Yesterday evening was simply gorgeous, with clear skies and clean air. I went to bed hoping to awake again to clean air, but alas, it wasn't to be, although I discovered that for once this summer, the mountains offered an escape.
I opted for a quick early ascent of Snowbird so I could return to the valley and get some work done. Although the valley is smoky, Snowbird was clean as a whistle, at least when I summited around 10 AM.
In contrast, smoke fills the valley. If you look carefully at the photo below, taken around 10:35 or so, you can see that the smoke is a bit shallow and doesn't appear to mountaintop level.
What appears to have happened overnight is that there was a weak shift in the wind, with some surface stations exhibiting northwesterly flow that could transport smoke southward into the valley from the north. Hat Island, for example, saw a shift to northerly flow (wind direction blue dots below) just before midnight, which persisted until about 9 AM this morning.
The distribution of fires and the large-scale flow pattern right now is one in which the snow lies to our north and northwest, whereas the clean air is to the south and east. A few hours of northerly flow was enough to bring the smoke at low levels into the area.
Last night's HRRR-Smoke forecast handled this situation really well. Below is the forecast valid at 1800 UTC (1200 MDT) today. Looking for clean air? Head southeast.
If you are wondering, that forecast (the last available since this is an experimental product and only run when computer time is available) keeps us in the smoke through tonight.
It's much nicer in Utah county. Below is the web cam from BYU. If you are looking for clear skies, you could head down there.
Ha ha. Just kidding!