Big Picture:

A trough of low pressure will be moving across Western Canada and the Northern U.S. Rockies on Monday and Tuesday with the jet stream moving through Southern Montana.

This feature will tap into residual moisture to result in a good chance of thunderstorms across the Northern Rockies through Monday afternoon, some of which could be strong to severe. The threat will shift southward into the eastern ranges of Wyoming and Colorado behind the passage of a cold front. 

Once the front clears the Northwest and Northern Rockies on Monday night, a little bit of smoke from wildfires in Northwest Canada will make its way into the PNW of WA and OR, with only some residual smoke expected further south and east. Smoke across the PNW should clear out later this week (likely Thursday) as winds shift from northerly back to westerly.

Across the Southwest, hot, dry, and windy conditions can be expected on the southern side of the trough moving across the Northern Rockies. This will result in elevated fire weather concerns across Northern Arizona, Southern Utah, and Western Colorado. 

Forecast for Monday Afternoon to Monday Night:

Thunderstorm activity will favor Southern Montana and Northern Wyoming on Monday afternoon/evening with stronger storms possible, capable of frequent lightning, gusty winds, and moderate to large hail.

The greatest threat for severe weather will be across NE Wyoming from the Bighorns to the Black Hills, where the main threats will include large hail, damaging winds, and possibly a tornado.

Storm coverage will be more isolated across Northern Montana, as well as southward into Northern Utah and Western/Central Colorado. Dry and sunny conditions are expected further west.

Forecast for Tuesday (4th of July):

Independence Day is shaping up to be an active day for areas near and east of the Divide across the Central Rockies. In fact, Beartooth Pass and some of the higher terrain across the Beartooths/Absarokas in Southern Montana could wake up to some wet snow in the morning. 

Thunderstorm chances during the afternoon will be highest across Central/Eastern Wyoming and Central/Eastern Colorado. Strong to severe thunderstorms are also possible along the eastern slopes of the Divide in Colorado and out onto the plains, with large hail and damaging winds possible. 

Isolated thunderstorms will be possible from Northern Utah to Central Idaho with drier conditions further south and west.

Forecast for Wednesday:

A gradual drying trend from west to east can be expected, but the Front Range and Sangre de Christo Range in Colorado (as well as Northern New Mexico) will remain the focal point for thunderstorm activity. Strong to severe thunderstorms will be possible once again over the eastern foothills and out onto the plains.

Isolated storms are possible across the Northern Rockies with drier conditions further west.

Forecast for Thursday to Saturday:

On Thursday, another trough will move into the Western U.S. and will tap into residual moisture to result in isolated thunderstorms across the Northern Rockies. On Friday, the focus will shift to areas along and east of the Continental Divide across Wyoming and Colorado. Shower/thunderstorm activity will also increase north of the border across BC and Alberta. 

Outlook for Saturday (July 8) to Wednesday (July 12):

High pressure will strengthen across the Southwest during this period, resulting in mostly dry conditions while disturbances will continue to sneak across the Northern and Eastern Rockies, resulting in occasional thunderstorms.

While the Southwest is dry for now, we are starting to see some signs of early monsoonal moisture working its way into Arizona/New Mexico by around mid-month, so this will be something to keep an eye on.

Temperatures are expected to be hotter than average across much of the West during this period, with exceptions including areas east of the Continental Divide in Montana and Wyoming.

Thanks so much for reading and Happy Fourth of July! Next update on Wednesday (July 5).

Alan Smith