Stable & Dry Summer Weather Pattern Arrives Early

June 27, 2017

10pm Tuesday

Today was about as “average” as it gets for a late June day.  We hit our typical high of 76 with afternoon sunshine following the morning cloud cover.  And of course it was dry as well.  Here in Portland we haven’t seen measurable rain in 11 days:

Mark Dry Spells Summer Recent

Remember that 2012 dry spell?  It didn’t start until early September!  That was a strange early fall dry period.

We have turned dry because those showery spring upper-level lows have weakened and are staying well to the north.   So basically weather maps and models look just like July/August right now and we have entered the warmest/driest time of the year in the Pacific Northwest.  It’s time to hit the rivers, mountain lakes, Gorge, Coast, hiking, camping, bicycling and anything else you wait all fall/winter/spring for. We’ll get just enough onshore flow over the next week to keep hot weather away, but we WILL see a thinner marine layer the next few days.  That means slightly warmer temperatures.

Then a few weak disturbances slide by later this weekend and the first half of next week; that will increase the onshore flow = increasing morning clouds & cooler temps.

Take a look at the Global Ensemble Forecast System (GEFS) temperature anomaly (departure from normal) over the next 16 days.  The general trend is clear…warming the next few days, a downturn but only to around or slightly below average around the 3rd/4th.  Then warming again after the 4th.  A very stable pattern with mainly above average temps.

gefs_anomaly

A different way to look at it; the ECMWF ensemble chart showing maximum temperature from its 51 different members

ecmwf_15day_maxtempensemble

You see quite a few members showing this Friday as the warmest day (the 30th) and then warming again around the 5th/6th.  This shows good agreement among two different models.

As for rain…it looks very dry.  Sure, we can always sneak in some sprinkles or marine air drizzle, but that’s about it.  The GEFS says little or no rain the next 16 days.  Each horizontal line below is one of the 21 ensemble members.

gefs_precip_16days

So enjoy the weather…you’ve waited MANY months for these few guaranteed warm and dry weeks of the year.

By the way, on a side note, today is “melt-out” day at the Mt. Hood SNOTEL Test Site.  This evening the snowpack is just about all gone at that 5,400′ elevation.  The last week it has been melting very quickly.  3 days ago there was 10″ of water content in the snowpack, this evening it will be down to just under 2″ by midnight.  That’s the threshold I use for this graph showing the melt-out date for the past 36 years:

MtHoodMelt

Until the last 3 years the average date hadn’t changed much, but the very early melt-out the past two years (late May and early June) mean the trend is EARLIER for snowmelt AT THIS ELEVATION on the mountain.  We’re only talking a few days, but something to keep an eye on in coming years.  With a warming climate one would assume the date will gradually creep earlier and earlier.  We’ll see.

Chief Meteorologist Mark Nelsen