Big Picture Weather Pattern:

A trough of low pressure will move across the Northwest and into the Northern Rockies on Wednesday. The combination of moisture, energy, and instability will favor Southern Montana for the most widespread activity on Wednesday afternoon. In the cooler sector on the backside of the trough, showers will continue across the WA Cascades and BC.

To the south, dry conditions will prevail across Arizona and New Mexico where there are several active wildfires ongoing.

View → Wildfire Hotspot and Perimeter Map

5-Day Precipitation Forecast:

Rainfall over the next 5 days will favor the Pacific Northwest and portions of the Northern Rockies. The PNW will see most of its rainfall around the end of this period as a wet system arrives on Sunday. A secondary "favored" region during the next 5 days includes the eastern ranges of Colorado and New Mexico. 

Forecast for Wed (May 29) to Thu (May 30):

Wednesday will be the more active of these two days. On the cooler backside of the system moving across the Northwest, showers will favor the Washington Cascades and much of BC with snow levels falling as low as 4,000-5,000 feet.

The Northern Rockies will be in the warmer sector during the day on Wednesday with showers and thunderstorms favoring Southern Montana, and to a lesser extent, Northern Wyoming. On Wednesday night, showers will continue across Southern Montana with snow levels falling to 6,000-7,000 feet if not lower.

Further south, isolated thunderstorms can be expected across the eastern ranges of Colorado and New Mexico, with the potential for storms to become strong or severe (large hail and/or damaging straight-line winds) as they track out onto the plains. 

Let's take a closer look at the precipitation forecast for the Northern Rockies from Wednesday morning through Thursday morning. The Madison, Gallatin, and Beartooth Ranges of Montana are in line to see the highest rainfall totals, while portions of Yellowstone National Park and the Bighorns in Northern Wyoming will see decent totals as well.

Our forecast for Gardiner, Montana (near the northern border of Yellowstone) indicates a high likelihood of showers and thunderstorms on Wednesday afternoon and evening. The image on the left shows hourly precipitation probability along with a forecasted daily rainfall total of 0.43 inches, while the image on the right shows hourly lightning chances.

Forecast for Fri (May 31) to Sat (Jun 1):

Most areas will dry out as we finish out the week, though lingering moisture will continue to result in isolated to scattered afternoon thunderstorms across the eastern ranges of Colorado and New Mexico. Only light and spotty activity is expected west of the Continental Divide in the Rockies.

The Pacific Northwest will be dry on Friday, then showers will develop across Northwest Washington and BC on Saturday as the next system approaches. 

Forecast for Sun (Jun 2) to Mon (Jun 3):

A stronger storm system will reach the Pacific Northwest with heavy rain developing across the coast of Oregon, Washington, and BC as well as the Cascade Range and the interior ranges of Idaho and BC. The Northern Rockies from Eastern BC to Wyoming can expect scattered showers and thunderstorms with locally heavy downpours as well.

A drying trend is expected further south across Colorado and New Mexico, while northernmost portions of Utah will have a slight chance of showers.

Outlook for Tue (Jun 4) to Sat (Jun 8):

A significant change to the weather pattern is expected next week as long-range models are in good agreement with a strong ridge of high pressure building over the Western U.S. This will result in a drying trend with above-average temperatures including the first serious heat of the summer for many low-elevation areas. 

Areas near and east of the Divide in the Southern Rockies from New Mexico to Colorado could see moisture intrusions from the south/southeast, and these areas will have the best chances of seeing thunderstorms during this period. 

Thanks so much for reading! Next update on Friday (May 31).

Alan Smith 

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