Wind Shift Leads to Improving Air Quality For Most Areas This Week:

A large portion of the West dealt with significant smoke and moderate to poor air quality last weekend. The culprit was an outbreak of large wildfires that have impacted Northern Alberta along with portions of BC and Saskatchewan this month. Unlike the Western U.S., this region experienced below-average snowfall this winter, and most notably, has experienced record-breaking heat in late April and May.

Late last week, winds shifted to north/northeast (the direction winds were blowing from), which transported smoke from these fires into the Pacific Northwest and Northern and Central U.S. Rockies.

The good news is that winds are shifting back to a more typical west/southwest direction early this week, which will help to direct the smoke away from the Western U.S. The Interior of BC and Alberta will also see a widespread rain event early this week along with cooler temperatures, which should help with the ongoing fires.

An active weather pattern will also take hold across the Western U.S. this week as a consistent southwest flow pattern sets up, with an abundance of moisture and instability resulting in daily rounds of showers and thunderstorms for parts of the Great Basin and Rockies.

Temperatures will still be on the warmer side of average across much of the West though no extreme warm spells or heatwaves are expected. The exception will be California, especially near the coast, along with parts of the Southwest where temperatures will be a bit cooler than average.

Forecast for Monday (May 22):

A trough of low pressure is located over the Inland Northwest on Monday and will slowly work its way into the Canadian Rockies. The result will be widespread rain across interior portions of BC along with the Northern Alberta Rockies – i.e. the areas that need it the most.

South of the border, strong to severe thunderstorms can be expected across Montana, especially along the eastern slopes of the Divide where large hail (1" or more in diameter) and strong wind gusts will be possible. 

An area of low pressure located over Utah will also result in isolated to scattered thunderstorms across the Great Basin and Central Rockies, extending to areas west of the Divide in Colorado. The Southern Sierra Nevada Range in California will also see some thunderstorms.

Forecast for Tuesday (May 23):

A trough of low pressure will set up near the California Coast and will remain the dominant feature for the foreseeable future. Southwest winds ahead of the trough will transport moisture from the South Pacific into the Great Basin and Northern/Central U.S. Rockies.

Scattered to numerous showers and thunderstorms can be expected for parts of Nevada, Utah, Southeast Idaho, and Western Wyoming where locally heavy rain will be possible under stronger storms. Isolated flooding couldn't be ruled out over burn scars and in areas where streams are already running high due to snowmelt.

Elsewhere, Colorado will also see another active thunderstorm day with drier conditions further south. Lingering moisture from the low pressure system over Canada will result in additional periods of rain across the BC Interior and Northern Alberta Rockies.

Forecast for Wednesday (May 24):

A similar pattern will remain in place with only some subtle regional differences. Southwest flow will favor showers and thunderstorms from the Sierra to the Great Basin and into the Northern Rockies with coverage picking up across Idaho and Montana.

Colorado and Northern New Mexico will also see showers and thunderstorms with an increase in activity expected on the eastern side of the Continental Divide compared to prior days.

The Pacific Northwest will stay dry during this period while Western Canada will also see a drying trend with only some lingering light showers.

Forecast for Thursday to Friday (May 25-26):

A series of disturbances will continue to move across the Western U.S. during this period with showers and thunderstorms expected across the Sierra, Cascades, Inland Northwest, and Northern U.S. Rockies. Colorado and New Mexico will see showers and thunderstorms as well, favoring areas on the eastern side of the Divide.

Outlook for Sat, May 27 – Wed, May 31:

The pattern is not expected to change much over the Memorial Day holiday weekend. A trough of low pressure will remain the dominant feature near the California Coast with relatively cool temperatures, while a tall ridge of high pressure along the eastern side of the Continental Divide will extend northward into Canada, supporting above-average temperatures across parts of the Northern Rockies. 

A moist west/southwest flow will continue to result in good chances for showers and thunderstorms across parts of the Great Basin and Northern Rockies, while moisture from the Gulf of Mexico will also support higher thunderstorm potential east of the Continental Divide. 

Thanks so much for reading! Next update on Wednesday (May 24).

Alan Smith