First Heat Wave of 2013 On The Way

June 27, 2013

6:30am Thursday…

It looks very likely now that we’re headed into a stretch of hot weather to start July, I’ve got an update for you

The Basics:

  • Temps top out around 90, give or take a few degrees, Friday-Sunday in the western valleys, including Portland
  • Quite a bit warmer (hotter) Monday-Wednesday.  High temps somewhere between 95-105 degrees.  At this point the most likely scenario is hottest temps Tuesday with a high right around 100 degrees!
  • Humidity…rarely do we have humid conditions at the same time as hot weather; this will be one of those times.  We may see low temperatures close to 70 early next week, very unusual.

The Details:

I’m still at the weather conference in Nashville, thus the early start!  Models have become quite a bit more organized with the approaching hot ridge of high pressure for early next week.  Upper level ridge seems to be strongest and almost right over us Monday-Wednesday.  Here is the 500mb forecast for Tuesday morning from the ECMWF.

ecmwf_500_tue

Look at those heights!  A 597dm closed high over Eastern Oregon?  I don’t remember the last time I’ve seen heights that high so close to us.

This is an unusual setup that I haven’t seen in many years;  a highly amplified ridge with the sharp and deep upper low well offshore.  Usually we just have a bulky-looking ridge and the appearance is a bit flatter.  The GFS continues to produce much warmer 850mb temps (in some runs) than the ECMWF.  It also has the ridge slightly farther west (right on top of us), giving stronger offshore flow Tuesday-Wednesday.  It would say we’re up around Portland’s record high (107) during that time.  Considering it’s past performance, I’m ignoring it for now.  The ECMWF tops out those temps somewhere just under +25.  With flat or weak offshore flow Tuesday, I could see a high temp at PDX very close to or at 100 degrees.

You can see the difference in the two ensemble charts, the 00z ECMWF and 06z GFS:

tseries_850t_000-360_Portland

tseries_850t_000-384_Portland

Let’s talk humidity…it looks rough this time around!  We have two things going on.  First, plenty of moisture is just sitting over the Pacific Northwest from the recent rainfall, not necessarily just in the ground, but the airmass is very moist.  We’ve got dewpoints around 60 this morning.  Then a capping ridge of high pressure settles overhead without a period of drying north or northeast wind.  AND, areas to our north and east have been wet too.  Models show the humidity hanging around.  This means warmer than normal nights ahead and humid days.  If we get up around 95-100, we could easily have low temps around 70 degrees!

Get ready to hit the water, stay in air-conditioned places, or just plain sweat a lot over the next week!  The bonus is this kind of weather produces wonderful  evening and early morning weather, you’ll step outside and feel warm at sunrise…how “strange” is that?

Chief Meteorologist Mark Nelsen