Big Picture Weather Pattern:

A trough of low pressure moving across the Northern Rockies will lead to an active start to the week in Montana, Wyoming, and Canada.

Lingering monsoon moisture in Colorado will lead to more t-storms on Monday, with a focus shifting into Southern New Mexico and Arizona mid-week as the jet stream moves across the Rockies, which will act to suppress moisture further to the south.

A strong ridge of high pressure is currently building just off the West Coast and will move into California over the coming days, signaling the start of a heat wave with well-above-average temperatures.

Below are the projected temperature anomalies over the next 5 days. The Intermountain West will actually see some cooler temperatures (relative to average for early July) with a northwest flow pattern setting up (winds blowing from the northwest), while California will heat up significantly. 

5-Day Precipitation Forecast:

Rainfall over the next 5 days will favor the Northern Rockies and portions of the Southwest. Utah and points west will see drier conditions, and the Pacific Northwest will also see a notable drying trend. 

Forecast for Mon (Jul 1) to Tue (Jul 2):

Monday will be the most active day with numerous thunderstorms across the Northern Rockies and Southern Rockies. On Tuesday, we'll hang onto scattered showers and thunderstorms across the Northern Rockies, while Colorado will see fewer thunderstorms with deeper moisture becoming confined further south into Arizona and New Mexico.

Colorado:

The San Juans will be the most favored area for thunderstorms in this pattern with more isolated activity over the Front Range.

New Mexico:

There is a good chance of storms for all areas but the eastern plains and southern deserts. Northern and western portions of the state will be most favored. Burn scars and dry washes will continue to see a flash flooding threat.

Arizona:

The Mogollon Rim will be the most favored in this pattern with locally heavy rain and flash flooding possible. The edge of the monsoon moisture will also extend into the Flagstaff and Tucson areas with thunderstorms possible. Drier conditions are expected for the Grand Canyon and points west and north.

Northern Rockies:

The two most favored areas for rain and thunderstorms include the Northern Montana/Canada border region around Glacier and Whitefish, and the Southern Montana/Wyoming border region including Yellowstone, the Beartooths, and the Bighorns. 

Here is the hourly rain and lightning forecast for Old Faithful on Monday, which is expected to be the most active day this week.

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

A northwest flow pattern will set up heading into the Fourth of July. This will result in a continued active pattern across the Northern Rockies, mainly along and east of the Divide with showers and thunderstorms along with cooler temperatures.

The northwest winds aloft will bring drier air to areas west of the Divide, and this will also help to scour out monsoonal moisture across Colorado. Areas east of the Divide in Colorado will hang onto isolated storm chances, with a notable reduction in activity west of the Divide.

Thunderstorm activity will also decrease across Arizona and New Mexico relative to prior days, but isolated terrain-driven storms can still be expected.

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

The pattern looks quiet for most of the west as we finish out the week. A drying trend is expected across the Northern Rockies, while limited monsoon moisture will keep the best chance of storms confined to Southern New Mexico and SE Arizona. Some of this moisture may also creep back into Southern Colorado, but confidence is low.

Outlook for Sun (Jul 7) to Thu (Jul 11):

Get ready for some serious summer heat with above-average temperatures expected throughout the West.  A ridge of high pressure will remain over the West Coast early in the week with the heat even extending northward into the Pacific Northwest.

The location of the high pressure center far to the west over the Great Basin will keep most of the monsoon moisture suppressed south of the Mexico border, with a dry pattern expected for most areas. We may see a little bit of moisture creep into southern/western portions of the Southwest, especially by later in the period.

Also, the northwest flow aloft pattern east of the Divide can support low-level moisture transport toward the eastern slopes (from the plains and Gulf of Mexico) at times, so we could see some occasional thunderstorm chances pop up over the easternmost ranges of the Rockies.

Heading into mid-month, long-range models are in decent agreement that high pressure will shift eastward over time, which should open the door back up to monsoonal moisture returning to the Four Corners region from the south. 

Thanks so much for reading! Next update on Wednesday (July 3).

Alan Smith