Big Picture:

A slow-moving low pressure system along with significant monsoonal moisture will linger over the Northern Rockies on Friday. Moisture will decrease somewhat heading into the weekend, but another trough of low pressure will arrive and will interact with lingering moisture to result in additional showers and thunderstorms across the Northwest and Northern Rockies.

A strong jet stream (by August standards) will also set up from California into the Central Rockies over the weekend. While active weather can be expected on the north side of the jet stream, much drier conditions can be expected south of the jet with stronger westerly winds keeping monsoonal moisture suppressed south of the Mexico border.

The jet stream will also act as a dividing line as far as temperatures go this weekend and early next week. Temperatures will be cooler than average across the Northern Rockies and hotter than average across the Southwest.

Fire and Smoke Update:

Northerly surface winds have developed near the Pacific Coast and will transport smoke from the Flat Fire in SW Oregon into California, with varying levels of smoke and air quality impacts expected through the weekend.

Elsewhere, fires continue to burn across portions of Northern Idaho, NW Montana, and British Columbia, resulting in light smoke across much of the Interior Northwest with locally heavy smoke near and just downwind of fires.

Remnant monsoonal moisture will set up over portions of the Pacific Northwest through this weekend and into early next week, resulting in a mix of wet and dry thunderstorms with the potential for new fires due to lightning.

Forecast for Friday:

Widespread showers and thunderstorms will continue across Central/Eastern Idaho, Western Wyoming, and Southern Montana with locally heavy rain possible. Excessive runoff and flash flooding are also possible on a localized basis in small streams and in areas of steep/rocky terrain with poor drainage.

Scattered to numerous thunderstorms can also be expected across Central and Eastern Oregon and Southern Washington. Some storms will produce heavy downpours, while other storms may only produce light rain but with frequent lightning, resulting in increased fire danger. 

Further south, only isolated thunderstorms are expected across Northern Utah and North/Central Colorado, with drier conditions further south.

Forecast for Saturday:

A trough of low pressure will move into the Northwest on Saturday, resulting in scattered showers and thunderstorms across the Cascades and more numerous showers and thunderstorms across Idaho, Southeast BC, Western Montana, and Western Wyoming. Locally heavy rain will be possible with storms, but the flash flooding threat will be lower compared to prior days.

Mostly dry conditions are expected further south, except for the Northern Colorado Front Range where isolated thunderstorms are possible. 

Forecast for Sunday:

A trough of low pressure will continue to impact the Northwest and Northern Rockies with numerous showers and thunderstorms expected from the Eastern Cascades to the Eastern Rockies of Montana/Wyoming. Frequent lightning and locally heavy rainfall will be possible under stronger storms.

To the south, a slight uptick in thunderstorm coverage is expected across Northern Utah and Northern Colorado, but coverage still looks fairly isolated. 

Forecast for Monday to Tuesday:

Another trough will move across the Northwest and Northern Rockies early next week and will interact with lingering moisture to result in good chances of showers and thunderstorms across the Cascades, BC Interior, and Northern Rockies. 

Isolated thunderstorms will remain possible across the Colorado Front Range, with drier conditions across most of the Southwest. The one exception will be Southern Arizona where isolated thunderstorms are possible as some monsoonal moisture starts to sneak back in from the south.

Outlook for Wednesday (Aug 9) to Sunday (Aug 13):

Frequent disturbances will continue to track across the Northwest and Northern Rockies during this period, resulting in frequent shower and thunderstorm chances though rainfall amounts should be lighter compared to the week prior. 

Monsoonal moisture should gradually start to work its way back into the Four Corners region, but it looks like a weak "push" of moisture with below-average rainfall still expected. 

Temperatures are expected to remain below average across the Northern Rockies during this period with above-average temperatures across the Southwest. Temperatures are also expected to trend warmer than average along the West Coast. 

Thanks so much for reading! Next update on Monday (August 7).

Alan Smith