Big Picture Weather Pattern:

The North American Monsoon will recharge this weekend with moisture increasing across the Southwest, Sierra, and Rockies. The result will be an uptick in thunderstorm activity, with storms capable of producing frequent lightning, heavy downpours, and gusty winds. 

5-Day Temperature Outlook:

Temperatures will remain above average throughout the West, though most areas will see a gradual cooling trend by early next week as moisture increases. The exception will be the Pacific Northwest where temperatures will be well above average. 

Wildfire Smoke Outlook:

Large fires continue to burn across the Far Western U.S. and winds blowing from the south/southwest will favor smoky conditions across the Interior Northwest, as well as portion of California. Light smoke and general haziness will be possible at times throughout the West. 

Also, several fires are burning in the lower foothills of Colorado just west of Boulder and Denver, and this will result in smoky conditions and poor air quality in the vicinity of the Front Range.

High-Res Smoke (Sky) Forecast for 5pm Friday:

High-Res Smoke (Sky) Forecast for Noon Saturday:

Air Quality Forecast for 3pm Sunday:

Rain and Thunderstorm Forecast for Fri (Aug 2) to Sun (Aug 4):

Thunderstorm activity will be on the rise throughout the West as monsoonal moisture spreads northward over the weekend. Heavy downpours are possible across the Southwest, while the Northwest could see some dry thunderstorms, resulting in elevated fire danger (and possible erratic fire behavior with ongoing fires).

Let's take a look at the forecast by region...

Colorado:

Thunderstorm chances will ramp up from south to north over the course of the weekend, with the San Juans and Southern Sangres expected to see the most numerous storms and heaviest rainfall amounts. 

Here is our 5-day forecast for Mt. Wilson in the San Juan Range with an hourly precipitation and lightning forecast for Sunday:

Utah:

An uptick in thunderstorm coverage is expected across Southern and Northern Utah, with Sunday expected to be the most active day. Slot canyons, dry washes, and small streams in Southern Utah will see a risk of flash flooding. 

Here are the Flash Flood Ratings for Southern Utah (courtesy of NWS Salt Lake City) for Friday and Saturday, with a further uptick in flash flood potential expected on Sunday.

Sierra Nevada Range:

Friday will be the most active day with thunderstorms favoring the High Sierra, while the Tahoe area should also see some storms. Locally heavy rain will be possible with thunderstorms.

Thunderstorm chances will remain on Saturday and Sunday, but storm coverage will gradually decrease compared to Friday with more isolated activity expected.

Arizona:

Thunderstorm activity will favor Central and Northern Arizona, including the Grand Canyon, Flagstaff region, Prescott, and the Mogollon Rim. Locally heavy rain and isolated flash flooding are possible.

New Mexico:

Thunderstorm activity will favor northern and western portions of the state, including the Sangres and Taos region, while the Ruidoso area will likely see some storms as well.

Northern Rockies:

Friday is looking dry followed by a few isolated thunderstorms on Saturday. On Sunday, more significant moisture will arrive with widely scattered thunderstorms.

Rainfall will be spotty in most areas, but more significant moisture from the plains will reach Central Montana, favoring easternmost ranges such as the Big and Little Belt Ranges where heavy rain is possible.

Forecast for Mon (Aug 5) to Tue (Aug 6):

Monsoonal moisture will remain in place over the Rockies with a drying trend expected for the Sierra. Southwest Colorado and Northern New Mexico, including the San Juans and Sangre de Christos, are favored for the heaviest rainfall.

North of the border, significant rainfall is also possible in the Canadian Rockies, which should help with the wildfire situation.

Forecast for Wed (Aug 7) to Thu (Aug 8):

There will be two focus areas during this period. First, monsoonal moisture will increase across the Southwest, resulting in an uptick in thunderstorm coverage along with a better chance of heavy rain in Colorado, Arizona, and Southern Utah. However, New Mexico will likely see a drying trend.

Further north, a series of disturbances will result in an active thunderstorm pattern over the easternmost ranges of the Northern Rockies, from the Canadian Rockies to Glacier to the Bighorns in Northern Wyoming.

Outlook for Fri (Aug 9) to Tue (Aug 13):

The monsoon will continue to ramp up heading into this period, resulting in an active pattern across the Southwest and the Rockies with frequent thunderstorms along with the potential for locally heavy rain. The Northern Rockies, including Canada, will also see continued shower and thunderstorm chances with beneficial rainfall possible. 

Temperatures will cool off to near or below-average levels across the Rockies, while California will be near to slightly above average. The Northwest will hang onto above-average temperatures. 

Thanks so much for reading and have a great weekend! Next update on Monday (August 5).

Alan Smith