Superheat Coming to the Northwest This Week

If you were thinking about buying a fan this summer, I would hit the stores soon.

If you were thinking of picking up an AC unit, I would take care of that right away.

Big heat is coming to the Northwest later this week, with record breaking temperatures for many, particularly on Thursday, the warmest day.  We are talking about mid to upper 90s F around Puget Sound, and 105-110F near Portland.

During mid-week, a huge ridge of high pressure will build over the western U.S. (see upper level map--500 hPa level--for 5 PM Thursday).

The WRF forecast surface pressure map (with lower atmosphere... 925 hPa, roughly 3000 ft.... temperatures) shows the classic heat wave pattern, with low pressure (thermal trough) extending into western Washington and easterly flow over Cascades.

Take a look at the 5 PM Thursday surface air temperatures (at 2 meters) forecast by the UW WRF model (below).  Mid to upper 90s around Puget Sound (cooler right next to the water) and  over 104F across SW Washington and the Willamette Valley.   I need to change the temperature scale for such heat waves!

Weather.com has excellent forecast and they are going for 95F at Seattle-Tacoma Airport and an AMAZING 110F at Portland.  Keep in mind that this would be higher than the ALL TIME MAX temperature at Portland (107F).

Seattle

Portland

But how confident are these forecasts?  What are the uncertainties?   

As I have described many times in this blog, one should turn to ensemble forecasts (running the model many times with slightly different initial conditions and physics).   Let's start with the best ensemble system, that of the European Center, for Seattle Tacoma Airport.  Their single high resolution forecast is shown by the black line, the mean of the ensemble by the green line, and the spread of the ensembles by the whiskers and green boxes (the whisker are the extremes of the ensembles and the boxes show you the 50 percent of the forecasts closest to the median).

On Thursday, the high-resolution (deterministic) forecast is going for about 97F and the ensemble mean is ABOVE 100F!  Crazy warm.

The US GFS ensemble is peaking around 96F and all the members are very warm.  But one good thing...temperatures will cool down into the 60s at night, so with a good fan you will be able get your rooms cool enough for sleep.

The bottom line of all this information is that we have great confidence of a major warm up, with Thursday heading above 95F. I suspect several locations in the eastern suburbs of Seattle will hit 100F.   And SW Washington, Portland, and the Willamette Valley will exceed the century mark by 5-10F.   And the ensembles show the potential for even warmer conditions.

On second though, perhaps you should run to buy that fan tonight....

from Cliff Mass Weather and Climate Blog http://ift.tt/2uJjsHP