Big Picture Weather Pattern:

A tall ridge of high pressure will build over the West Coast, resulting in well above-average temperatures for early September. This hot and dry pattern will exacerbate fire activity over the Interior Northwest and more areas will deal with smoke compared to recent weeks.

A cold front will move across the Central Rockies on Wednesday and Thursday, and moisture and energy behind the front will contribute to showers and thunderstorms across Wyoming, Colorado, and New Mexico with Colorado seeing the most widespread action. 

5-Day Temperature Outlook:

Temperatures will be well above average for early September across the Far West, and especially over the Pacific Northwest. Temperatures will be closer to average overall across the Central and Southern Rockies, with the 5-day stretch starting cooler initially and trending warmer this weekend. 

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

Showers and thunderstorms will favor Wyoming initially on Wednesday with most of the action spreading further south into Colorado and New Mexico with the passage of a cold front from Wednesday afternoon into Thursday.

Colorado:

Showers and thunderstorms will develop on Wednesday afternoon and continue through Thursday afternoon, before drying out on Thursday night. Storms on Wednesday afternoon could be on the stronger side, with frequent lightning, hail, gusty winds, and heavy downpours possible.

Northern portions of the state and areas along/east of the Continental Divide will be favored for the most widespread thunderstorm activity and heaviest amounts, with comparatively ower coverage over the San Juans.

Also, higher peaks above 13,000 feet could get dusted with snow. 

New Mexico:

Mostly dry conditions will prevail on Wednesday other than some very isolated thunderstorm activity for northern parts of the state.

Numerous showers and thunderstorms will develop over Central and Eastern New Mexico from Thursday afternoon into Thursday night, with the Sangre de Christo Range (including Taos) and adjacent plains to the east seeing the highest rainfall totals. Western portions of New Mexico will see only isolated activity at most. 

Forecast for Fri (Sep 6) to Sat (Sep 7):

A weak trough of low pressure will move into the Western U.S. with just enough moisture and instability to result in isolated showers and thunderstorms (mainly in the afternoon hours) from the Sierra and Southern Cascades into the Central and Southern Rockies. 

Forecast for Sun (Sep 8) to Mon (Sep 9):

As the trough moves inland, monsoonal moisture will increase across the Interior West with scattered thunderstorms developing across the Four Corners states with more isolated coverage across the Northern Rockies. A few isolated showers/storms are also possible over the Cascades. 

Wildfire and Smoke Outlook:

Hot and dry conditions this week have resulted in an uptick in fire activity, with the largest and most active fires currently burning in Oregon, Idaho, and Wyoming. 

Smoke from these fires will drift southward into Northern Utah on Wednesday, and this trend will continue into Thursday and Friday with Colorado likely seeing some smoke as well.

Over the weekend, a shift to southwest winds should push most of the smoke northward out of Utah and Colorado, while Montana and portions of the Interior Northwest may see an increase in smoke.

Also, weather conditions for the rest of this week and into the weekend will not be great for fire behavior. Temperatures will remain hot and relative humidity low, and isolated "dry" thunderstorms (gusty winds with light and spotty rain) in the vicinity of the fires could exacerbate the fires. 

Outlook for Tue (Sep 10) to Sat (Sep 14):

Above-average temperatures will prevail over the Rockies and Interior West next week, with limited moisture resulting in only occasional isolated showers/thunderstorms over the higher terrain.

The pattern will begin to chance along the West Coast as low pressure troughs begin to arrive. This will result in cooler temperatures for the West Coast, and also increasing rainfall potential over the Pacific Northwest – a sign of the changing seasons. 

Rest of September:

Long-range models are favoring a warm and dry September overall across the Interior West, while the Pacific Northwest is expected to be wetter with more frequent low pressure systems arriving. These signals are most pronounced through mid-month, while the second half of September is less certain.

We are getting to the time of year when cool and wet storm systems (including high-elevation snow) are always a possibility as we head into the autumn season, and that will be something to keep an eye on across the Rockies later in the month despite the milder start to the month.

View → August 2024 Review and September Outlook for the Western U.S.

Thank you so much for reading this summer, and I hope you all have a wonderful fall and winter!

Moving forward, stay tuned for winter forecast preview content and occasional Daily Snow posts for some regions over the next 1-2 months. Regular Daily Snow posts will begin for all areas in November. 

Thanks again!

Alan Smith