textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Some stronger showers and storms possible this afternoon.

- Widespread showers increasing Sunday into Monday with seasonably cool temperatures persisting into early next week.

- Gradual drying trend develops mid-week alongside morning valley fog.

Shower activity will wane this morning giving way to partial afternoon clearing. Solar heating will generate weak to modest instability, supporting spotty afternoon showers and thunderstorms capable of brief heavy rainfall, lightning, hail, and erratic convective outflow gusts of 25 to 45 mph. Persistent moderate showers will continue tonight across western Montana.

An upper-level closed low will track directly across the Northern Rockies Sunday through Monday before departing Saskatchewan-bound by Tuesday. Dynamic forcing and rich moisture advection will produce widespread, soaking rainfall. Probabilities for rainfall exceeding 0.50 inches are very high between Sunday morning and Tuesday morning reaching 80 to 90+ percent across West- Central and Northwest Montana, 60 to 80+ percent across North-Central Idaho, and as low as 60 percent for Southwest Montana. A 50 percent chance exists for total rainfall exceeding 2.00 inches from the Flathead Lake region extending north and east across the Glacier Region. Cold air entrainment aloft will lower snow levels, producing some mountain snow accumulations above 9,000 feet.

The forecast becomes a bit uncertain toward the middle part of next week, but what we know so far is: The closed low exits to the northeast on Tuesday, allowing high pressure to build over the region into the middle of next week. This pattern will bring a drying trend with moderating temperatures, though lingering boundary-layer moisture will continue to support overnight and early morning valley fog and low stratus.

AVIATION

Morning showers will decrease in coverage and give way to partly cloudy skies across the region. Scattered showers and thunderstorms are possible across western Montana and could impact KMSO and KHRF. Expect generally weak winds at the terminals. Persistent light to moderate rain showers are expected overnight through Sunday morning impacting KGPI, KMSO and KHRF. More scattered showers and thunderstorms are possible on Sunday.

MSO WATCHES/WARNINGS/ADVISORIES

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