No Heatwaves During the Warmest Time of the Year

 As shown by the temperature plot below for SeaTac Airport, the next few weeks are climatologically the warmest of the year (brown indicates average temperature range, red shows record highs).   SeaTac's average high temperatures during the next weeks are close to 80°F, and many of our record highs have occurred during late July and early August.

There are all kinds of definitions for heat waves, but whatever your definition, model forecasts are pretty emphatic that there WILL NOT be any heat waves during the next week or so in our area.

Consider the forecast by the National Weather Service's National Blend of Models--their most highly skillful temperature forecast system (below).  High temperatures undulate around 80F, with the highest at 85F next Wednesday and the coldest (74F) today.

Every day, the low temperature drops in the 50s.    Very, very average weather.  Perfect weather by my book.

The National Weather Service's Climate Prediction Center's 6-10 day forecast (below) predicts BELOW NORMAL temperatures for western Washington and much of California.   Near normal in eastern Washington. Warmer east of the Rockies.

Do I have confidence it this forecast?  

Yes, because the ensembles of many forecasts....a tool to determine uncertainty in the predictions... shows that virtually all the forecasts are in line with the above forecast.  

To show this,  the GEFS ensemble of many National Weather Service Model forecasts is shown for the next week below.   Most forecasts provide a similar story, and NONE are going for a big heatwave.

You can go to the bank with this forecast 😀.

So what is going on?

Consider the large-scale upper-level weather pattern shown by the heights of the 500-hPa pressure surface (think of this as pressure around 18,000 ft).

Monday morning, there will be a sharp trough of low pressure over our region.....a cold pattern.

Wednesday afternoon, the trough moves out, and an extension of a Pacific ridge/high pressure extends over our region.  This is when our temperatures climb into the mid-80s.

Next Friday, a cold trough moves over the entire West Coast (sweater alert!).

And on Saturday, a sharp, strong trough has moved over Washington and southwest BC.

The bottom line:  no heatwaves and comfortable sleeping at night with AC west of the Cascade crest.

Announcement

I will hold a special online Zoom session at 10 AM next Saturday for Patreon supporters.  Will answer questions,  take a deeper dive on the late summer forecast, and consider the outlook for next winter.