Big Picture Weather Pattern:

Monsoonal moisture will linger across Colorado and Wyoming on Monday, resulting in a good chance of thunderstorms, while activity will become more isolated in Utah as the best moisture pushes eastward. All areas in the Rockies will see a drying trend on Tuesday with only isolated thunderstorms.

Across the Pacific Northwest, a series of low pressure troughs will continue to bring moisture to the region, resulting in showers across the Olympics, Cascades, and western lowlands. 

5-Day Temperature Forecast:

Temperatures will be well below average near the West Coast this week and near average across the Rockies. Areas east of the Continental Divide and across the Southwest will see above-average temperatures. 

Forecast for Mon (Aug 19) to Tue (Aug 20):

Thunderstorm activity will favor the Central Rockies on Monday with heavy downpours occurring, while Utah and Arizona will see more isolated storms. Idaho and Montana will also see scattered thunderstorms. Storm coverage will be more isolated across the Rockies on Tuesday.

The Olympics, Cascades, and NE Washington ranges will see more showers early this week, with heavy rain on the windward side of the Olympics. 

Colorado:

Good chance of thunderstorms statewide on Monday with locally heavy rain possible, while a downtick in activity is expected on Tuesday with more isolated terrain-based thunderstorms. 

Northern Rockies:

Similar to Colorado, the Northern Rockies will see greater storm coverage on Monday with heavy downpours possible in Western Wyoming and Southwest Montana. More isolated activity with brief/light rain is expected on Tuesday. 

Pacific Northwest:

The Cascades and Puget Sound region will stay mostly dry during the day on Monday, but rain will develop over the Olympic Peninsula by Monday afternoon. Showers can then be expected across the Cascades and NE Washington Ranges on Monday night and Tuesday.

Western and northern portions of the Olympic Peninsula will see significant rainfall amounts in this pattern with lighter amounts for the Cascades. Also, drier conditions are expected in Oregon aside from some isolated showers and thunderstorms. 

Forecast for Wed (Aug 21) to Thu (Aug 22):

The pattern will turn more active thanks to two main weather features:

1) Monsoonal moisture will surge northward from Mexico back into the Southern Rockies, resulting in more numerous thunderstorms across Arizona, Utah, Colorado, and New Mexico with heavy rain possible. Flash flooding potential will increase in slot canyons, dry washes, and burn scars.

2) A fall-like Pacific low pressure system will reach the West Coast, resulting in rain developing across Western Washington, Oregon, and Northern California with scattered showers and thunderstorms for the Interior Northwest. 

Forecast for Fri (Aug 23) to Sat (Aug 24):

The Pacific storm system will move inland with cool air and moisture arriving, though confidence is low at this time on which areas will be more or less favored for rain. For now, it looks like a decent chance of more rain across the Pacific Northwest, with the potential for soaking rains (and even high-elevation snow) across portions of the Northern Rockies.

The Southern Rockies will continue to see a good chance of showers and thunderstorms in this pattern as energy from the Pacific storm system interacts with lingering monsoonal moisture. Cooler air will also reach Utah and Colorado by Saturday. 

Fire and Smoke Outlook:

Cooler temperatures have contributed to a reduction in fire intensity and smoke transport across the Pacific Northwest. Large fires burning in Idaho, Wyoming, and Northeast Washington are the major smoke producers early this week.

Areas located to the northeast of these fires are most likely to experience smoky conditions early this week due to winds blowing from the southwest. 

High-Res Smoke (Sky) Forecast for 7pm Monday:

Outlook for Sun (Aug 25) to Thu (Aug 29):

An overall warming trend back to more seasonal (or slightly above average) temperatures is expected following the weekend cool snap. However, there are some hints of a cold front reaching the Northern Rockies midweek, though could cool things down again briefly while also resulting in a chance of showers and thunderstorms.

A lower-grade monsoon pattern is expected to persist across the Southern Rockies with typical afternoon thunderstorms expected, though no major upticks in storms or rainfall are expected at this time (though that could always change).

Thanks so much for reading! Next update on Wednesday (August 21).

Alan Smith