET SOAKED FOR SEVERAL DAYS, FINISH UP ANY OUTDOOR PROJECTS BY SATURDAY EVENING
  3. YOU CAN TURN OFF YOUR GARDEN/YARD WATERING FOR AT LEAST ONE WEEK
  4. FOREST FIRES WILL LIKELY BE EXTINGUISHED OR JUST BE SMOLDERING ONE WEEK FROM NOW

 

Enjoy these next two days, although light easterly wind means fire smoke will be moving around the area as seen in this AM pic from Andrew Mork:

sunrise

Sunday’s rain should put an end to our smokiest summer in memory!

Chief Meteorologist Mark Nelsen