Forecast Highlights:

• Montana & Northern Idaho: Daily rounds of strong to severe thunderstorms Wednesday to Saturday with strong winds and large hail possible.
• Colorado, Wyoming, New Mexico: Daily rounds of thunderstorms Wednesday to Friday, favoring areas along & east of the Divide. 
• Pacific Northwest: Showers & thunderstorms Wednesday-Thursday, drying trend heading into the weekend.
• Utah & Arizona: Drying trend through Friday, then thunderstorms with canyon/dry wash flash flood potential return this weekend.
• California: Dry and sunny with below-average temps through Friday, then heating up this weekend.

Synopsis:

A stubborn trough of low pressure is located off the coast of Washington, and a series of disturbances associated with this trough will track across the Pacific Northwest and Northern Rockies over the next several days, supporting daily rounds of showers and thunderstorms, including strong to severe thunderstorms across Northern Idaho and Montana.

Drier air south of the trough will push into the Great Basin and Central Rockies, leading to a decrease in monsoonal moisture for areas west of the Continental Divide across the Four Corners.

Meanwhile, a "backdoor" cold front will move into Eastern Wyoming and Colorado on Wednesday and will stall along the eastern slopes of the Continental Divide. This frontal boundary will act as a focal point for thunderstorms along and east of the Divide from Wednesday to Friday.

Forecast for Wednesday:

Disturbances moving across the Northwest and Northern Rockies will result in widespread showers across the Washington Cascades with more isolated/lighter showers further south in Oregon. Thunderstorms will also develop across Northern Idaho and a large portion of Montana with locally heavy rain possible, especially east of the Continental Divide.

A cold front slipping into Eastern Wyoming and Colorado will also result in thunderstorms along and east of the Divide, while lingering monsoonal moisture will contribute to scattered to widespread thunderstorms across Western Colorado as well. Thunderstorm activity will be much more isolated further south in New Mexico.

Similar to previous days, severe weather will be possible with thunderstorms across Montana and even Northern Idaho on Wednesday. The highest threat for severe thunderstorms will be across the Montana ranges and adjacent plains east of the Continental Divide, with wind gusts of over 60 mph and hail of 1" or more in diameter being the main threats.

Isolated severe storms will also be possible across the Black Hills as well as the eastern plains of Wyoming and Colorado.

Forecast for Thursday:

We will see a similar setup on Thursday with showers and thunderstorms across the Northern Rockies. However, showers across the Cascades will be more isolated in coverage and lightning potential will be less here compared to recent days.

Thunderstorms will be more numerous across Northern Idaho and Montana with locally heavy rain possible under stronger storms. Areas along and east of the Divide in Wyoming and Colorado will also be favored for thunderstorms with heavy rain possible, while areas west of the Divide will see a drying trend. Thunderstorm activity will be more isolated in New Mexico.

Severe thunderstorms will be possible once again across the Northern Rockies with large hail and damaging wind gusts being the main threats. 

Forecast for Friday:

Another disturbance will track across the Northern Rockies with scattered thunderstorms developing across Northern Idaho and Montana. Storms should be less widespread and intense compared to recent days, but a few severe thunderstorms still couldn't be ruled out. The Cascades will see a drying trend overall, but a few light showers will remain possible for northern portions of the range. 

Storm coverage will also become more isolated along and east of the Divide in Colorado and Wyoming with drier conditions west of the Divide. New Mexico will start to see an uptick in thunderstorm coverage, however, as monsoonal moisture increases from the south.

Outlook for Saturday - Sunday:

A strong ridge of high pressure centered near the Four Corners will build this weekend, resulting in hot temperatures for portions of the Central Rockies. At the same time, monsoonal moisture will increase across the Southwest and Southern Rockies.

Further north, the last in a series of disturbances will move across the Northern Rockies on Saturday before drying out on Sunday. The Olympics and North Cascades may see a little bit of moisture as well associated with a trough off the British Columbia coast, but most of the rainfall with this system will stay north of the Canadian border.

On Saturday, Northern/Central Idaho and Montana will see another round of thunderstorms, some of which could be strong to severe, followed by a drying trend on Sunday.

Further south, thunderstorm activity associated with the monsoon will gradually spread west and north over the course of the weekend. Flash flood potential will also increase across slot canyons and dry washes across New Mexico, Arizona, and Southern Utah (more likely on Sunday versus Saturday for Arizona/Utah).

Outlook for Monday (7/11) to Tuesday (7/12):

Monsoonal moisture will continue to increase across the Four Corners states during this period with more widespread thunderstorms capable of frequent lightning and heavy rainfall expected. We should also see a gradual northward push of moisture into central and northern portions Colorado and Utah and perhaps Southern Wyoming as well.

Hotter and drier conditions are expected to prevail along the West Coast and across the Northern Rockies as a strong ridge of high pressure continues to build across the Western U.S.

Outlook for Wednesday (7/13) to Wednesday (7/20):

A ridge of high pressure is expected to dominate the Western U.S. during this period with hotter than average temperatures across the board, even in the Pacific Northwest.

However, the monsoon will remain active with abundant moisture across the Four Corners region which should gradually spread northward with time, with a little bit of moisture sneaking into the Northern Rockies as well.

As a result, thunderstorms will be possible throughout the Rockies at times during this period, with heavy rain possible across the Southwest and Southern Rockies. The Pacific Northwest, on the other hand, will see a much drier pattern take hold.

Thanks so much for reading! Next update on Friday (7/8).

ALAN SMITH