textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Quiet and Seasonable Sunday: Expect high pressure to bring dry conditions and a mix of sun and clouds today.

- Messy Monday/Tuesday Commute: Pacific moisture returns early Monday, bringing a mix of valley snow and rain with moderate snow accumulations on mountain passes.

- Midweek Winds and Snow: A cold front Tuesday night into Wednesday will bring gusty winds and more organized snow showers to the region.

High pressure will persist today over the Northern Rockies. Meanwhile, a closed low pressure circulation will spin off the Canadian coast. As the ridge over the Northern Rockies flattens on Monday, the Pacific low will send moisture onshore, reaching northwest Montana by Monday morning. Forecast models show high confidence in moisture spreading across the Northern Rockies throughout the day on Monday. Expect moderate snow for the mountain passes (Lookout, Lolo, Marias, Lost Trail), which may impact travel. The forecast is more complex for valley floors. Initial precipitation Monday morning will likely start as snow, potentially creating a slick morning commute. As warmer air moves in during the afternoon, snow will transition to a rain/snow mix or just plain rain. North-central Idaho valleys below 4000 feet should expect to see mostly rain during this period as snow levels rise.

An upper-level dip in the jet stream and an associated cold front will move through late Tuesday night into Wednesday. Expect gusty westerly winds to develop behind the front. Snow levels will drop to valley floors. There is lower confidence in the exact wind speeds for Wednesday, as model solutions vary on the strength of the cold front. However, there will be a trend toward windier and colder conditions for the middle of next week. Showers on Wednesday will become more organized, with the potential for snow banding. Snow bands can lead to rapid decreases in visibility. Showers will linger into Thursday morning, followed by a breezy afternoon. All told, the precipitation event for the coming week will bring modest totals to the valleys. However, the orographic nature of the event could result in a boost to mountain snowpack. Ensemble distributions are showing about a 20% chance for 2 inches or more of snow water equivalent for the Cabinet, Swan, Mission, and central Bitterroot ranges by Thursday morning. The news is a little better for the Clearwater and northern Bitterroot ranges, where there will be about a 30-40% chance for 2 inches.

Unsettled weather is likely to linger into next weekend as weak disturbances move through the flow. While widespread heavy precipitation is not currently expected later in the week, daily chances for light snow or rain will continue, particularly for the higher terrain.

AVIATION

High pressure, along with an easterly pressure gradient, this morning will keep VFR conditions in effect through this afternoon across the Northern Rockies airspace. Expect increasing mid and high level clouds to build this evening ahead of Pacific moisture arriving tonight. Chances for precipitation in the vicinity of KGPI will increase overnight as the weather pattern shifts to a more active period starting Monday.

MSO WATCHES/WARNINGS/ADVISORIES

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