Forecast Highlights:

• Southern Rockies & Southwest (NM, AZ, CO, Southern Utah) - Daily rounds of thunderstorms for the foreseeable future with frequent lightning and heavy rain.
• Northern Rockies & Great Basin (WY, ID, MT, NV) - Isolated to scattered thunderstorms nearly every day through early next week.
• California - Isolated Sierra thunderstorms Thursday & Sunday. Smoky Northern Sierra due to Washburn Fire.
• Pacific Northwest - Mostly dry pattern with isolated light showers possible for the WA Cascades on Saturday.
• Flash flood risk for slot canyons, dry washes, and burn scars in the Southwest nearly every day.

Synopsis:

A ridge of high pressure will remain in place across the Intermountain West resulting in hot temperatures for many. However, an active monsoonal flow will continue as well, keeping daily rounds of thunderstorms going across the Southern Rockies. In addition, monsoonal moisture will surge northward on Wednesday, resulting in thunderstorms across the Northern Rockies in the days to follow. 

Numerous upper air disturbances associated with a trough of low pressure off the Pacific Coast will move across the Rockies over the next several days, and will act as a "trigger" for thunderstorm development with ample moisture and instability in place. 

The amount of water vapor in the atmosphere will be well above average on Wednesday afternoon (and in the days to follow) throughout the Rockies. This will help to fuel thunderstorms, some of which will produce locally heavy rainfall as well as frequent cloud-to-ground lightning.

Storms will be most common during the afternoon and evening hours, but elevated moisture levels in conjunction with the mentioned upper air disturbances could result in some overnight and early morning storms as well – something to keep in mind if you have peak-bagging plans.

Despite the monsoonal moisture surge, temperatures will remain well above average across most of the West this week. Areas that see the most widespread shower/thunderstorm activity and associated cloud cover could see some moderation of high temperatures on any given day, though.

Looking for more comfortable temperatures without the high elevation lightning danger? Head to the Pacific Northwest, along and west of the Cascade crest, where temperatures will be just about perfect and lightning potential will be close to zero.

Fire and Smoke Update:

The main smoke producer over the next several days will be the Washburn Fire in Yosemite National Park. Fires in Utah will continue to burn, but with abundant monsoonal moisture arriving, fire behavior and significant smoke transport is expected to be reduced compared to prior days.

The heaviest smoke over the coming days will be near and north/northeast of the Washburn Fire in the Sierra, and in the immediate vicinity of the Utah fires. Otherwise, light amounts of smoke and haze are projected from time to time elsewhere across the Rockies and Great Basin but should not significantly impact air quality (assuming no new fire starts, of course).

We'll have to keep an eye on new fire starts this week due to the amount of lightning expected. On the plus side, the amount of monsoonal moisture will be significant for most areas, even in the Northern Rockies, to prevent widespread dry lightning outbreaks. If there is one area where dry lightning could be a more significant concern, it would be the Sierra on Thursday and Sunday.

Forecast for Wednesday:

Scattered thunderstorms can be expected throughout the Rockies and Canyon Country on Wednesday with stronger storms capable of producing frequent lightning, gusty winds, hail, and heavy rain. The threat of flash flooding will be greatest across the Four Corners states, especially in slot canyons, dry washes, and burn scars.

Forecast for Thursday:

Another active thunderstorm day is expected across the Rockies, with the exception being Northern Montana (including Glacier) who will dry out following Wednesday's activity. Storms will be capable of frequent lightning and locally heavy rain.

A little bit of moisture will sneak into the Sierra Nevada Range as well as Oregon, where a few isolated dry thunderstorms couldn't be ruled out.

Forecast for Friday:

More of the same can be expected on Friday with numerous thunderstorms throughout the Rockies, along with a continued flash flooding threat for vulnerable areas across the Four Corners region.

Outlook for Saturday to Sunday:

A stronger disturbance moving across the Northern Rockies will temporarily suppress moisture southward into the Four Corners states on Saturday, with New Mexico, Arizona, Southern Utah, and Southern/Central Colorado being most favored for thunderstorms.

However, monsoonal moisture will begin to work its way westward (into Nevada and California) and northward (into Idaho, Wyoming, SW Montana) again on Sunday with isolated thunderstorms expected.

Pacific moisture associated with a disturbance moving across the Northwest could produce some light showers over the Cascades and Olympics on Saturday, and across NW Montana/Glacier on Sunday. However, most of the rain associated with this feature will remain north of the Canadian border.

Outlook for Monday (7/18) to Tuesday (7/19):

A similar pattern will remain in place with monsoonal moisture increasing across the Central Rockies, with the extent of thunderstorm activity reaching Eastern Idaho, Southwest Montana, and Wyoming.

An active monsoonal flow will continue across the Southern Rockies as well with a daily flash flood risk for canyon country, while the Sierra and Great Basin will see a drying trend. The Pacific Northwest and far Northern Rockies should dry out during this period as well.

Outlook for Wednesday (7/20) to Wednesday (7/27):

A strong ridge of high pressure will remain in place over the Western U.S. during this period, resulting in continued above-average temperatures with the greatest anomalies over the Central and Northern Rockies. Areas along and west of the Cascades in Washington/Oregon will see temperatures closer to average.

The monsoon will remain active across the Southwest U.S. with the wettest anomalies showing up over Arizona, Southwest Colorado, and Northwest New Mexico. As a result, daily rounds of thunderstorms will likely continue across the Southern Rockies. Meanwhile, a drier pattern is expected across the Northern Rockies as well as the Northwest and West Coast. 

Thanks so much for reading! Next update on Friday (7/15).

ALAN SMITH