Big Picture:

The subtropical jet stream will be stretched across California and into the Central Rockies from Friday through the weekend. Disturbances tracking just to the north of the jet will tap into remnant moisture from the Pacific to favor showers and thunderstorms across Montana and the Northern Rockies on Friday and Saturday.

Meanwhile, a cold front will slowly work its way down the eastern slopes of the Divide from Montana to Colorado during the Friday to Sunday timeframe, and easterly upslope winds behind the front will contribute to more widespread showers east of the Divide.

Further west, isolated showers and thunderstorms can be expected from the Sierra Nevada Range to Utah and Western Colorado. Remnant moisture from Hurricane Jova in the Pacific will play a role in shower/thunderstorm activity in this region, but most areas are only expected to see light to moderate (and spotty) rainfall.

Temperatures over the next 5 days will generally be below average east of the Continental Divide from Southern Montana to Colorado, and near average from the Divide westward into California. Temperatures will be above average across the Southwest and across the Interior Pacific Northwest.

Forecast for Friday:

Scattered showers and thunderstorms will favor Montana and Central Idaho, with more isolated activity in Northern Wyoming. Storms across Southwest Montana have the potential to be strong to severe with frequent lightning and significant straight-line wind gusts possible. 

Forecast for Saturday:

Showers and thunderstorms will favor areas east of the Divide in Southern Montana, Wyoming, and Northern Colorado as the cold front works its way southward. Isolated to widely scattered showers and thunderstorms can also be expected from the Sierra Nevada Range to Utah and Western Colorado. A few isolated storms are possible in New Mexico as well.

Forecast for Sunday:

A more active day is expected east of the Divide from Montana to Colorado as easterly upslope winds remain in place. Showers and thunderstorms can be expected with heavier downpours possible.

Also, areas west of the Divide will see an uptick in shower/thunderstorm coverage as well, though activity will still be fairly scattered in nature with lighter rainfall compared to areas east of the Divide. The Southern Sierra could see a few isolated storms but with less activity overall compared to Saturday.

Forecast for Monday to Tuesday:

On Monday, another wet and showery day is expected east of the Divide in Colorado and to a lesser extent Wyoming, followed by a drying trend on Tuesday. The cold front and associated moisture will also reach New Mexico on Monday, where more widespread showers and thunderstorms can be expected on both Monday and Tuesday.

Meanwhile, some late-season monsoonal moisture will work its way into the Southwest during this period with an uptick in thunderstorms expected across Arizona, Southern Utah, and Nevada. Rainfall rates will generally be lighter than what we typically see in peak monsoon season, but some isolated flash flooding couldn't be ruled out in slot canyons.

Outlook for Wednesday (Sep 13) to Sunday (Sep 17):

Lingering moisture is expected to hang around portions of the Central Rockies and Southwest during this period, resulting in continued chances for isolated showers and thunderstorms. Drier conditions are expected across the Sierra, Northwest, and Northern Rockies.

Temperatures are expected to be above average across the Northwest and Northern Rockies during this period. Temperatures are expected to be closer to average across the Central Rockies and parts of the Southwest.

Thanks so much for reading! This will be the final Western U.S. Daily Summit of the 2023 season.

Moving forward, we will be transitioning our weather coverage into the US & Canada Daily Snow starting on Wednesday, September 13th. Also, stay tuned later this fall as our local and regional Daily Snow forecasters begin to post again.

And finally, be sure to check out our New Feature Recap as we have added a lot of new awesome and useful features to OpenSnow this year.

Thanks again for your support!

Alan Smith, Meteorologist