Hot Way to End the Summer - Update

In my last blog I mentioned a couple of things worth repeating: 1) there was no guarantee that we would see cooling by the weekend, and 2) there’s never been a 100F reading at Spokane Airport in September. Well, the computers are coming into better agreement on #1, and that could have implications on #2.

First, let’s revisit the current weather map. Strong high pressure dominates the western coast of North America while a deep cool low pressure is giving the eastern US early fall weather. 


What isn’t so obvious is that there’s actually a very minor low pressure disturbance over Oregon that will affect our weather.  Let’s look at a satellite image to see what I’m talking about.


It’s actually made up of three circulations.  Rather complex, but also rather weak. They will very slowly move northward over the next few days, bringing with them a lot of clouds and moisture.  This is going to affect our weather in several ways.  The first is that we will see some gradual daytime cooling as the increasing clouds block the sun’s rays. This will just be a few degrees cooler on Tuesday and Wednesday; highs will still be in the 90s. But thicker clouds on Thursday could drop daytime highs back into the 80s.

However, this moisture will also raise our dew point into the 50s, possibly even lower 60s.  So while the temperature might not be as hot, it will feel muggy.

But all this clouds and moisture will also affect our low temperatures at night.  The current dry air and clear skies allows our temperatures to quickly cool into the lower 50s and 40s.  But during the next few days, the clouds will keep us warm at night, with temperatures only dropping into the 60s.  A big impact for those without air conditioning.  Here’s the forecast low temperatures from the European model for Wednesday morning (Thursday morning looks similar).


This weather disturbance could also bring some rain.  But as I mentioned, it’s very weak.  So the showers and thunderstorms will be spotty and mostly light, mainly on Wednesday and Thursday.  Here’s the European rainfall forecast for those two days.  Don’t get hung up on the exact locations of the showers.


Since our cooling is mainly due to cloud cover rather than a strong cold front, we won’t see any strong winds this week, which is good news for wildfire concerns.  

However, once the clouds are gone, the lack of a cold front means that temperatures will just warm back up for the weekend.  In fact, hot temperatures are forecast to continue into the first week of September.  

The European computer model is actually predicting a high of 100F for Spokane next Tuesday (Sept 2), and 99F for Wednesday.


Now, odds are that the actual high temperature on those days won’t hit the century mark.   If it does, it will be the first time in Spokane Airport history that at 100F was reached in September.  (Technically the downtown Spokane Felts Field sensor hit 100F on 1 September last year, and almost touched that mark again a few days later on 7 September).





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