Forecast Highlights:

• Montana & Northern Idaho - Strong to severe thunderstorms Friday to Sunday.
• Colorado, Utah, Arizona - Thunderstorm activity decreases Friday-Saturday, picks up again Sunday and beyond.
• New Mexico - Thunderstorm activity ramps up from Friday through early next week.
• Wyoming & Southern Idaho - Dry pattern west of the Divide, occasional thunderstorms east of the Divide
• Oregon & Washington - A few showers/thunderstorms on Friday, then drying out & warming up.
• California/Nevada - Dry pattern with warmer temps from Sunday on. Tahoe area will see smoke from time to time due to the Electra Fire. 

Synopsis:

A trough of low pressure is located off of the West Coast and a series of disturbances moving downstream of the trough will continue to produce strong to severe thunderstorms across the Northern Rockies with lighter/more spotty showers for the Pacific Northwest.

Meanwhile, a ridge of high pressure will strengthen over the Southern and Central Rockies heading into the weekend, resulting in the hottest temperatures of the summer so far for many areas. Drier conditions will take hold initially across the Southwest and Southern Rockies on Friday, then monsoonal moisture will gradually increase this weekend and into next week.

The hottest temperatures associated with the building dome of high pressure can be expected across the Rockies from Friday through Sunday. The heat will then expand westward toward the West Coast on Monday and Tuesday while the Central and Eastern Rockies will see a slight cooldown. 

Fire and Smoke Update

Thankfully, fire activity is relatively light across much of the West right now. However, the Electra Fire is burning in the Sierra Nevada Range west of Tahoe, and although firefighters are making good progress on getting this fire under control, the Tahoe area will still see smoky conditions at times on Friday and over the weekend.

Forecast for Friday:

An upper air disturbance tracking across the Northern Rockies in combination with ample moisture will result in another active day of thunderstorms across Montana and Northern Idaho, with more isolated and lighter showers/thunderstorms across the Cascades and Blue/Wallowa Mountains.

Further south, thunderstorm coverage will be more isolated along and east of the Divide in Wyoming and Colorado compared to recent days, with mostly dry conditions expected west of the Divide. The focus of moisture will shift southward a bit, though, with an uptick in thunderstorm activity expected across New Mexico.

Thunderstorms across Montana and Northern Idaho will once again have the potential to become strong to severe with hail of 1" in diameter or greater, wind gusts in excess of 60 mph, frequent cloud-to-ground lightning, and heavy rainfall possible. Isolated flash flooding is also a possibility in areas of steep terrain with poor drainage.

Forecast for Saturday:

Another round of thunderstorms can be expected across Idaho and Montana as yet another disturbance moves through, with more isolated coverage further west across Oregon. Storms will have the potential to become strong to severe once again, though the threat looks a bit lower compared to recent days. 

Across the Southern Rockies, thunderstorm activity will be most widespread across New Mexico with only isolated coverage for Southern Colorado and Eastern Arizona.

Forecast for Sunday:

It's been an active week across Montana, but the final in a series of disturbances will move across the state on Sunday with thunderstorm activity mainly confined to southern and eastern portions of the state. Meanwhile, a cold front will move across the high plains with thunderstorms also possible along and east of the Divide in Wyoming and Colorado.

Further south, monsoonal moisture will be on the increase with thunderstorm chances (along with the potential for flash flooding) returning to Arizona and Utah, with an uptick expected across Western Colorado as well.

Outlook for Monday to Tuesday:

Confidence is relatively low regarding the primary flow of monsoonal moisture early next week. Right now, New Mexico and Colorado are expected to see the deepest moisture and highest thunderstorm chances, but Arizona and Utah should see some action as well with an outside chance of moisture reaching as far west as the Sierra.

Meanwhile, a cold front slipping into Eastern Colorado and New Mexico could act as a focal point for thunderstorm activity along and east of the Continental Divide, with locally heavy rain possible along with a welcome break from the heat.

Outlook for Wednesday (7/13) to Thursday (7/14):

Monsoonal moisture is expected to increase across much of the West during this time with an uptick in thunderstorm activity likely across the Four Corners states. Also, moisture is likely to extend northward into Idaho, Wyoming, and Southwest Montana, resulting in isolated to scattered thunderstorms, while the Great Basin and Sierra Nevada Range could get in on the action as well.

Temperatures will remain very hot across most of the West during this period with the core of the heat extending eastward again into the Rockies. However, heavier cloud cover associated with the uptick in monsoonal moisture could limit high temperatures in some areas.

Outlook for Friday (7/15) to Friday (7/22):

Hotter than average temperatures will prevail for most of the West during this period, with the exceptions being coastal regions of the Pacific Northwest as well as Arizona/New Mexico, the latter of which will see some moderation due to the monsoon.

An active monsoonal pattern will continue across the Four Corners region with the core of the moisture possibly shifting into Arizona, Southern Utah, and Southwest Colorado. Flash flood potential will be on the increase as a result. Moisture could also work its way into Wyoming, Idaho, Montana, Nevada, and California at times with a drier pattern prevailing across the Pacific Northwest.

Thanks so much for reading and have a great weekend! Next update on Monday (7/11).

ALAN SMITH