A hot and dry summer across a large portion of Western North America has resulted in widespread fire activity from California to Idaho to British Columbia. Many of these fires have been very large, and over the past month smoke has been persistent across much of the West. However, the seasons are beginning to change as we near the end of August, and there are some clear signs that fall is right around the corner.
In general, the Western U.S has already been experiencing cooler temperatures over the past 1-2 weeks compared to a hot first half of August west of the Continental Divide. Today, a more substantial change is occurring as a deep trough of low pressure is pushing into the Northern Rockies, resulting in unseasonably cool temperatures along with much needed moisture. The image below shows the height anomalies at the upper levels of the atmosphere, which depict this fall-like system well over Montana and Wyoming (source: weathermodels.com).
Even though the calendar says late August, this system has a wintery side as well, and snow is falling at the higher elevations of the Northern Rockies, including Grand Teton, Yellowstone, and Glacier National Parks. The webcam image below shows fresh snow near the top of Jackson Hole Ski Area in Wyoming.
The moisture, cold temperatures, and snow with this system should help out with the wildfire the smoke situation. While this system won’t totally extinguish wildfires in the Northern Rockies, it will certainly help to reduce fire behavior, and most areas should see significant improvement with regards to smoke and air quality this week as a result. The exceptions will be in areas such as California and Nevada, which are missing out on the moisture.
Farther south, Colorado is on the dry side of the trough and jet stream today, and as a result hot, dry, and windy conditions are present across the Front Range instead. The fire danger is elevated here today as a result, but fortunately a cold front will arrive tonight with much cooler temperatures on Tuesday. Some parts of Colorado could see some light showers on Tuesday, but in general the state will be missing out on significant moisture with this system. Upslope flow pooling east of the Continental Divide could bring some more smoke to the Front Range on Tuesday, but then improvements are expected for the remainder of the week.