Big Picture:

Monsoonal moisture is returning to the Southwest this week. The northward push of moisture will be aided by an area of low pressure near the California Coast, with counterclockwise (cyclonic) winds helping to draw this moisture into the Sierra, Utah, and Western Colorado by late in the week.

This is not an overly robust monsoon moisture surge by seasonal standards, but it will still result in a noticeable uptick in thunderstorm coverage compared to recent weeks and isolated flash flood potential will return to slot canyons and dry washes.

Also, hikers and climbers from the Sierra to the Colorado Rockies should be aware of increased lightning risk during the second half of this week.

Further north, the Northwest and Northern Rockies will remain unsettled on Wednesday and Thursday as a trough moves across the area. These areas will start to dry out late this week following an extended stretch of active weather.

Temperatures will remain below average across most of the West through Friday before trending warmer this weekend. A ridge of high pressure will build along the West Coast this weekend, resulting in warmer-than-average temperatures by Sunday.

Fire and Smoke Outlook:

From a broader perspective, fire activity remains fairly isolated across the West thanks in part to recent active weather along with cooler temperatures. There has been an uptick in fires across Southern Utah and Southern Colorado in recent days, though, due to dry and breezy conditions.

Overall, smoke transport is low across the West right now, and generally confined to areas near the fires.

Forecast for Wednesday:

Scattered to numerous showers and thunderstorms can be expected across Northern Arizona with locally heavy rain possible under stronger storms. Some isolated thunderstorm activity is also expected in the SoCal Mountains. The rest of the Four Corners will be mostly dry as the moisture will not quite reach these areas yet.

A trough moving across the Northwest will result in showers across the Olympics and Cascades in Washington with scattered showers and thunderstorms across the Inland Northwest and Northern U.S. Rockies. Showers and thunderstorms will be more widespread across BC with heavier rainfall also expected.

Forecast for Thursday:

Another active day of thunderstorms is expected across Northern Arizona. Thunderstorm activity will also increase across the SoCal Mountains, Southern Sierra Nevada Range, Southern Nevada, Utah, and Southwest & Western Colorado.

Northern areas will see a drying trend overall, but there will be enough lingering moisture and instability for some isolated showers and thunderstorms across the Cascades, Western Canada, and Northern U.S. Rockies.

Forecast for Friday:

Monsoonal moisture will lift northward a bit with thunderstorm activity favoring the Central Sierra Nevada Range, Central Nevada, Utah, and Western/Central Colorado. Storms will be more isolated further south across Arizona and New Mexico.

A significant drying trend can also be expected across the Northwest and Northern Rockies. Shower chances will be higher further north across Central BC & Alberta as another storm system arrives from the Pacific.

Forecast for Saturday to Sunday:

Scattered afternoon showers and thunderstorms can be expected both days across the Four Corners states with parts of Wyoming getting in on the action as well. Also, a more noticeable uptick and northward trend in thunderstorm activity is expected across the Sierra Nevada Range including Tahoe.

Outlook for Monday (Aug 14) to Friday (Aug 18):

Monsoonal moisture will decrease across the Southwest during this period, and a trough of low pressure moving into Montana and Wyoming may be a factor in weakening the monsoon circulation temporarily.

However, isolated thunderstorms can still be expected across the Four Corners states, while areas near/east of the Continental Divide in the Northern & Central Rockies may see an uptick in moisture and storm chances at some point during this period.

Also, lingering moisture may continue to result in a higher likelihood of showers/thunderstorms across the Sierra and Tahoe region early in this period.

A ridge of high pressure setting up over the West Coast will also result in much hotter temperatures across California and the Pacific Northwest next week. The Southwest is also looking hot with above-average temperatures, while near-average temperatures are expected across the Central Rockies. 

Thanks so much for reading! Next update on Friday (August 11).

Alan Smith