Mountain areas across a large portion of the Western U.S. have seen impressive rainfall over the weekend, even as far north as Washington, thanks to a substantial monsoonal moisture surge. 

Check out the radar estimate rainfall totals across the Northwest (first image) and Southwest (second image) over the past 3 days, ending Sunday morning:

On Monday, a potent disturbance is moving across the Northern/Central Rockies. Energy from this disturbance is interacting with the monsoonal moisture in place to result in widespread thunderstorms across the Rockies with the potential for heavy rain and flash flooding.

Drier air is filtering in on the backside of this disturbance, which is helping to scour out the moisture that was previously in place across Eastern Oregon and Western Idaho. 

As of early Monday afternoon, shower and thunderstorm activity was most widespread across the Northern Rockies in Montana, Idaho, and Wyoming.

Current Radar

Lightning Density

Forecast Radar

Flash Flood Watches are in effect across a large portion of the Rockies due to the potential for slow-moving thunderstorms and heavy rainfall. Elsewhere, Excessive Heat Watches are in effect for portions of the Northwest and Southwest.

As the week progresses, drier air will take hold across the Rockies in the wake of the mentioned disturbance. By late in the week, the bulk of the monsoonal moisture will become suppressed well to the south into Mexico. 

Meanwhile, a series of Pacific disturbances will impact the Northwest and Northern Rockies with wetting rains and cooler temperatures.

Early this week, temperatures will be near to below average across the Rockies, while temperatures will be above-average across the Western states, especially in the Pacific Northwest. 

However, the pattern will flip flop by later in the week with warmer temperatures shifting eastward and cooler temperatures taking hold over the Northwest by Friday.

While many areas are seeing needed rainfall, smoke continues to be an issue across a large portion of the West except for Southern California and areas experiencing southerly winds in the Intermountain West. 

The largest wildfires are present in Northern California, Oregon, Washington, British Columbia, Montana, and Central Canada. The Northwest is experiencing the worst of the smoke, but areas east of the Continental Divide are seeing lots of smoke as well.

Forecast Smoke (surface)

Forecast Smoke (sky)

Current Air Quality

Forecast for Monday, August 2nd

Widespread showers and thunderstorms can be expected throughout the Rockies from Canada to New Mexico. Heavy rain and localized flash flooding will be possible throughout this region. Drier conditions can be expected farther west, though Oregon could see some dry thunderstorms.

Forecast for Tuesday, August 3rd

Thunderstorm activity and heavy rain/flash flood potential will shift east and south on Tuesday into Colorado and New Mexico especially, while areas east of the Divide in Wyoming will see some lingering action as well. The Northwest and Northern Rockies will see more of a dry thunderstorm threat, though recent rains should reduce the fire risk.

Forecast for Wednesday, August 4th

Southern Colorado and New Mexico will see one more day of elevated thunderstorm activity and heavy rain/flash flooding potential. More isolated thunderstorms with less rainfall can be expected the farther north and west into Wyoming, Utah, Idaho, and Montana.

Forecast for Thursday, August 5th

A Pacific storm system will arrive in the Northwest on Thursday, bringing showers to the West Coast and Cascades in Washington and Oregon, and scattered showers and thunderstorms to the Northern Rockies. A weakening monsoon will shift south into Mexico starting on Thursday, leaving Colorado and New Mexico with only isolated thunderstorms and light rainfall.

Forecast for Friday, August 6th

Another Pacific system will arrive on Friday with the potential for respectable (and welcome) rains across the Cascades, while the Northern Rockies in Idaho and Montana (and to a lesser extent, NW Wyoming) will see showers and thunderstorms as well.

Some of the heavier rains with this system are expected in British Columbia, which will help the fire situation there and hopefully bring some smoke relief to areas downwind.

Farther south, thunderstorm activity will remain isolated over Colorado and New Mexico, while Southern Arizona could see a bit of an uptick as some monsoonal moisture returns from the south.

Outlook for Sat, Aug 7 - Wed, Aug 11

Additional disturbances are projected to move across the Northwest and Northern Rockies over the weekend and early next week, bringing showers and cooler temperatures. Monsoonal moisture will largely be suppressed during most of this period, except for Arizona where moisture levels and thunderstorm potential will be higher.

As we head into the middle of next week, monsoonal moisture will gradually start to increase over Colorado and Southern Utah as well with a gradual increase in thunderstorm activity expected – though still less active compared to recent weeks.

We'll see how the smoke situation shakes out with possible improvement due to rain for current fires across the Northwest, though large fires in Northern California are likely to be unimpacted.

Thanks so much for reading! Next update on Wednesday (8/4).

ALAN SMITH

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