Big Picture Weather Pattern:

A trough of low pressure will reach the West Coast early this week, and downwind of the trough, a surge of monsoonal moisture will stream northward into the West Central U.S., favoring Northern Arizona, Utah, Western Colorado, Wyoming, and Southwest Montana for showers and thunderstorms with heavy downpours.

A little bit of moisture from the Pacific will sneak into the Far Northern U.S. from the North Cascades to Glacier where lighter showers and thunderstorms are expected.

5-Day Temperature Forecast:

Although there will be day-to-day fluctuations, temperatures will be near to below average across most of the West this week, with well below average temperatures near the West Coast in Oregon and Northern California. This is the largest area of below-average temperature projections we've seen in the West since May.

Fire and Smoke Outlook:

Large wildfires continue to burn across the Northwest. The wind direction will shift to southwesterly early this week (blowing from the southwest) and the heaviest smoke can be expected across the Interior Northwest and Far Northern Rockies with improvement across the Central Rockies.

High-Res Smoke (Sky) Forecast for Monday PM:

A similar smoke transport pattern is expected for much of the week, with some localized and day-to-day fluctuations. It will also be interesting to see how the fires respond to the cooler airmass this week, which could help to temporarily reduce fire intensity and allow firefighters to make more progress, though occasional gusty winds will also have to be monitored. 

Rain and Thunderstorm Forecast for Mon (Aug 12) to Tue (Aug 13):

The Central Rockies (Utah, Colorado, Wyoming, SW Montana) will see the most widespread shower and thunderstorm activity this week, with locally heavy rain along with a good chance of overnight and early morning activity in some areas.

The Cascades and the northernmost ranges of Washington and Idaho will also see some showers and thunderstorms.

Utah:

Numerous showers and thunderstorms can be expected across both Southern and Northern Utah with locally heavy rainfall and the potential for flash flooding. This model is projecting the heaviest rainfall totals to occur over the Southern Wasatch Range. 

Our forecast for Mt. Timpanogos in the Wasatch Range calls for a good chance of showers and thunderstorms on Monday afternoon and evening, followed by a good chance of showers and thunderstorms at any time of the day on Tuesday. The hourly forecast below is for Tuesday.

The risk for flash flooding will remain elevated across Southern Utah, especially in slot canyons, dry washes, and small streams.

Colorado:

An active pattern will also continue in Colorado with scattered to numerous thunderstorms and locally heavy rainfall. Areas along and west of the Divide will be most favored, especially in Northern/Central Colorado from the Front Range to the Flat Tops to the Elks to the Grand Mesa. 

Northern Rockies:

An active pattern can also be expected up north with showers and thunderstorms favoring the Winds and Tetons in Wyoming, and the Madisons and Gallatins in Montana. Scattered showers can also be expected across Central Idaho and Montana with more isolated activity around Glacier.

Arizona:

Northern Arizona will be the most favored in this pattern, though localized downpours will be possible with storms in mountainous terrain throughout the state. 

New Mexico:

Northern and western portions of the state will see the most widespread activity with locally heavy downpours possible. Storm activity will be more isolated in south-central portions of the state, including the Ruidoso area.

Forecast for Wed (Aug 14) to Thu (Aug 15):

Another trough will move across the Northwest and Northern Rockies, resulting in scattered showers and thunderstorms across the Interior Northwest and Northern Rockies.

Northeast Utah and Colorado will also see scattered thunderstorms, but monsoonal moisture will be trending downward across the Southwest with a significant drying trend across Arizona and most of Utah and New Mexico.

Forecast for Fri (Aug 16) to Sat (Aug 17):

Another trough will impact the Northwest with some models indicating a swath of heavy rain developing east of the Cascades, though confidence is low this far out. Light showers are possible in the North Cascades and Olympics.

The Northern Rockies will also see more showers and thunderstorms, while monsoonal moisture will return to Arizona and Utah with an uptick in thunderstorms expected. Colorado should see a lull in the action with only isolated thunderstorms.

Outlook for Sun (Aug 18) to Thu (Aug 22):

Below-average temperatures will continue near the West Coast while the Interior West will see temperatures trending back to above-average values.

The Southwest and the Southern/Central Rockies will see regular thunderstorm chances return as monsoonal moisture streams back into the region, while disturbances tracking across the Northwest will likely bring some showers and thunderstorms to the Cascades and Northern Rockies. 

Longer-range models are projecting the heaviest rainfall over Utah and Colorado during this period. 

Thanks so much for reading! Next update on Wednesday (August 14).

Alan Smith