August 2024 was somewhat milder compared to July with wetter conditions for much of the Pacific Northwest, Colorado Plateau, and Central/Northern Rockies, while temperatures were also closer to seasonal averages.

September is shaping up to be warmer and drier than average across the Interior West, while the Pacific Northwest is expected to be wetter than average.

August 2024 Review

July was a brutally hot month for much of the West, but August was not as bad for many areas. Temperatures were near to slightly above average for the Northwest, Northern Rockies, and most of California, while the Southwest and Southern Rockies ended up well above average. 

Temperatures were hotter to start the month, while the West Coast and Northern Rockies saw some cooler periods in mid to late August. 

In terms of rainfall, August was also a more active month throughout the West compared to July which was very dry for most areas.

The North American Monsoon ramped up during August, with the heaviest rainfall occurring over the Colorado Plateau (Northern Arizona and Southern Utah) and across the Central Rockies from Utah into Colorado. 

Southern portions of the monsoon region, including Southern Arizona and Southern New Mexico, were not as fortunate as rainfall was below average in these regions.

Rainfall was near average in Wyoming and Eastern Idaho, and above average across a large portion of Montana.

The Pacific Northwest also received above-average rainfall in August, which was good news as this area was the hot spot for wildfires in July. Northern California also received impressive rainfall in late August, mostly from an unusually powerful low pressure system for this time of year.

This late August system even brought snow to many higher-elevation regions in the West, including the Sierra Nevada Range with ski resorts around Tahoe getting dusted with snow for the first time in August in 20 years. 

September 2024 Outlook

High pressure is expected to dominate the weather pattern across the Interior West for much of September, with high confidence of above-average temperatures across the Rockies, Southwest, Great Basin, and Interior Northwest.

There are equal chances for above or below-average temperatures near the West Coast, as low pressure troughs are expected to reach the coast with greater regularity, before weakening inland. 

Precipitation is also expected to be below average across the Southwest and the Rockies as the monsoon already appears to be weakening for the season.

Above-average precipitation is favored across the Pacific Northwest along and west of the Cascade crest as low pressure systems reach this area with more regularity.

September is often a wonderful month for outdoor recreation when temperatures are a little bit cooler, thunderstorm days more intermittent, the leaves start to change, and higher terrain is largely snow-free with only occasional exceptions.

Despite the typical nice weather at this time of year and the balmy outlook for September 2024 (PNW excluded), climatologically speaking, cool and wet storm systems are always possible in September, especially later in the month.

It's also not uncommon for higher-elevation terrain to receive fresh snow in September. New snow at this time of year tends to melt quickly except on north-facing slopes of the highest peaks, but can impact hiking and climbing conditions during and immediately after storms. 

For September 2024, confidence is highest in the warm and dry pattern (for all areas but the PNW) for the first half of the month, but don't be shocked if we see one or more cool/wet systems track across the Interior West during the second half of the month.

Fire and Smoke Outlook

During August, we saw a reduction in fire intensity and smoke transport from Pacific Northwest wildfires, while fire activity flared up significantly across Western and Central Idaho where hotter and drier weather prevailed.

During September, the warm and dry outlook will favor above-normal significant wildland fire potential across portions of the Northern Rockies, Great Basin, and California, while the Pacific Northwest, Colorado, and New Mexico are expected to see "normal" potential. 

Thanks so much for reading!

I will post the next monthly update in early October, and also, stay tuned for winter forecast preview content as ski season approaches.

Alan Smith