What’s Going On? Warmest May In Portland & Record Dry Late Spring

May 28, 2018

6pm Memorial Day

For the 4th consecutive year we’ve seen a DRY Memorial Day Weekend.  Hard to believe!  But it fits the weather regime we’ve seen for the past 6 weeks…Unusually dry and warm.

We’ve seen a week or two of unusually warm and dry weather in springtime, but this is getting strange.  Folks, we’re living through an unprecedented period of warm and dry weather…one that hasn’t been seen this time of year for at least 80 years, or much longer.

As of today we are experiencing the warmest May on record here in Portland, and in some other spots.  We haven’t seen a single below-average day…just 3 right at average so far…

Mark Monthly Climate Calendar 1

MayTemps

If we add in the next 3 days from our 7 Day forecast, it becomes a tie for #1 with 1992.

Even stranger is the lack of rain.  The past 6 weeks we’ve seen no soaking rain!  The .34″ we’ve seen in the entire 2nd half of meteorological spring (ends Thursday) is less than half of the previous dry record! 

MarkDrySpellsMay

and we’re in the 2nd longest dry streak we’ve ever seen in May…

MarkDrySpellsMay2

I’ve lived west of the Cascades all except maybe 2 years of my life.  Never have I seen it so dry in late May.  My yard/garden/gravel driveway looks just like July…dry and dusty.  In past years when we do get a dry spell in May, we always see a soaking on the maps/models within the next 7-10 days.

Why has it been so dry and warm?  It doesn’t look all that impressive on a weather map, but here’s the 500 millibar height anomaly for the past month.

500mbanomaly

The cool colors are lower than average heights (generally colder than average).  The opposite end of the spectrum are the yellow/orange areas.  You see over SW Canada and NW USA heights have been well above average.   Now it’s typical for upper-level heights to gradually rise from April through August.  But the net effect of that positive anomaly is to push our season “forward” a month or so with heights more like what we would typically see in June or early July.  And in early summer those higher heights typically push weather systems farther north and dry/warm us out/up.

Do we see a soaking ahead?  Likely not a soaking, but there does appear to be an increased chance for a least some dust-settling showers about a week from now.  Check out the ECMWF ensemble 24-hour rain forecast.  Note that any colored horizontal bar says at least .10″ in a 24 hour period.  You don’t see many of those bars do you?  The best chance for showers seems to be right around the 3rd-5th (Sunday-Tuesday), but even that is only appearing on maybe 1/2 of the ensembles.

KPDX_2018052812_eps24_precip_360 (1)

Temperatures WILL be cooler this next week as weak upper-level troughing hangs nearby.  Maybe most noticeable will be cooler temperatures at night due to the dry airmass arriving tonight.  At least that drier/cool airmass helps to break up the marine low clouds so we’ll see plenty of sun the rest of the week…mixed with clouds.  A pleasant end to a crazy warm/dry May!

Chief Meteorologist Mark Nelsen