Big Picture Weather Pattern:

A trough of low pressure will slowly work its way across the Pacific Northwest and Northern Rockies, which will help to take the edge off of the heat. Monsoonal moisture will also increase across the Great Basin and Rockies, leading to an uptick in thunderstorm activity with locally heavy rain possible.

Fire danger will be a greater concern across the Interior Northwest due to the potential for dry thunderstorms, while winds will also become gusty across this region, which will be located just south of the jet stream.

5-Day Temperature Outlook:

Most areas are going to see at least some temporary relief from the heat in response to the trough moving across the West. The Pacific Northwest will see below-average temperatures, while the Rockies will stay hot over the next couple of days before cooling off this weekend. 

Fire and Smoke Outlook:

Nearly all areas except for parts of the West Coast and the Far Southwest U.S. have been impacted by smoke this week. Most of the smoke is coming from wildfires burning across the Pacific Northwest and Northern Canada.

Air Quality Ratings on early Wednesday AM:

Wednesday:

Winds blowing from the west/southwest to southwest will continue to favor significant smoke transport across the Interior Northwest and Northern Rockies, while smoke from Northern Canada wildfires will continue to impact Colorado.

We also need to keep an eye on the Gold Complex Fire north of Lake Tahoe, which was triggered by lightning on Monday and has been growing quickly. If this fire continues to grow, then it could add to the smoke issues across the Interior West as well.

Smoke (Sky) Projection for Wednesday afternoon:

Significant fire danger is expected across the Interior Northwest and Northern Rockies on Wednesday due to a heightened potential for dry lightning along with gusty winds. This weather pattern could also fuel the spread of ongoing fires.

Thursday:

More of the same is expected with smoke transport on Thursday as the low pressure trough slowly works its way into the Pacific Northwest. A stubborn northerly flow over Eastern Colorado will continue to reinforce lingering smoke, while Western Colorado should start to see some relief.

Fire weather concerns will persist across the Interior Northwest and Northern Rockies on Thursday due to the threat of dry thunderstorms and gusty winds.

Friday:

A strong west/southwest flow will continue for most of the West, including the Front Range of Colorado which should finally see some smoke relief. 

There is a greater amount of uncertainty for Friday and beyond, however. On the one hand, cooler temperatures could help fire fighting efforts, but if new fires flare up on Wednesday and Thursday, then the situation could look a lot different.

Rain and Thunderstorm Forecast for Wed (Jul 24) to Thu (Jul 25):

Monsoonal moisture will increase throughout the Interior West, resulting in an uptick in thunderstorms from west to east. The North Cascades in Washington along with Southern BC could also see some light showers for the first time in a good while.  

Sierra Nevada Range:

Numerous thunderstorms are expected across the Sierra on Wednesday with locally heavy rain possible. Dry thunderstorms are possible across Northern California (mainly north of Tahoe). On Thursday, moisture will be on the decrease with more isolated thunderstorm activity expected.

Utah:

Scattered thunderstorms can also be expected throughout Utah, especially on Thursday, with locally heavy rain possible. There will be an increased threat of flash flooding in slot canyons, dry washes, and small streams in Southern Utah.

Arizona:

Scattered thunderstorms will favor the higher terrain of Arizona on both days, with Thursday looking slightly wetter than Wednesday. Heavy downpours will be possible with storms, along with a threat of flash flooding in slot canyons, dry washes, and small streams.

New Mexico:

The big surge in moisture will occur here later in the week, but scattered terrain-driven thunderstorms can still be expected on both Wednesday and Thursday with locally heavy rain possible.

Colorado:

A more run-of-the-mill thunderstorm pattern is expected with more significant moisture holding off until later in the week. Most of the action on Wednesday-Thursday will occur west of the Divide, with the San Juan Range looking most favored.

Northern Rockies:

Scattered dry thunderstorms can be expected on Wednesday, with more significant moisture arriving on Thursday with a mix of wet and dry thunderstorms. Western Wyoming, Southwest Montana, and Eastern Idaho will have the best chance of seeing meaningful rain on Thursday, with a greater risk of dry lightning and new fire starts further north.

Forecast for Fri (Jul 26) to Sat (Jul 27):

Moisture will shift eastward late in the week with a drying trend across the Sierra, while New Mexico, Colorado, Wyoming, and SW Montana will see more numerous thunderstorms with locally heavy rain possible.

Utah and Arizona will also hang onto thunderstorm chances, but coverage will become more isolated as drier air begins to work its way in from the west.

Forecast for Sun (Jul 28) to Mon (Jul 29):

As the trough slowly moves across the Interior West, much drier air will arrive from the west as monsoonal moisture makes a significant retreat southward. 

As a result, thunderstorm activity will shut down across most of the West, except for Southern Arizona where monsoonal moisture will begin to rebuild. 

Also, the Pacific Northwest could see some light showers arrive, mainly across the North Cascades and Olympics in Washington.

Outlook for Tue (Jul 30) to Sat (Aug 3):

A ridge of high pressure will build over the Rockies during this period and temperatures will heat back up across this region. The highest temperature anomalies are expected on the east side of the Continental Divide.

Monsoonal moisture will slowly begin to build back into the Four Corners region with an uptick in thunderstorm chances from south to north over time. However, the northern extent of moisture looks to be around the Colorado/Wyoming border at this time. 

The West Coast will hang onto cooler or at least seasonal temperatures during this time, with only slightly above-average temperatures for the Interior Northwest (as opposed to extreme heat in recent weeks). Also, the North Cascades could see some rain showers early in this period, with better chances of rain north of the border in BC.

Thanks so much for reading! Next update on Friday (July 26).

Alan Smith