Forecast Highlights:

• Wet weekend (Fri-Sun) for the Northwest, Northern California, and Northern Rockies.
• Thunderstorms for the Northwest and Northern Rockies, possibly strong storms in Montana. 
• Threat for heavy rain and localized flooding for parts of the Northwest and Northern Rockies.
• Isolated thunderstorms for CO/NM Front Range foothills Friday, strong/severe storm potential early next week.
• Significant warm-up for much of the West late next week.

Synopsis:

A trough of low pressure will be spinning just off the Washington Coast from Friday through Sunday with a series of disturbances ejecting out ahead of the trough and into the Northwestern U.S. resulting in wet conditions for much of the West, while the Southwest and Southern Rockies will largely miss out on the moisture.

Significant amounts of moisture will be streaming into the Western U.S. over the weekend and the amount of water vapor in the atmosphere will be well above average across the Northwest and Northern Rockies.

 

Check out the projected 3-day precipitation totals across the West. While the Northwest and Northern Rockies will see significant rain amounts, Northern California will also receive beneficial rain this weekend.

Temperatures will be mild enough in this pattern such that snow is not expected for most mountain areas, but higher elevation ranges in the Northern Rockies such as the Wind Rivers and Beartooths could potentially see some wet snow above 10,000 feet late in the weekend. 

Forecast for Friday:

Pacific energy and moisture tracking across the Northwest will result in numerous showers and thunderstorms developing across the Cascades, Interior Northwest, and Northern Rockies, especially during the afternoon hours.

The heaviest rainfall amounts are expected across Washington, Oregon, Idaho, and British Columbia, but locally heavy rain is possible across Montana and Northern Wyoming as well.

Further south, moisture will be on the increase across the plains of Colorado and New Mexico and the moisture push could extend far enough west for isolated thunderstorms to develop along the Front Range foothills.

Temperatures will be much milder on Friday and this weekend compared to last weekend, and instability in the atmosphere will also be high with numerous thunderstorms and active cloud-to-ground lightning expected across the Northern Rockies, Interior Northwest, and even the Cascades on Friday afternoon.

We can also see the high amounts of instability projected just east of the Front Range in Colorado and New Mexico.

We could see some isolated strong thunderstorms develop across the Gallatin, Beartooth, Absaroka, and Big Horn Ranges on Friday afternoon with strong straight-line winds and large hail being the main threats along with frequent cloud-to-ground lightning.

These mentioned areas are under a Marginal Risk (level 1 out of 5) for severe weather on Friday. Further south, the threat for severe weather in Colorado and New Mexico should remain confined to the plains east of I-25.

High amounts of moisture in the atmosphere along with instability could result in locally heavy rainfall rates over a short period of time across the Interior Northwest and Northern Rockies. As a result, there is a minor risk for flooding and excessive runoff – especially in previously saturated areas and areas of complex terrain with poor drainage. 

Forecast for Saturday:

Showers and thunderstorms will become more widespread across the Northern Rockies on Saturday, especially during the afternoon and evening hours. Meanwhile, the next disturbance will reach the West Coast with moisture and rainfall extending further south into Northern California.

The heaviest rains on Saturday are expected along the West Coast and the Cascades from Washington to California just north of the Bay Area, where widespread 1-2" rain totals are likely. Tahoe could also pick up some decent rainfall, while areas further south in the Sierra look to stay dry. 

Heavy rainfall is also likely for parts of Alberta and Montana along and east of the Continental Divide, and perhaps even more so out on the plains.

Colorado, Utah, Arizona, and New Mexico should stay dry and thunderstorm-free.

Instability on Saturday will be greatest across Montana, Alberta, Idaho, and Wyoming and thunderstorms are likely across these regions as a result. Despite the heavy rain along the West Coast, thunderstorms are unlikely from Northern California to Western Washington where the atmosphere will be more stable.

A threat for localized flooding and excessive runoff will exist along the West Coast from Oregon to Northern California as well as the Northern Rockies from the Idaho Panhandle to West/Central Montana. 

Forecast for Sunday:

Another wet day is in the cards for the Northwest, Northern Rockies, and Northern California including Tahoe. Overall, the threat for heavy rainfall rates and flooding will be lower, but a good soaking rain is still likely for much of this region.

Unstable air will also extend westward into the Cascades on Sunday, resulting in a threat for thunderstorms and cloud-to-ground lightning across the Cascades of WA and OR in addition to the Northern Rockies. 

A stray thunderstorm or two couldn't be ruled out over far northern Utah and Colorado, but overall the threat looks low for these areas.

Outlook for Monday (6/6) to Tuesday (6/7):

The final disturbance in this active pattern will move across the Northwest and Northern/Central Rockies early next week with additional showers expected from Washington to Montana/Wyoming, while Colorado will also see increasing rainfall and thunderstorm chances.

Here are the projected two-day rainfall totals on Monday and Tuesday.

As energy from the northwest works its way into Central/Eastern Colorado and interacts with increasing moisture from the plains, we could potentially see some strong to severe thunderstorms develop along the eastern slopes of the Front Range in Colorado on Monday and/or Tuesday with an increasing threat further east out onto the I-25 corridor and adjacent plains. 

Outlook for Wednesday (6/8) to Wednesday (6/15):

Confidence is increasing that a strong ridge of high pressure will build over the Southwest U.S. during this period, resulting in a significant warm-up for most of the west with the first major heatwave of the summer possible from California to the Four Corners region.

Only Washington and British Columbia, as well as Northern Idaho/Montana, are projected to hang onto cooler than average temperatures at this time.

An overall drier pattern is expected across the West during this period as well. Once again the exception will be the Pacific Northwest – mainly Washington and British Columbia – where wetter conditions are likely.

It's also possible we could see periodic disturbances slipping down the eastern slopes of the Continental Divide, which could result in occasional thunderstorms along the eastern slopes of the Rockies from Montana to Colorado. 

Thanks so much for reading and have a great weekend! Next update on Monday (6/6).

ALAN SMITH

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