July Weather This Week; Possibly 90 Degrees

May 5, 2019

7pm Sunday…

Forecasting is quite simple the next seven days.  Strong high pressure is sitting just off the Pacific Northwest coastline.  That’s sinking & drying air, keeping weather systems away.

Jet Stream Forecast 2017

That’s why we hit mid 70s in the metro area today, matching our “warmest of spring so far” 76 degree high.

Tomorrow we lose onshore flow, plus a little warmer atmosphere overhead means we’ll likely see our first 80 degree day of the season.  This would be right about on schedule since the 2nd week of May IS the average first 80 degree date for PDX

Average First 70_80_90 Degree Days

We get some brief cooling Tuesday/Wednesday with onshore flow but that only brings us down to 10 degrees above average.  Thursday through Saturday that upper-level high nuzzles right up to the coastline, amplifying at the same time.

Jet Stream Forecast 2017_2

That means surface high pressure develops east of the Cascades and offshore (easterly) low level flow.   Offshore wind May through September can REALLY heat us up under sunny skies and that will be the case Thursday through Saturday.  Most models show onshore flow returning very late Saturday, or Sunday.

So how warm could we get?  Models are generally showing 850mb temps over Salem around 13 to 16 celsius Thursday, then 14 to 18 Friday and Saturday.  To hit 90 in May, past cases show (with offshore flow) we need to see at least a +15 or +16.  So 90 is definitely in the cards this time around.  I’m VERY confident we’re going to hit 85 later this week, far less confident we hit 91-92.

In the past 7 years we’ve seen at least 84 in the first half of May each year.  That said, we haven’t seen a 90 before May 11th for about 20 years.  There you go, lots of numbers.

Rain is a no-show the next week, which means ending Friday we will have seen only .02″ in three weeks!  That will be the driest April 20th-May 10th on record.  Let’s hope this isn’t a repeat of last year.  It would be nice to see a big soaking at some point between now and mid-June.

MarkDrySpellsMay

Starting midweek I’d say it’s time to begin watering everything you would typically water in summertime; lawns, gardens, very small shrubs/plants you just planted etc…  Trees are fine for quite awhile since we had heavy rain just a month ago.

Both the ECMWF & GFS show no rain for the next 8+ days. Click for a better view

That’s through next Monday.  There are still hints we turn wetter around the 14th-18th.  Both ensemble systems show at least some sort of soaking during that time.  That would be later NEXT week

So enjoy the sunshine this week, again, it’s going to feel like July with probably only one “morning clouds” day.  That’ll be Wednesday.

I’ll be off the rest of this week, back to work next Sunday. I’m turning 50 Monday (old!), and randomly chose a week in late April or early May to use up 4 vacation days.  Wow, I sure didn’t expect the weather to line up like this; I think it’s time to get the Nelsen pool up and running!  I’m way too cheap to use a heater so hopefully nature will take care of that Thursday and beyond.

Chief Meteorologist Mark Nelsen


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

Capture

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

ecm_tomorrow

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