The Last Heatwave of the Year

After examining a wide variety of forecast models and considering the region's climatology, it appears we will have to endure only one more warm spell for the remainder of the year.

And by a warm spell,  I mean an event where western Washington rises into the mid-80s or above and eastern Washington nears 100F.

 I will start by showing you the forecasts.  

At Seattle, the skillful NOAA/NWS National Blend of Models (NBM) prediction system forecasts warming to the mid-80s on Thursday and Friday before cooling over the weekend.  Temperatures cool to below normal (upper 60s) next week.  The average high-temperature today in Seattle is 75F for reference.

As a check, consider the highly skillful European Center model ensemble of many forecasts (the mean of these forecasts are shown below).  Quite similar to the NWS prediction.... and this forecast extends through mid-month.

 

Next moving to the Tri-Cities, the prediction for Pasco shows a torrid high above 100F from Thursday to Sunday, with cooling to the lower 80s next week

The temperature anomaly (from normal) forecast (by the European Center) for the mid-month (Sept 13-20) indicates cooler than normal temperatures over western Oregon to near-normal temperatures for the remainder of the region.

Solar radiation and the length of the day rapidly decline in September making it increasingly difficult to get into the 80s by the end of the month.  Check out the monthly solar radiation at Seattle for last year to see what I mean.  September values are WAY down from July.

So why is the heat wave followed by cooling?    

Easy to explain by looking at the upper-level height/pressure pattern at 500 hPa pressure (around 18,000 ft above sea level).  The shading shows the difference from normal, with red indicating ridging or higher pressure aloft.  Blue is roughing or lower than normal pressures.

On Thursday, a strong ridge will develop over British Columbia, with the center in an ideal location to warm Washington State. If this happened in July, we would be talking about mid to upper 90s.

But by Monday,  the ridge had moved inland and a cooling trough of lower pressure will approach. Maybe even a few showers.

The situation later in the week is similar (Thursday).  So still cool.

So enjoy the heat, wear some shorts, and get that swim in.   The heat will soon be over and we will be moving towards fall-like weather starting next week.

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Reminder UW students:  I will be teaching Atmospheric Sciences 101 this fall:

And if you are over 60, you can take the class for $5 through the UW Access Program...either online or in person.