Big Picture:

The trough of low pressure responsible for recent cool and wet weather across the Northwest is slowly exiting the region. Meanwhile, a new trough of low pressure will move into California late this week, which will reinforce an active pattern across parts of the West despite an overall warming trend in temperatures. 

Favored regions for showers and thunderstorms from Wednesday through Friday include the eastern slopes of the Continental Divide, Northern U.S. Rockies, and Western Canada. 

Forecast for Wednesday:

A cold front will slide down the eastern side of the Continental Divide, with easterly upslope winds and Gulf of Mexico moisture resulting in showers and thunderstorms along the eastern slopes and adjacent plains from Montana to Colorado. Locally heavy rain will be possible across these areas, with lightning activity favoring Colorado and Southern Wyoming.

Further north, shower activity will be isolated/lighter from Western Montana to Washington, while British Columbia will see more numerous showers and thunderstorms.

Forecast for Thursday:

Showers and thunderstorms will favor areas east of the Divide in Wyoming and Colorado. As the next trough reaches the West Coast, scattered showers and thunderstorms will develop across the Sierra Nevada Range with more isolated activity further north across Washington and BC.

Forecast for Friday:

As the trough moves northeast on its journey inland, it will tap into deeper moisture across the Northern Rockies with widespread showers and thunderstorms expected across Idaho, Montana, and Wyoming along with locally heavy rain. Southern Montana and areas east of the Divide look favored for the heaviest rainfall, and flash flooding will also be possible. 

Elsewhere, an overall drying trend is expected with only isolated showers/thunderstorms across the Colorado Front Range, Great Basin, Sierra, Cascades, and Western Canada.

Forecast for Saturday to Sunday:

Lingering rain will remain possible near and east of the Divide in Southern Montana on Saturday. Otherwise, isolated to scattered thunderstorms can be expected across the Sierra, Cascades, Northern Rockies, and Western Canada. Only a slight chance of thunderstorms is expected at best across the Colorado Front Range and across Northern Utah.

Outlook for Monday (June 26) to Friday (June 30):

Another trough of low pressure will hang around near the West Coast during this period, keeping the best chances of showers and thunderstorms focused across the Sierra, Cascades, Inland Northwest, Northern Rockies, and Western Canada. A dry pattern is expected further south into Colorado and across the Southwest.

Temperatures are expected to remain below average across California and the Great Basin, with hotter-than-average temperatures favoring Colorado, the Southwest, and to a lesser extent, the Pacific Northwest. 

Thanks so much for reading! Next update on Friday (June 23).

Alan Smith