Big Picture:

An area of low pressure will continue its gradual trek northward and will continue to strengthen and slow down in speed as it reaches the Northern Rockies.

This low is transporting an abundance of moisture into Northern Utah, Eastern Idaho, Western Wyoming, and Southern Montana, all of which will see the most rainfall from Wednesday through Friday. The Front Range of Colorado will stay in a wet and active pattern as well.

Meanwhile, the bulk of the monsoon will become displaced well northward of its typical home in the Southwest U.S., resulting in a drying trend across Arizona and the Four Corners region, as well as Colorado's San Juan Range, by late this week. 

The area of low pressure along with significant cloud cover will result in below-average temperatures across the Great Basin and Central Rockies during the second half of this week. Above-average warmth will return to the Southwest as moisture and cloud cover decrease. 

Fire and Smoke Outlook:

The main focus of fire activity is across the Interior Northwest where several large fires are burning in North Central Idaho and Northwest Montana. Fires also continue to burn across interior portions of British Columbia as well as Western Oregon, with less fire activity in Washington.

Varying levels of light to moderate smoke can be expected across portions of the Northwest and Northern Rockies during the second half of this week, with locally heavy smoke immediately downwind of the larger fires.

Forecast for Wednesday:

Showers and thunderstorms will be numerous across portions of Eastern Nevada, Utah, Eastern Idaho, Western Wyoming, Southwest Montana, and the Northern Front Range of Colorado. All of these areas will see an increased threat of heavy rainfall with localized flash flooding also possible near small streams and in areas of steep/rocky terrain with poor drainage.

Some of the wetter areas may not see much lightning activity due to cooler temperatures, heavy cloud cover, and reduced instability.

Further south, scattered thunderstorms can be expected across Arizona and New Mexico with a reduced threat of heavy rain, though a low risk of slot canyon flash flooding will remain in place. Isolated thunderstorms are also possible further west into the Sierra Nevada Range.

Forecast for Thursday:

The focus of moisture will lift northward and eastward just a little bit with significant rainfall expected across Northern Utah, Eastern Idaho, Wyoming, and Southern Montana. The potential for isolated flash flooding will exist in all of these areas as well.

Thunderstorms will become more scattered in nature across Nevada, Southern Utah, Colorado, and New Mexico while little to no thunderstorm activity is expected in Arizona.

A little bit of moisture will also sneak into the Northwest with scattered thunderstorms expected across Central and Eastern Oregon. Thunderstorms in this area may produce significant lightning with only light and spotty rainfall, which could result in an uptick in wildfire potential.

Forecast for Friday:

Showers and thunderstorms can be expected across Idaho, Montana, and Wyoming with locally heavy rain possible, though overall rainfall looks lighter compared to prior days. However, confidence is lower for Southern Montana as some models are projecting heavy rain to fall further west in Montana rather than eastward over the plains (which is what this model is depicting).

An uptick in showers and thunderstorms can also be expected across Western Idaho and Oregon with locally heavy rain possible in some areas such as the Wallowa Range, while a mix of wet and dry thunderstorms are expected further west in the Cascades. A few isolated storms are also possible in Washington.

Further south, a drying trend is expected across Utah and Colorado while Arizona and New Mexico are also looking dry. 

Forecast for Saturday to Sunday:

A trough of low pressure will move across the Pacific Northwest and Northern Rockies over the weekend, which will interact with lingering monsoonal moisture to result in more showers and thunderstorms across the Northern U.S. Rockies as well as the Canadian Rockies. Storms will be faster-moving but locally heavy rain will remain possible along with frequent lightning.

Pacific moisture will also reach the Cascades with light showers expected. Further south, a little bit of moisture will sneak back into Utah and Colorado with thunderstorm chances favoring the northern halves of these states. The Colorado Front Range could also see a more noticeable uptick in thunderstorm activity.

A strong jet stream (by August standards) will set up across the Central Rockies during this period. This will result in gusty winds across the higher peaks of Utah and Colorado, and will also suppress deeper monsoonal moisture over the Southwest well south of the Mexico border, resulting in dry conditions across Arizona and New Mexico.

Outlook for Monday (Aug 7) to Friday (Aug 11):

Additional disturbances will move across the Northwest and Northern Rockies during this period, interacting with lingering monsoonal moisture to result in frequent shower and thunderstorm activity across the Northern Rockies – though likely to a lesser extent compared to prior days.

Pacific moisture reaching the West Coast with these disturbances will also result in occasional shower chances across the Cascades.

Further south, the monsoon will remain in a weakened state with limited thunderstorm activity across the Southwest thanks to a strong jet stream over the Central Rockies. Isolated thunderstorm chances may eventually sneak back into the picture as the week progresses, however.

Temperatures are expected to remain cooler than average during this period across the Central and Northern Rockies, while the Southwest is expected to see hotter-than-average temperatures. 

Thanks so much for reading! Next update on Friday (August 4).

Alan Smith