The past week was unseasonably cool and wet across the Rockies with significant rain totals, below-average temperatures, and even some high elevation snow. A nice change at the tail end of what has been a very hot and dry summer for many!

Check out the estimated rain totals from the National Weather Service for the one-week period ending on Sunday morning, August 22nd.

We are heading into a much quieter pattern during the final week of August, and the final week of Meteorological Summer (which ends August 31st). Fortunately, the recent rainfall has significantly reduced fire danger across the Rockies. 

Precipitable water – a measure of the amount of water vapor in the atmosphere – is projected to be below average across most of the West on Monday afternoon, except for parts of New Mexico where a weak monsoon persists.

A bigger picture look reveals a storm system near the Canadian border that has produced rain north of the border, but only light and spotty rainfall south of the border. The monsoon has largely become suppressed to the south by recent storm systems. Southern New Mexico and Southeast Arizona are the only areas that will see any noticeable influence from the monsoon early this week.

As we head into the second half of the week, a series of "dry" disturbances will continue across the north, resulting in cool and breezy conditions with limited rain potential. However, a storm system on Thursday will dip a bit farther south and tap into monsoon moisture, resulting in an uptick in thunderstorm potential across Colorado.

Temperatures over the next 5 days will generally be cooler than average across the Northwest and Northern Rockies, warmer than average across the Southwest and Southern Rockies, and right around average in California.

Wildfire and Smoke Update

Large wildfires and heavy smoke continue to impact California. Sadly, particulate matter levels are well above the "Hazardous" level around Tahoe as of midday Monday. 

Strong southwesterly winds aloft are transporting much of this smoke northeast into Nevada, Idaho, Northern Wyoming, and Southern Montana. Farther north, there are a handful of fires burning in the Cascades in Washington and Oregon, resulting in isolated smoky conditions but much less widespread compared to California.

Tuesday's smoke outlook is similar to Monday's, though weaker winds aloft should result in somewhat lighter levels of smoke reaching the Northern Rockies. 

Forecast Smoke (surface)

Forecast Smoke (sky)

Current Air Quality

A similar pattern will remain in place on Wednesday. Then, on Thursday and Friday, winds aloft will transition to west/northwest, shifting the downstream plume of smoke farther south into Utah and Colorado.

Forecast for Monday, August 23rd

Thunderstorm activity will be very isolated at best across most of the Rockies, while the Northern Cascades could also see a few light showers. Southeast Arizona and Southern New Mexico will see the best chance of thunderstorms and wetting rains with monsoonal moisture in place.

Forecast for Tuesday, August 24th

The Central and Northern Rockies are looking almost completely thunderstorm-free on Tuesday, while Arizona and New Mexico will continue to see a better chance of thunderstorms.

Forecast for Wednesday, August 25th

The next Pacific storm system will move into the Northwest on Wednesday but will contain much less moisture compared to last week's storms. A few isolated thunderstorms will be possible across the Central and Northern Rockies, along with some light showers over the Olympics and Northern Cascades. Meanwhile, a decrease in thunderstorm activity is expected across Arizona and New Mexico.

Forecast for Thursday, August 26th

Energy from the approaching storm system will tap into increasing monsoonal moisture from the southwest to result in an uptick in thunderstorm activity across the high country of Colorado, with more isolated activity expected south into New Mexico and northward into Wyoming and Montana.

Shower activity will also pick up across the Central/Northern Cascades and Olympics in Washington with more widespread rain north of the border in British Columbia.

Forecast for Friday, August 27th

Lingering moisture behind Thursday's system will result in more isolated thunderstorms and lighter rain across Colorado and New Mexico on Friday. Meanwhile, another system will impact the Northwest on Friday with light showers for the Cascades and Idaho Panhandle and a better chance of showers and thunderstorms across Montana and north of the border in BC and Alberta. 

Outlook for Sat, Aug 28th - Wed, Sept 1st

Over the weekend, additional disturbances moving across the Northwest will result in shower chances across the Cascades and Northern Rockies. Early to mid next week, a storm system will dip a little farther south, tapping into some more monsoonal moisture to result in better chances for thunderstorms across the Central and Southern Rockies.

Temperatures will also trend warmer across the West during this time. Above-average warmth is projected for most areas, except the Pacific Northwest where near-average temperatures are projected.

Thanks so much for reading! Next update on Wednesday (8/25).

ALAN SMITH

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