textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Slippery Travel: Occasional freezing rain and snow will result in slick travel conditions this morning, tonight, and again on Saturday morning for valleys and mountain passes.

- Weekend Warmth: Temperatures will trend upward through the weekend and peak on Sunday, with widespread highs in the 40s and 50s likely.

- Monday System: A weak disturbance returns Monday bringing valley rain and mountain snow, followed by warming temperature trends for the remainder of the week.

Northwesterly flow aloft this morning will transition to westerly with the passing of a weak shortwave trough this afternoon. There will be enough Pacific moisture to bring some showers to the Northern Rockies today, though forcing for ascent remains weak and temperatures remain warm. The resulting precipitation type and distribution will be light rain in the valleys with snow in the higher peaks. Snow levels start out at about 4000 ft this morning, rising to about 5000-6000 ft this evening. Northwest Montana will be favored for snow as the Cabinet, Whitefish, Swan, and Mission ranges, as well as Glacier Park, will see an inch or two to about half a foot by tonight. Expect diminishing returns south of about Interstate 90. Despite rising snow levels, valley cold pools may persist, which would result in light freezing rain. Isolated to widely scattered slick travel conditions will be possible this morning and again late tonight into early Saturday morning.

A ridge of high pressure along the west coast will continue to progress eastward and strengthen over the Northern Rockies through the weekend. Daytime high temperatures will begin to creep well into the 40s and 50s by Saturday and Sunday for many valley locations, approaching daytime record highs. The peak of this short-term warming trend looks to be on Sunday, when confidence is highest. During this timeframe, the lower Salmon River Valley will have the highest probability of nearing the 60-degree mark.

A brief breakdown of the ridge arrives on Monday as a shortwave trough moves through the Northern Rockies. Snow levels will remain high, generally above 4,000 feet, so valley precipitation will likely fall as rain. Be aware of possible slick spots overnight or early morning, while mountains and passes see minor snow accumulations.

While earlier forecasts spoke of a strong ridge rebuilding for the middle to end of next week, confidence in the hottest temperature scenarios has decreased slightly. Though warmth and even record warmth is still in the forecast, much of the Northern Rockies will remain under west-northwesterly flow aloft, with North Central Idaho seeing the best chances for a southwesterly wind gradient, better mixing, and the warmest temperatures throughout the region.

AVIATION

Continuing light precipitation will bring brief reductions in visibility across the Northern Rockies airspace. Expect periods of low visibility down to about 2-3SM at KMSO and KGPI into this evening, along with obscured terrain throughout northwest Montana. While valley precipitation will be in the form of rain, there remains a slight chance (5-10%) for freezing rain this morning, and again on Saturday morning. Ceilings at KGPI this morning will be around 3,000 ft. West or southwesterly winds over mountain crests increase this afternoon to about 30-40 knots, primarily for northwest Montana.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.