Longest Hot Period Since 2009 Ahead, but Probably No Extreme Temps

June 23, 2015

Our longest heat wave/hot spell since 2009 is in the works this morning.  That was the year we hit 106 two days in a row and broke a record for consecutive 90 degree days…10 days!

The bad news?  We likely have a long period (7+ days) of 90 degree or higher temps on the way, the longest since 2009.

The good news?  At this point it doesn’t appear we’ll get much above 100 degrees, if at all, so at least it won’t be too extreme.


1. Hot weather (90 or higher) begins on Friday and appears to last THROUGH MOST OR ALL OF NEXT WEEK!

2. Hottest temps are likely Saturday, although Friday and Sunday will be close.  I think we may just touch 100 degrees Saturday, or it could be another one of those 99 degree days like last summer…we did that twice.

3. With a lack of dry east wind, it’s possible we get into a humid situation through this heat wave.

4. That lack of dry east wind also means it’s unlikely we get the really extreme temps…like 102-107 degrees, that we often see in shorter heat waves.

5.  We may (or may not) see some thunderstorm action either Sunday or Monday, right now only one model is showing that setup.

For the hard-core weather groupies:

I had yesterday off to do some things with the family and the bizarre “July in June” weather was great!  My garden is the best it has ever been this early in the year due to the abnormal heat.  The funniest part of the weekend was Sunday when I was looking for an air conditioner for my elderly parents (thought it would be bad if the weatherman’s parents were suffering in the heat).  My kid’s say “hey, your forecast is on all the fans!”.


Sure enough, the Home Depot in Troutdale was using our forecast to pump up those sales!  Good stuff, and I’m confident they will be gone within a few days.  Too bad I don’t get some free decking lumber in exchange, but that would be Payola.

So I’ve perused the maps and models and two thoughts come to mind.

1. This is going to be a long period of very warm and/or hot weather.  I don’t think we’ve seen this since the summer of 2009.  Take a look at the ECMWF ensemble chart from last night’s run:


Of course this is temperature around 5,000′ in celsius.  The green line is average for this time of year.  At no time (except this morning) does the airmass temperature get down even close to normal in the next 15 days!  That’s the ensemble average red line…a collection of a bunch of runs.  But wait, there’s more.  From later Thursday through the 6th of July (about 11 days) the temperature is +19 or higher…wow!  Generally that’s around 90 degrees or warmer.  If at any point easterly/offshore flow develops, the temp would go much higher.  The 00z GFS ensemble chart looks like this:


It’s not quite as extreme with the temp going down a bit more, but still a long very warm/hot period.

Why so long?  Models have a hot ridge building quickly Thursday/Friday with the core of the heat (center of the ridge) centered close to Boise/NE Nevada.  Check out the ECMWF ensemble 500mb heights for this Saturday:


A scorcher for the entire west.  Hate to be in Boise this weekend!  IF the ridge was to be centered directly over us, as models had shown late last week, we’d be a good 5-10 degrees hotter.

Now notice what changes by the 4th of July (on the ECMWF):


Not quite as hot, but still it prolongs the heat wave.   The ridge is trying to pop up back in its preferred position this past fall/winter/spring…a bit to our west/northwest. I noticed the operational run of the ECMWF has 500mb heights above 588dm from Thursday PM through the following Thursday…a very long period.  Other models are similar but with varying details of course.

2.  At This Point Extreme Heat Looks Unlikely

Your first thought is likely…”what does Mark consider extreme heat; sure looks like it to me“.  I mean 100 degrees and beyond.  As of this morning, models are not showing offshore (easterly) flow except briefly (and weak) Saturday morning.  For our extreme heatwaves in the past, where we see several days in the 102-107 range, we get a sharp thermal trough of low pressure west of the Cascades (in the valley or even at the coast) and gusty easterly wind through the Gorge and over the Cascades.  Because the upper-level ridge is centered to our east, the thermal low is as well.  I remember learning that way back around 1992…in fact I think George Stephan taught me that the shape/position of the thermal low/trough is usually similar to the ridging and I’ve noticed that over the past (shudder) 23 years since that time.  To get a sharp thermal trough westside (and extreme downslope heating) you need a ridge right overhead or to our north (90% of the time).

To make a long story short, we’ll have weak onshore flow during most of this hot spell.  That may lead to another unusually humid hot spell too, we’ll see.

As for thunderstorms, the setup could be right Sunday or Monday, but the ECMWF and GEM don’t show any moisture for storms so I’m not real excited about that possibility right now.

Chief Meteorologist Mark Nelsen