cooler

What a change today! A thick marine layer kept us cloudy & gloomy west of the Cascades and then a cold front has passed over the top of that marine layer.  Instead of the 81 we saw Friday, today we only hit 69 in Portland.  A nearly two week period of very warm weather ended today.

High Temp Last 13 Days

Taking a look at the weather maps today it’s obvious that “summer is over”.

What does that statement mean?

  1. The seemingly endless & dependable days of (mainly) dry weather and warm sunshine are finished for this season.  That’s perfectly normal for early-mid September.
  2. The chance of hitting 85-90 again is slim, but still possible
  3. The very warm nights we’ve seen much of this summer will soon be coming to an end.
  4. Expect at least 1″ rain for most of us in the lowlands by the time we get to Tuesday evening, with up to 3″ in some Cascade and Coast Range spots.  Fire Season 2019 will continue to limp along on life support; good news!
  5. Temperatures at pass elevations and Cascade mountain lakes go from 70s yesterday/today to 50s the next few days…that’s chilly camping!

What could we still see?

  1. A briefly hot afternoon.  We can hit 90 even in early October, although it’s rare
  2. Several nice periods of sunny & warm weather; remember those two weeks of sunshine the middle of last October?  Lows in the 40s and highs in 70s were wonderful.

By the way, officially summer ends August 31st according to NOAA; meteorologists consider summer the three month period June-August.  Traditionally of course summer ends at the equinox the third week of September.

The next three days will feature a cool upper-level trough moving over the Pacific Northwest.  This is a classic setup for showers, downpours, thunderstorms, and maybe a funnel cloud or two as well.  All models are showing an unstable atmosphere each of the next three afternoons as the “warm” air bubbles up into the colder airmass overhead.  Ready for some lightning numbers?  Here’s a neat chart showing lightning strike frequency in the metro area for each hour of the day and each week of the year.  You can see two maximums in frequency; late spring & early summer and again in September or very early October (now).  In this situation it’s rare to see it anytime other than afternoons/evenings.  I think it’s interesting that for fall lightning it has a quicker cutoff in the evening, likely due to much earlier sunset than May/June.

multnomah-county-or-week

That upper-level low is right over us Tuesday on the ECMWF ensemble 500mb height chart:

ecm_tues_10th

Then east of here Thursday; that may be the best day of the week weatherwise.

ecm_thurs_12th

Next weekend another upper-level low moves by, but may stay just far enough north to spare us a wet weekend; tough call at this point.

ecm_sun_15th

There are strong hints that we return to drier/warmer weather next week.  See the ridging over the western USA in 10 days?

ecm_wed_18th

As for rain, check out the ECMWF ensembles again for Salem.  Just about every member puts down 1″ of rain, with most of that in the next few days.

ecmwf-KSLE-indiv_qpf-7857600

So hopefully everything you want to stay dry is now indoors or under cover.  Your yard/garden and our woods will get a much-needed soaking!  This growing season has been drier than average across the NW corner of Oregon and SW Washington.  The six month precipitation anomaly:

anomimage

Chief Meteorologist Mark Nelsen

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