We are now experiencing the most sustained stretch of summer to fall weather in years, with one of the symptoms being the longevity of some of the region’s smoldering fires.
And the smoke from these fires reveals some interesting aspects of local meteorology and topographical influences.
Yesterday afternoon, smoke could be seen from the fires in Bolt Creek and Lake Wenatchee heading west to west Washington. Solar heating during the day revived the fires and helped mix the smoke vertically, where it was picked up by winter (eastward) winds of the lower atmosphere.
NASA MODIS image at around 1 p.m., Saturday
Overnight, as the surface and lower atmosphere cooled, the vertical mixing was greatly weakened and the cool air tended to move down the valley in the direction of lower elevation.. . on BOTH sides of the Cascades.
To illustrate, take a look at the satellite image visible at around 8 a.m. this morning (Sunday).
Smoke from the Bolt Creek Fire is moving west down the Skykomish Valley into western Washington, while the smoke from Lake Wenatchee follows the Wenatchee River Valley eastward into Leavenworth and the Wenatchee area.
Both of these “valley smoke streams” are released as they come out of the mountains.
Smoke not only degrades air quality, but also affects clouds. Take a close look at the Snohomish River valley east of Seattle – can you see the fog there?
PurpleAir’s air quality observations clearly show the unfortunate effects of smoke (see below). The Bolt Creek plume is escaping around Monroe and then sweeping south through Seattle’s eastern suburbs. Air quality is much better near Sound.
Smoke plumes over the Wenatchee River are associated with very bad air quality from Lake Wenatchee through Leavenworth to the Columbia River.
Tomorrow (Monday) will be the same…sorry.
Problem
The atmosphere is deadlocked. The atmospheric circulation has been locked into a very stable pattern with a high pressure peak on the West Coast and two grooves on the sides – known as the Omega Model.
Take a look at a series of upper level maps (500 hPa, about 18,000 ft) showing elevation above sea level (you can also think of this as pressure at 18,000 ft). Red indicates presence/high pressure and blue/green the opposite.
This morning there is a peak in the western US and grooves on both sides. An omega model).
The situation late on Thursday was similar by an even higher margin. This means that the Northwest is dry and warm.
And the forecast for October 12 is simply phenomenal. An omega model on steroids.
We may not see a drop of rain before the middle of the month. Have we ever had the first half of October completely dry?
Here’s the data for Seattle…. the answer is yes… several times.
Curiously, this hot-dry pattern would stave off new wildfires from western Washington and Oregon, as well as California.
Atmospheric Science 101
Like last year, I’m teaching atmospheric science 101: a general introduction to weather and climate, this fall. You can learn more about the class on class website. I talk about everything from atmospheric basics to weather prediction, thunderstorms, storms, and local weather to climate and global warming.
I will be teaching the class in person at UW, but will also be delivering it via zoom. So people can get it remotely.
If you are over 60 years old, you can join the class via Access Program for a very small fee (about $15). Last year, I had over 125 people do so.
So, if you are a UW student looking to learn about the weather or a student who is not interested in the subject, I welcome you to join me this fall. My first class was on September 29.
