Big Picture:

Moisture will decrease a bit for most areas on Friday in response to a weak trough exiting the Northern Rockies out onto the plains, with drier air moving into the Rockies from the west. However, monsoon moisture will begin to increase from the south over the weekend with thunderstorm activity gradually picking up across Arizona, New Mexico, and Colorado.

Further north, another trough will be located over the PNW, which will help to keep temperatures on the cooler side for the end of July. There will not be as much moisture with this trough compared to earlier in the week, however, with dry and breezy conditions resulting in elevated fire danger across interior portions of the Northwest.

Fire and Smoke Outlook:

A handful of large fires across the Northwest will continue to result in periods of light smoke across portions of the Inland Northwest and Northern Rockies, with locally heavy smoke near and just downwind of fires. Further north, fire activity has decreased for the time being across BC thanks to recent cooler/wetter weather, and less smoke is expected this weekend as a result.

Further south, fire activity has picked up a bit in recent days across Arizona and Colorado, and this will result in light smoke across the Southwest at times with locally heavy smoke near the fires.

Forecast for Friday:

Isolated to scattered thunderstorms can be expected across the Colorado and New Mexico Rockies as well as Arizona, with most storms producing light to moderate rainfall as the amount of moisture available in the atmosphere will be lower overall.

Further north, a shortwave disturbance moving across the Northern Rockies will result in scattered thunderstorms across Southwest Montana and North Central Wyoming, with stronger storms capable of producing damaging wind gusts. 

Scattered showers and thunderstorms can also be expected north of the border in BC and Alberta.

Forecast for Saturday:

A subtle increase in moisture will result in scattered thunderstorms across the Four Corners states, including Southern Utah who will see an uptick in thunderstorm activity compared to Friday. Generally light to moderate rain is expected with storms, with only an isolated heavy rain threat.

Further north, isolated thunderstorms can also be expected across the Canadian Rockies as well as portions of Montana and Wyoming.

Forecast for Sunday:

Monsoonal moisture will continue to increase across the Four Corners states with scattered thunderstorms expected. Stronger storms will be capable of frequent lightning and heavy rain, with increasing potential for localized flash flooding in slot canyons and dry washes.

Lingering moisture along the eastern slopes of the Divide in Montana and Wyoming will result in a continued threat of isolated afternoon thunderstorms with generally light rain expected. Isolated storms are also possible across Eastern BC and Western Alberta.

Forecast for Monday to Tuesday:

A more significant uptick in monsoonal moisture is expected across the Southwest during this period, resulting in more numerous thunderstorms across Arizona, New Mexico, Utah, Colorado, and Southern Wyoming along with Eastern Nevada. The Sierra Nevada Range will be right on the edge and may only see a few dry thunderstorms at most.

Thunderstorms in this pattern will be capable of frequent lightning, heavy rainfall, and localized flash flooding in vulnerable terrain.

Outlook for Wednesday (August 2) to Sunday (August 6):

Monsoonal moisture will surge into the Central/Northern Rockies during this period, resulting in an uptick in thunderstorm potential across portions of Idaho, Wyoming, and Montana with locally heavy rain possible.

Some of this moisture will likely reach the Inland Northwest up to the Canadian border, resulting in a chance of thunderstorms, though some of these storms could be of the dry variety which would increase the risk of wildfires.

Further south, thunderstorm chances/coverage are expected to decrease a bit across Arizona as the bulk of the moisture will be moving northward during this period. 

Temperatures are expected to be warmer than average during this period across the Desert Southwest and the Pacific Northwest. Near to below-average temperatures are expected from Central California into the Central Rockies, where more abundant moisture and heavier cloud cover are expected.

Thanks so much for reading! Next update on Monday (July 31).

Alan Smith