Another Unusually Warm & Dry Start to May

May 2, 2019

6pm Thursday…

Today was a typical “morning clouds then afternoon sun” day west of the Cascades.  We had a relatively strong push of marine air overnight.  That marine layer is thinning now which means less morning cloud cover Friday + more sunshine.  That equals warmer temps; although today’s 66 in Portland only came down to average for May 2nd

Todays Observed Highs OrWa 2017

We have a very nice early May weekend on the way.

Onshore flow weakens dramatically Saturday for a good 6-10 degree jump in temps with little/no morning cloud cover west of the Cascades.  That should push us into the mid 70s.  Expect similar weather Sunday, although several models are bringing a better push of morning clouds & cooler temps that day.  Regardless, a dry May weekend with plenty of sunshine plus temps above average = very nice!

But now things are getting strange again…

During the past two weeks we’ve seen little/no rain for most of us west of the Cascades.

1. That DOES sometimes happen in the springtime for a week or so, but dry spells to two weeks are unusual.

2. Now add in another week of dry weather on the way and that’s VERY unusual.  I just took a look at rain records here in Portland.  This is crazy.  Take the last two weeks of April, then add in these first 9 days of May (assuming little/no rain falls through next Thursday).

3. This year is the driest, followed by…last year!

Three of the five driest late April through early May periods have been in the past few years.  That’s 2019, 2018, & 2015.    We know what happened in those other two years…very warm/hot summers.

We have also seen 6 consecutive dry Mays in Oregon Climate Zone #2 (lower elevations west of Cascades).  That’s after the memorable chilly & wet springs 2010-2012


This does make me suspect (along with other evidence) that our warming/changing climate has a part in this.  Anecdotally, it seems we are seeing more episodes of upper-level ridging near/over the west coast of North America the past 5-6 years.  Remember last winter we (again) didn’t have any sort of typical stormy westerly flow.  The action (snow & cold) came from a big ridge to our west and cold northerly flow coming out of Canada.  Also it seems we are seeing higher “upper-level heights” in the warm season.  In this case everything would be pushed to the north; Portland’s warm season weather would become more like Roseburg.  Then Roseburg is more like Medford etc…  Again, this is anecdotal and based on what I’ve seen all these years forecasting in our area.

As Pete Ferryman said yesterday, maybe the old saying “summer begins on July 5th” will disappear in time.  We’ll see.

In the short term we have a very stable pattern offshore with an upper-level ridge over a cool upper-low approaching California


That ridge strengthens and snuggles right up to the Pacific Northwest through the middle of next week.  Notice ensemble averages of the ECMWF, GFS, & GEM models all show the same setup for NEXT WEDNESDAY.  At this point 850mb temps climb above +10 and offshore (easterly flow) may develop

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If so, we’ll see our first 80s of the season the 2nd half of next week.  Here are the forecast numbers I’m using tonight:

Forecast Highs Next 7 Day Meteogram DCA

Our average high temperature now through May 9th is 65-67 degrees so this is well above average.  Not record-setting by any means since they are around 90 this time of year.

What about rain?  Both the GFS and ECMWF ensemble members say we might see some sort of cooler/showery pattern show up around the 13th/14th.  That’s still quite a way off.  Click for a better view


Enjoy the weekend!

Chief Meteorologist Mark Nelsen