Rainfall was above average across a large portion of the West during August with significant fire activity and smoke largely confined to the Pacific Northwest.

Now that we're beyond Labor Day, the rest of September is shaping up to be relatively quiet as we transition into autumn.

While the leaves will begin to turn in many areas later this month, we are also getting to the time of year when we need to keep an eye out for the first fall cold fronts that could bring widespread snow to higher elevation areas. 

August 2023 Review:

August was an active month across the West. The North American Monsoon finally kicked in after a slow start in July, but southwest winds associated with frequent low pressure troughs near the West Coast transported richer moisture northward into the Central and Northern Rockies where rainfall was above average. 

Rainfall ended up below average across Southwest Colorado, New Mexico, and Southern Arizona.

Meanwhile, the tropics also made a visit to the West. Hurricane Hilary tracked from south to north near the Baja Peninsula before reaching Southern California at tropical storm strength – a rare occurrence for California.

Moisture from Hilary brought significant rainfall to California, Nevada, Idaho, Eastern Oregon, Eastern Washington, and Montana. In fact, many areas in Southern California experienced their wettest August on record.

Wildfire activity was most common across Western Oregon and Far NW California. Idaho, Eastern Washington, and Western Montana had active fires earlier in August before heavy rainfall from Hilary arrived. Smoke from these fires as well as those burning in British Columbia impacted the Northwest frequently.

Despite the overall wet pattern, temperatures were above normal across a large portion of the West. The warmest temperatures relative to average occurred across the Southwest and the Northwest, with near to slightly above-average temperatures for most other areas.

September 2023 Outlook:

The first few days of September, which included Labor Day weekend, were wet across much of the West thanks to a powerful low pressure system. The next 1-2 weeks (as of September 5th) should feature calmer conditions in most areas.

For the month as a whole, above-average precipitation is expected across the Pacific Northwest. An area of the Southwest is also noted for above-average precipitation, but this may be partly due to the wet conditions experienced over the first few days of the month.

Most other areas have equal chances of above or below-average precipitation, with the exception being New Mexico and Southern/Eastern Colorado where drier conditions are expected.

Overall, thunderstorm and lightning frequency will be trending downward as the month progresses, as our days will be getting shorter and temperatures cooler. The monsoon has already weakened significantly, though occasional weak influxes of monsoonal moisture will remain possible into the Southwest and parts of the Rockies. 

Temperatures are expected to be warmer than average this month across the Rockies, while areas near the West Coast have equal chances of above or below-average temperatures. Even so, we'll still have to keep an eye out for the first significant cold front(s) of the fall which can arrive in September.

Fire and Smoke Outlook:

Fire activity really picked up across Western Canada and parts of the Northwest during the latter half of August. Fortunately, cool and wet conditions during the first few days of September have significantly reduced fire activity, at least for the time being.

Even though the hottest days of summer are now behind us and we have seen welcome rainfall recently, above-average fire potential is still being forecast this month across the Pacific Northwest. However, it's unlikely that smoke coverage will be as significant compared to the second half of August.

Elsewhere, below-average fire potential is expected across most of California, with near-normal potential expected across the Rockies.  

The good news is that near-normal fire activity is expected across Western Canada this month, thanks to seasonally cooling temperatures along with better rainfall potential.

Hopefully, the worst of what has been a severe fire season in Canada is now behind us, though significant fires are still burning in parts of Northern Canada.

Alan Smith, Meteorologist