Big Picture Weather Pattern:

A strong ridge of high pressure will set up over the West Coast late this week, signaling the start of a brutal heat wave that will eventually impact nearly the entire Western U.S. 

Northwest winds aloft on the east side of the ridge will bring much drier air into the Southwest with monsoonal moisture retreating south of the Mexico border. Areas east of the Continental Divide will hold onto cooler temperatures and higher moisture levels, resulting in continued thunderstorm chances. 

Over the next 7 days, the worst of the heat will be over the West Coast states with temperatures running well above average. Areas east of the Continental Divide will see cooler temperatures through Friday or Saturday, before the warmer airmass eventually starts to spread east next week.

California will experience severe heat with triple digits in the Central Valley, and even higher-elevation towns in the Sierra will see highs in the 80s and 90s. 

The heat will also spread northward into the Pacific Northwest. Check out our forecasts for Portland and Bend. Triple-digit heat is likely in Portland this weekend, and Bend will see highs getting very close to the century mark as well. 

5-Day Precipitation Forecast:

A significant drying trend will occur west of the Divide during this pattern as monsoonal moisture retreats south of the Mexico border. Areas along and east of the Divide will have the best chance of seeing thunderstorms and measurable rain. 

Fire Danger:

Unfortunately, a severe heat wave accompanied by dry air and low relative humidity will lead to a rise in fire danger. There are already a few large fires burning in the lower foothills of the Sierra and the potential for new fires will expand over time across much of the West.

Be sure to use the following tools to track wildfires and smoke:

• Active Fires Map
• Real-Time Air Quality Map
• Smoke High-Res (Surface) Map

Forecast for Wed (Jul 3) to Thu (Jul 4):

An active pattern will persist for the east side of the Divide in the Northern Rockies, with a good chance of showers and thunderstorms for areas such as Glacier, the Beartooths, the Bighorns, and the eastern/northern sides of Yellowstone.

To the south, isolated storms are possible over the eastern ranges of Colorado and Northern New Mexico, but better chances will exist further east on the plains.

Here is a zoomed-in rainfall projection for the Northern Rockies, with the easternmost ranges being the most favored for rain and thunderstorms. 

Forecast for Fri (Jul 5) to Sat (Jul 6):

Lingering moisture will result in isolated thunderstorm chances on the eastern side of the Divide in the Northern Rockies. The Southern Rockies will also see some isolated storm chances along and east of the Divide, especially in Southern Colorado and New Mexico.

Forecast for Sun (Jul 7) to Mon (Jul 8):

Even the eastern slopes of the Divide will see a drying trend as the strong high pressure ridge works its way from the West Coast into the Intermountain West. Some isolated thunderstorm activity can still be expected along and east of the Divide from Wyoming into Northern New Mexico.

Outlook for Tue (Jul 9) to Sat (Jul 13):

A heat wave will continue to impact the West with the core of the heat gradually shifting eastward over time. Most areas will see little to no rain during this period, with only southern/central portions of Arizona and New Mexico seeing a gradual increase in thunderstorm chances by later in the period as monsoonal moisture begins to work its way back in from the south.

Thanks so much for reading and Happy Fourth of July! Next update on Monday (July 8).

Alan Smith