Monday (June 1):

The low pressure system that was responsible for significant rain across the Northern Rockies last weekend will linger over Northern Montana on Monday.

Northeast winds on the backside of the low will continue to reinforce deep moisture across the eastern slopes of the Rockies in Northern Montana and Alberta, with additional heavy rain expected. Areas west of the Divide, including the Northern Idaho Panhandle and Southeast BC, will see some more showers as well.

Snow levels are starting out around 6,000 feet in Glacier National Park, with snow falling at Logan Pass (elevation 6,600 feet). As the day progresses, snow levels will rise above 7,000 feet with snow changing back to rain at Logan Pass.

Snow Level Forecast Range Chart for Logan Pass:

Further south in Colorado and Southeast Wyoming, low-level moisture from the Gulf of Mexico will sneak into the area via southeast winds, resulting in scattered afternoon thunderstorms east of the Divide.

Storms will initially develop over the Front Range foothills shortly after noon, with the highest threat of lightning expected across the Denver Metro area between about 2:00 and 5:00 pm on Monday afternoon. Cheyenne and Southeast Wyoming can also expect scattered thunderstorms around this time. 

StormNet Lightning Risk for 3-4pm on Monday:

Large hail (1+ inch diameter) also cannot be ruled out with stronger storms along the I-25 corridor, though the risk will be higher further east out on the plains.

Tuesday (June 2):

The low pressure system will gradually lift to the northeast into Canada, but lingering moisture via NNE flow will contribute to additional light showers along the eastern side of Glacier National Park as well as the Canadian Rockies. 

Additional two-day rain totals on Monday-Tuesday (including liquid-equivalent precipitation in areas that receive snow) will range from 1-2 inches along the eastern slopes of the Continental Divide from Glacier National Park to Waterton Lakes to just south of Canmore, Alberta, with lighter totals on the west side of the Divide.

Here is our PEAKS Model Precipitation Forecast:

To the south, low level moisture from the east will increase across New Mexico on Tuesday afternoon and Tuesday night, resulting in numerous showers and thunderstorms with beneficial rains expected.

The Front Range foohills in Colorado could also see localized downpours with any afternoon showers and thunderstorms that develop.

Lightning potential on Tuesday afternoon will be highest across the southern half of New Mexico, mainly along and south of I-40. Thunderstorm activity looks more isolated along the Colorado Front Range and Sangre de Cristo Range in CO/NM. 

Wednesday (June 3):

A trough will move into the Pacific Northwest and a cold front will also push from west to east across BC, Washington, and Oregon, leading to a noticeable cooldown.

Moisture levels will not be overly impressive with mainly light showres developing along and west of the Cascades in Washington, while showers will be fewer and lighter in Oregon.

Ahead of the cold front where the airmass will be less stable, locally heavier showers and isolated thunderstorms will develop across the Inland Northwest and Northern Rockies.

To the south, low level moisture will remain in place across New Mexico with showers and thunderstorms expected. 

Lightning activity is expected to be more widespread across New Mexico, including higher probabilities in the northern mountains around Taos and Santa Fe. 

In Colorado, thunderstorm activity will be more isolated overall and rainfall will be lighter and more spotty. However, areas west of the Divide will see a comparatively higher chance of thunderstorms than recent days.

Also, StormNet is noting a locally higher lightning risk around Pikes Peak and Colorado Springs, as well as the eastern plains.

Thursday (June 4):

A shortwave trough will track across the Northern Rockies along with a weakening cold front. This will favor additional showers across Central and Northern Montana as well as the Canadian Rockies, though only isolated lightning activity is expected due to a relatively stable atmosphere. 

To the west, a stronger trough will reach the coast of British Columbia with rain developing over Vancouver Island and the Coast Range, including snow down to 5,000 feet or lower around Whistler. Light showers will also extend as far south as the Northern Olympics and Northern Cascades in Washington on Thursday.

Moisture will be on the decrease across New Mexico and Colorado, but there will still be enough lingering moisture and instability for isolated to scattered thunderstorms.

The best chance of mountain thunderstorms will be in the Sangre de Cristo Range in Northern New Mexico and Southern Colorado, with lower probabilities further north in Colorado. 

Friday (June 5) to Sunday (June 7):

A trough is projected to move across the PNW and into the Northern Rockies over the weekend, bringing cooler and wetter conditions. To the south, lingering moisture will result in afternoon thunderstorm chances across parts of Colorado and New Mexico, with generally light rain expected. 

The map below shows projected 3-day rain totals from the European AIFS Ensemble Model, which represents the average of 50 simulations. The heaviest rain totals are projected along and west of the Cascade Crest in Washington and Northern Oregon, as well as the BC Coast Range.

A secondary area of heavier precipitation is projected across the interior mountains of British Columbia.

June 8-12:

Next week, a weak troughing signal is projected near the West Coast with a ridging signal near and east of the Continental Divide. This will likely result in a warm-up to above-average temperatures across the Central Rockies and adjacent plains, with more seasonal temperatures across the Pacific states.

Longer-range models are favoring continued shower chances across the Pacific Northwest and Northern Rockies.

There is also a weak signal for continued thunderstorm chances across parts of New Mexico and Colorado, but it looks like more of an isolated storm setup with light rainfall, as opposed to a more active monsoon pattern we would expect later in the summer.

Thanks so much for reading! Next update on Wednesday.

Alan Smith