Areas of Fog & A Strong Inversion Continue Through Midweek

FastCast—Tuesday, Jan. 25 to Friday, Jan. 28:

The foggy and stagnant pattern that has gripped the Lowlands is expected to continue for the next few days. Expect areas of fog and some dense fog in spots. Air quality will be moderate at times, especially in areas with lots of wood burning. Highs will be in the upper 30s to low 40s through Wednesday (warmer if fog lifts) and in the mid to upper 40s on Thursday and Friday as the fog becomes less likely. Expect lows in the low to mid 30s. A general pattern shift begins on Friday, with less fog and a chance of showers by late Saturday as the high pressure ridge breaks down.

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Continue reading the full blog below!

The Pacific Northwest continues to be impacted by a persistent high pressure ridge offshore. It is seen below in the European model forecast for Monday evening.

This high pressure ridge has been causing an inversion (where temperature increases with height, instead of decreasing). The sounding below from near SeaTac Airport shows the sharp temperature increase (the blue box) in the first few thousand feet of the atmosphere. Provided by Pivotal Weather.

So what does this mean? Essentially, colder air (and sometimes fog & low clouds) is trapped in the lower atmosphere, but a few thousand feet above, temperatures are much warmer.

A great source to learn more about inversions is Cliff Mass’s 1/23 blog post.

Inversions make for some interesting effects on temperatures. Take a look at Monday’s high temperatures below.

The Puget Sound area reached the upper 30s to low 40s and Ellensburg and Wenatchee didn’t even get above freezing. But look at the mountains…temperatures reached the mid 40s to low 50s above the inversion, the opposite of a usual pattern. 

To see these effects in even more detail…look at this zoomed in view.

Stations near Easton on I-90 and on parts of SR-410 hit the upper 40s to mid 50s, but  Ellensburg didn’t get above 30 degrees! That’s a 20-degree temperature difference between Ellensburg and Easton!

This general pattern, with fog and low clouds at lower elevations and warmer temperatures and sun at higher elevations and on the coast will continue through Thursday, before fog clears up a bit.