Update to the Potential Record Heat

First, it still looks like a hot weekend coming up.  But the details are becoming a bit muddier.  In our previous blog, the computers were calling for a hot, dry, cloud-free area of high pressure to park over the Pacific NW.  Here's the GFS forecast for atmospheric moisture that was made Saturday evening that is valid for this coming Sunday.

GFS Forecast of Relative Humidity created Saturday 20 June valid Sunday 28 June

The brown color indicates low humidity, which equates to a cloudless sky, while the green is moist areas that would be cloudier.  Now here's the same forecast from the most recent run of the GFS:

GFS Forecast of Relative Humidity created Monday 22 June valid Sunday 28 June

Notice the difference?  See all that green over Washington and Oregon.  That would be a batch of clouds.  The GFS model has changed it's mind a bit.  Why the change?  In the first forecast, the GFS predicted the high pressure to be directly over the Inland NW, which would deflect any clouds/moisture around it, keeping our skies sunny.  Now, the GFS has the high pressure to our east.  Still hot, but it allows clouds/moisture from the south to move up from Mexico and California into the Pacific NW.

Here's the current forecast for Monday.  Still plenty of clouds over the Inland NW.

GFS Forecast of Relative Humidity created Monday 22 June valid Monday 29 June

So what does this mean?  If the clouds do indeed occur, that will help to keep temperatures a bit cooler than previously thought.  Also, this moisture could lead to thunderstorm development over the mountains, which might provide further cooling.  All of this is still just speculation at this time. 

So how hot will it get?  Here's our current forecast temperatures for Sunday.

If this verifies, the 102F at Spokane would not only be a record for the day.  It would be the hottest June day ever in Spokane (the current record is 101F set in 1992).  That's a significant record that could be broken.  In fact, a number of locations could set their record for the hottest June day ever.

But as is usual, the computers have some slight disagreements on the exact temperature.  Here's an example.  The table shows some computer forecasts for Spokane for the Saturday-Monday time frame.

                       Saturday                      Sunday                       Monday
Model A               102                            105                             98
Model B                 98                            103                           missing
Model C                 97                            102                             96
They're all hot, but some are a little hotter than others.

While the potential cloudiness could keep temperatures a little cooler during the day, they would have the opposite affect at night.  Clouds act like a blanket and trap the heat.  This could result in some very uncomfortable sleeping weather, especially if you don't have air conditioning.  Here's the forecast low temperatures for Sunday night. It's possible that a few locations in the Columbia Basin might not cool below 80F.

Again, the weather often comes down to the details, and the details are the hardest to predict, especially this far out.  Suffice to say, it's going to be hot this weekend and possibly the following week.  Just exactly how hot will it be?  Will there be any clouds?  Any thunderstorms?  Those details will hopefully get clearer as we get closer to this event.  We ended the last blog with a reminder:  we had a similar hot forecast for this time of year 2 years ago, and some unexpected showers resulted in cooler temperatures than forecast.