textproduct: Great Falls

KEY MESSAGES

- Periods of mountain snow with lower elevation rain/snow through the week.

- There's a slight chance for freezing rain along the Hi-line tonight and tomorrow morning, with low chances returning late Tuesday into Wednesday morning.

- Temperatures remain warmer across Southwest Montana this week, with arctic air intruding into North-Central MT at times.

UPDATE

/Issued 906 PM MST Sun Dec 21 2025/

No major changes to the forecast. Still watching for some freezing rain/drizzle in the valleys of Southwestern Montana and along the Hi Line late tonight and early tomorrow morning.

DISCUSSION

/Issued 906 PM MST Sun Dec 21 2025/

- Meteorological Overview:

An upper-level shortwave moving through the region today and Monday along with a 700mb front lifting north will continue to bring mountain snow and lower elevation rain/snow this afternoon. This southwest flow pattern bringing warm air advection will increase snow levels throughout the day. The arctic air mass intruding into the Hi- line tonight will keep colder air at the surface. Overrunning warm air will pose a threat for light freezing rain tonight, mainly along the Hi-line. There is also a low end chance for light freezing/freezing drizzle in Southwest MT tonight.

A more broader trough building along the Pacific Coast this week will keep periods of mountain snow and lower elevation rain/snow. Tuesday through Wednesday morning, another warm front lifts north, bringing more warm air advection. This will collide with the arctic airmass intruding into the Hi-line again, which will bring another low chance for freezing rain.

A more widespread system moves in late Wednesday through Christmas, with the arctic front attempting to push farther south into North- Central MT. This will be the better day this week for light snow to fall at lower elevations along the plains.

- Forecast Confidence & Scenarios:

The current system looks to remain on track for light snow along the Southwest MT mountain passes and more moderate snow at the higher peaks through Monday morning. Snow levels are likely to rise to 7,000ft later this evening across the Southwest MT mountains. With the incoming warm air advection, I can't rule out some mixed precipitation/light freezing rain to mix in with snow at the passes/lower elevations across NW Beaverhead County and the Gallatin and Madison County Mountains. There remains a little uncertainty if freezing rain develops in other Southwest valleys/mountain passes later tonight through Monday morning. One area to watch is the Dillon and Helena Valley. Temperatures are rising above freezing there this afternoon, which lead me to hold off on any Winter Weather Advisories over there. However, if they do start to cool back to below freezing then light freezing rain development is not out of the picture. For the Boulder Hill/Lincoln area, soundings look to keep the warm nose just below freezing, and keeps it mainly light snow. However, if they get a more robust warm nose, then they too can get light freezing rain.

Best confidence for freezing rain development tonight and Monday morning is along the Hi-line, though chances still look marginal at best. Models are still wishy-washy on if the Hi-line gets any precipitation over night, but with the arctic air intruding in later tonight, I am confident in that any precipitation that develops will be light freezing rain. Therefore, I issued a Winter Weather Advisory for the Hi-line plus Chouteau County tonight through Monday morning, for a marginal confidence, but more impactful event. There is a slight chance for a westward expansion if there is higher confidence the Rocky Mountain Front developing appreciable overnight precipitation.

Another warm front lifting north tomorrow, with bring another marginal chance for light freezing rain across North-Central MT Monday night through Tuesday morning, but there is lower confidence for appreciable precipitation making it that far north. -Wilson

AVIATION

22/06Z TAF Period

North-Central Montana (KCTB, KHVR): VFR conditions will persist across the Hi-Line through the period except around isolated showers early on in the period around KHVR. There is a potential for some light FZRA at KHVR through the early morning hours, however, the greater threat is expected to stay to the east. Accumulations up to a light glaze are possible wherever FZRA occurs. Otherwise, as the clouds start to break in the late morning, expect increasing winds at KCTB through the afternoon hours.

Central Montana (KGTF, KHLN, KLWT): For the most part showers will stay along the mountains surrounding KHLN but there is a concern for some light FZRA during the early morning hours. Accumulations up to a light glaze are possible where FZRA occurs. Otherwise a wintry mix is possible through 21/18Z before precipitation starts to exit the area. For KLWT, showers are possible through the first 12 hours of the period and are at a much lower confidence of impacts compared to locations south and west. After 22/18Z, clouds start to gradually lift giving way to some breezy conditions at KGTF. Mountain obscuration will remain a concern through 22/18Z before the cloud deck starts to lift across central Montana.

Southwest Montana (KBZN, KEKS): Rain/snow mix will transition to rain as the warm front moves through over the next few hours. MVFR/IFR conditions are expected to linger across southwest Montana through around 22/18Z before precipitation moves out of the area. There is a concern through 22/20Z that periods of LIFR may develop around KBZN due to lingering fog. Right now, confidence is not high enough to put it in the TAF but 1SM or less visibility cannot be ruled out at some point during the early morning hours. Once the precipitation and any lingering fog moves out of the area, VFR conditions will persist through the rest of the period. Mountain obscuration will be at its highest through 22/20Z but obscuration of the mountain peaks is possible through the entire period. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 33 46 26 46 / 20 20 0 0 CTB 21 39 15 39 / 10 10 0 0 HLN 29 43 28 44 / 70 60 10 20 BZN 30 46 30 48 / 70 80 20 20 WYS 33 40 31 43 / 100 100 90 40 DLN 32 46 31 47 / 70 60 20 10 HVR 21 37 12 31 / 20 20 0 0 LWT 31 45 27 49 / 50 50 20 10

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 11 AM MST Monday for Eastern Toole and Liberty-Hill County-Northern Blaine County-Western and Central Chouteau County.

Winter Weather Advisory until 9 AM MST Monday for Gallatin and Madison County Mountains and Centennial Mountains-Northwest Beaverhead County.