Big Picture Weather Pattern:

A ridge of high pressure will build over the Western U.S. this weekend, resulting in a significant warm-up for most areas, especially over the Interior Northwest. Mountain valleys could still see chilly mornings though, as the nights are getting longer at this time of year. 

Monsoonal moisture will primarily be located south of the high pressure center of New Mexico, Arizona, and Southern Colorado, resulting in afternoon thunderstorm chances. This will be a weaker monsoon pattern with isolated to scattered activity. 

5-Day Temperature Forecast:

Temperatures will be above average for nearly the entire West over the next 5 days, except for New Mexico where temperatures will be below average. The highest temperature anomalies are expected over the Northwest.

Forecast for Fri (Aug 30) to Sun (Sep 1):

Shower and thunderstorm activity will largely be confined to New Mexico, Arizona, and Southern Colorado. We will also see enough moisture reach Southern Utah, Nevada, and the Sierra in California on Sunday for some isolated thunderstorm chances.

New Mexico:

This will be a scattered afternoon thunderstorm type pattern for most of the state on Friday. A reduction in coverage is expected on Saturday with more isolated activity.

On Sunday, moisture arriving from the Gulf of Mexico will contribute to more numerous showers and thunderstorms across Southern New Mexico (including Ruidoso) while Northern New Mexico looks less active. 

Arizona:

Daily rounds of isolated to scattered thunderstorms can be expected throughout the weekend in both Southern and Northern Arizona. Saturday looks like the most active day with higher coverage, while Friday and Sunday will feature more isolated coverage.

Forecast for Mon (Sep 2) to Tue (Sep 3):

A weak trough of low pressure will move into the Western U.S. on Labor Day, and this will pull moisture northward, resulting in isolated to scattered thunderstorms across the Central and Northern Rockies, as well as the Interior Northwest.

In other words, Monday looks like the one day with appreciable thunderstorm chances of the 3-day holiday weekend across central and northern areas. Thunderstorm chances are also anticipated on Tuesday.

The Southwest will see a drying trend with only some isolated thunderstorm activity. The exception will be far southern New Mexico near the Texas/Mexico borders where more significant moisture will result in a higher potential for rain and thunderstorms. 

Forecast for Wed (Sep 4) to Thu (Sep 5):

Confidence is lower for this period as weather models are in poor agreement on how quickly the weak low pressure trough will exit to the east.

If the trough is slow enough and hangs around, then isolated thunderstorm chances would remain over the Central and Eastern Rockies, at least on Wednesday, with a drying trend likely the further west you go away from the Continental Divide.

Fire and Smoke Outlook:

Large and active wildfires continue to burn in Idaho, and there has been a recent uptick in fire activity in Central California as well.

Smoke from the fires in Idaho has drifted southward into Northern Utah, and this pattern looks to continue through Friday.

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

On Saturday, a shift to southwest winds (blowing from the southwest) will push most of this smoke northward, with clearing conditions in Utah, while West/Southwest Montana will see an uptick in smoke. Most of Southern/Central Idaho looks to stay very smoky throughout the weekend.

High-Res Smoke (Sky) Forecast for 8pm Saturday:

Outlook for Fri (Sep 6) to Tue (Sep 10):

Late summer heat will continue with temperatures running above average for most of the West. A weak monsoon will keep isolated thunderstorm chances going across the Southwest and Southern Rockies (favoring New Mexico and Southern Colorado) with drier conditions further north.

Toward the end of this period, longer-range models are hinting at a trough of low pressure approaching the Pacific Northwest, which could lead to a chance of showers across Western Washington and Oregon. 

Thanks so much for reading and have a wonderful Labor Day weekend!

The next and final post of the season will be on Wednesday, September 4th.

Alan Smith