Western US Daily Summit

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T-Storms Favoring the Sierra, Rockies, & Inland Northwest


An active pattern will continue across the West this weekend with two main focus areas of showers & t-storms. The first will stretch from the Sierra Nevada Range up into the Cascades (favoring the eastern slopes) and Inland Northwest, as well as parts of Canada. The second focus area will be across the Rockies from Montana to Colorado favoring areas near and east of the Divide.

Short Term Forecast

Big Picture:

The large-scale pattern will remain similar to recent weeks with a tall ridge of high pressure extending into Northern Canada, while a trough of low pressure will undercut the ridge to the south across the Western U.S. 

The next trough will slowly work its way into California on Friday and into the weekend with south/southwest winds on the downstream side of the trough transporting subtropical moisture into the Sierra and Interior Northwest, as well as the Northern Rockies. 

Meanwhile, "energy" downstream of this trough will also work its way into the Central Rockies and will interact with Gulf of Mexico moisture approaching the Rockies via easterly winds. This will favor thunderstorm activity along the eastern side of the Continental Divide. 

Forecast for Friday:

As a trough of low pressure approaches the West Coast, a surge of moisture will move from south to north into the Pacific Northwest, with showers and thunderstorms developing along and east of the Cascade crest across Oregon and Washington and into British Columbia. These regions along with Northern Idaho/Montana could see heavy rainfall and localized flash flooding under stronger thunderstorms.

Areas west of the Cascades into the Puget Sound region and Olympic Peninsula as well as the BC Coast Range will see showers as well, though rainfall will be lighter and lightning potential lower. 

Isolated to scattered thunderstorms can also be expected across the Sierra Nevada Range, Great Basin, Idaho, Utah, Wyoming, and along the Colorado Front Range. 

Forecast for Saturday:

Moisture will increase across California with more widespread showers and thunderstorms expected across the higher elevations with locally heavy rain possible, especially in the Sierra. The Cascades will start to see a drying trend while scattered to numerous showers and thunderstorms can be expected across the Inland Northwest as well as BC and Alberta.

Further east, showers and thunderstorms will favor the Northern Rockies in Idaho, Montana, and Wyoming with heavy rain and localized flash flooding possible east of the Divide in Wyoming. Thunderstorms will be more scattered to isolated in nature across Utah and Colorado.

Forecast for Sunday:

A further uptick in showers and thunderstorms is expected across California and Nevada with heavy rain possible under stronger storms. Eastern Washington/Oregon will begin to see a drying trend while showers/thunderstorms can be expected once again from the Northern U.S. Rockies into Eastern BC/Western Alberta.

Further south, an uptick in thunderstorms is also expected across Northern Utah as well as Central and Eastern Colorado. Locally heavy rain and flash flooding is also possible east of the Divide in Colorado. 

Forecast for Monday to Tuesday:

Showers and thunderstorms will favor the Sierra, Great Basin, Idaho, and Western Wyoming/Montana. Scattered thunderstorms can also be expected across Utah and Western Colorado, with the potential for stronger thunderstorms and locally heavy rain east of the Divide in Colorado. 

Extended Forecast

Outlook for Wednesday (June 14) to Sunday (June 18):

A wetter-than-average pattern is expected to continue across a large portion of the West during this period with frequent afternoon showers/thunderstorms. Areas with the highest odds of above-average rainfall include the Wasatch and the Tetons/Yellowstone. The only region where below-average rainfall is expected is across New Mexico and portions of Arizona.

Temperatures are also expected to be cooler than average across the West Central and Southwest, while the Pacific Northwest and far Northern Rockies should not deviate much from average.

Thanks so much for reading! Next update on Monday (June 12).

Alan Smith