Pattern Change!

Wednesday, September 14, 2011
6:38 P.M.

Hi everybody! I slacked off on writing my weather blog this summer, but now I am back and I will resume a regular schedule. Thank you Nicholas Efthimiadis for the friendly reminder to stop being so lazy! In all honesty though, there wasn’t much to write home about this summer. I absolutely LOVED the weather this summer, don’t get me wrong, but from a meteorological standpoint, it was pretty boring in the Pacific Northwest.

But there is change in the air. As you have no doubt noticed, things have cooled down quite a bit over the last few days. This is because we have switched from an offshore flow to an onshore flow. During the summer, the Pacific is cooler than the land of the Pacific Northwest, and during the winter, it is warmer. No matter what time of year it is, an onshore flow helps moderate the temperature, making sure it doesn’t get too hot or too cold. Except for Pineapple Express events in the winter, nearly all of our daily record highs and lows come in a pattern with offshore flow.

12z 9/14/11 36km WRF-GFS
The above graphic shows what the 1000-500mb thickness was like this morning. If you don’t know what that means, search it on this blog, I have talked about it before. Basically it measures the overall warmth of the lower atmosphere. You can see that a thermal trough has pushed to the east of our area. A thermal trough is a local area of low pressure that is created by hot air rising and creating a area of low pressure. It is not associated with rain; in fact, our hottest days on record are the result of thermal troughs.
However, since this thermal trough has pushed eastward, we are now getting strong onshore flow from the Pacific, since air flows from high pressure to low pressure. That is why we have been cloudy and cool as of late.
And as we near October, we should start seeing a strengthening of the jet stream in the Eastern Pacific and a more active storm track as a result. In fact, look at the jet stream right now…
12z 9/14/11 36km WRF-GFS
… and the jet stream five days from now!
12z 9/14/11 36km WRF-GFS
That is a monumental change in the upper atmosphere!  However, we will not feel the effects as much here in the lowlands since the jet stream is still to our north. But be warned, change is on the way!
We will see mostly cloudy skies throughout the next seven days with showers Saturday through Monday. Starting Tuesday, we might get into the low 70s, but I think you’ll have to wait until next year to get back into the 80s.
Tomorrow I’ll talk about our “Double-Dip” La Nina! Who’s ready for round two?
Thanks for reading,
Charlie
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