Hot Summer Weather Later This Week

July 8, 2018

9pm Sunday

Today was warmer with highs well into the 80s west of the Cascades.  Meanwhile scorching hot weather continues east of the Cascades.  Everyone east side was in the 90s.

We have a relatively strong marine push in progress this evening.  Check out the visible satellite image showing clouds already moving over the Coast Range:

CODGOES16-local-Portland.truecolor.20180709.030223-over=map-bars=none

So tomorrow and Tuesday will be cooler with highs right around the average for mid-July…80 or so.

What changes the 2nd half of the week?  A huge/sprawling upper-level ridge will be covering about 3/4 of the USA by Thursday…

m500za_f096_bg_NA

notice the 588dm heights covering a huge chunk of the USA at that time?  Notice also that much of North America is seeming higher than normal heights.  That’s something I notice continues well beyond the 7 day period in all the models.  A sustained period of unusually high atmospheric heights instead of a big sharp ridge of high pressure with a downstream trough.  What does that mean?  Models for the next two weeks seem to show a continuously warm/hot period as opposed to a huge heat wave followed by cooling, then more heat.

So how hot could it get over the next week?  Record highs are all 101 or higher beginning Wednesday.  Plus I don’t see a thermal trough west of the Cascades with its easterly wind, so I doubt we get to 100 degrees.  That said, both Wednesday and Thursday the GFS & ECMWF show no onshore flow with gradients flat through the Columbia River Gorge.  850mb temps reach +18 Wednesday (over Salem) and +21-23 Thursday.  That 23 is the ECMWF and its ensembles support the number.  So I forecast 90/98 for Portland Wednesday/Thursday; not record-breaking but the 98 would be the hottest we’ve seen so far this year.  A very weak marine push and 850mb temps down around +19 to +20 Thursday through Sunday means highs retreat to around 90 or just above.

With such a strong/flat upper-level ridge over us, thunderstorm moisture seems to be pretty well suppressed to the south much of the next two weeks.  This is the driest ECMWF precip meteogram I’ve ever seen:

KPDX_2018070812_eps24_precip_360

Enjoy the next two days and then try to stay cool later in the week…

Chief Meteorologist Mark Nelsen