textproduct: Great Falls

KEY MESSAGES

- A period of mixed precipitation, including freezing rain and drizzle, along with patchy fog develop over the plains by this evening and continues through Christmas morning while light snow falls over the higher terrain.

- Strong, gusty southerly winds develop over the southwest tonight through Wednesday night, strongest in the Madison River Valley.

- Another weather system and attendant cold front will bring a period of areawide light snow late Friday into Saturday while Arctic air moves onto the plains.

- Near to above average temperatures are expected for most locations later this weekend into early next week, but Arctic air may linger in the normally colder north-central river valleys.

UPDATE

/Issued 913 AM MST Wed Dec 24 2025/ Updated forecast is out. Main adjustment was for today, just adjust towards current trends for temps/winds. Otherwise, most precipitation will hold off until late afternoon.

The high wind warning will continue for the Norris Hill area. Winds should increase this afternoon and then diminish mid evening.

The main concern for tonight and into Christmas morning will be the potential for freezing rain over North Central MT. Overall, the 12z runs are decreasing the amounts/coverage area. We will look at this closer, but current thinking is that only a winter weather advisory will be needed for freezing rain for some areas overnight and into Christmas morning. Brusda

DISCUSSION

/Issued 913 AM MST Wed Dec 24 2025/

- Meteorological Overview:

A mild south/southwesterly flow aloft will continue to become established over the Northern Rockies through tonight. Low stratus, patchy fog, and spotty light wintry mixed precipitation develops along the Hi-Line later today and slowly expands southward into central and north-central MT by this evening.

Then a shortwave trough moves northeastward into the Northern Rockies and brings a period of widespread precipitation this evening through early Christmas morning. H700 temperatures warm to around 0C this afternoon and evening and only fall to around -5C behind an elevated cold front later tonight. These temperatures will be well capable of producing mixed wintry precipitation, including freezing rain, over the shallow colder air mass residing in central and north- central MT. The weak frontogenesis with this system will also elevate precipitation amounts up to around a tenth of an inch with a narrow area seeing localized amounts up to around a quarter inch. At least light to moderate impacts from ice glazing seem plausible over the golden triangle area northeastward into the Milk River Valley.

This system will bring mostly light snow over the mountains with most central/southwest valleys seeing plain rain. With that being said, some of the normally colder valleys will have a 10 to 15% chance for light freezing rain or drizzle given temperatures near freezing. Strong winds with this system look to be limited to the normally wind prone southwest valleys and mountain peaks where 40 to 50 kt southerly H700 winds will transfer to the surface through this evening.

Precipitation diminishes and temperatures rebound rather quickly Christmas day as warmer air moves northward ahead of the next approaching shortwave trough. The one exception to this will be over the Milk River Valley where below freezing temperatures may stick around for much for the day. The aforementioned shortwave looks to merge with a colder system and is progged to move into the Northern Rockies and bring a round of light snow for most locations and a southward intrusion of Arctic air later Friday into Saturday. Northwesterly flow aloft will set up heading into early next week while high pressure builds to our west. Milder air does look to return for most locations, but the colder air may be reluctant to leave the normally colder river valleys of north- central MT. Additionally, passing shortwaves may bring brief cool downs and even lower end rain/snow shower activity. - RCG

- Forecast Confidence & Scenarios:

A period of wintry mixed precipitation, including freezing rain and drizzle over the plains this evening though Christmas morning...

The heaviest precipitation looks to set up within 50 miles of a Great Falls to Havre line where there is a 30 to 50% chance for ice accumulations over a tenth of an inch. Temperatures will definitely have an impact on how this event ultimately unfolds. Colder air on the northern fringe may be just deep enough for the precipitation to mix with more snow or even sleet, reducing the window of opportunity for freezing rain accumulation. On the other hand, areas close to the central island ranges may warm up above freezing before dawn and reduce the overall impacts there. This system will move quickly through the forecast area, so that will also reduce the residence time of the precipitation. Never the less, a winter storm watch was posted for much of north-central MT to cover potential impacts, including icy roads/sidewalks making travel/walking outdoors dangerous and ice accumulation on power infrastructure causing outages. Icing may also impact the aviation community with exposed metal surfaces being covered in ice. - RCG

AVIATION

24/18Z TAF Period

The initial concern this TAF period will be for persistent low clouds across portions of the plains. An area of mountain snow, lower elevation rain in Southwest Montana, and a mix of lower elevation rain and freezing rain across the plains develops from southwest to northeast this evening into tonight, ending Thursday morning. Mountain obscuration will be common this TAF period, especially around areas of precipitation. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 26 20 45 34 / 0 80 70 10 CTB 20 11 38 26 / 10 50 40 0 HLN 41 34 49 32 / 0 70 40 20 BZN 46 36 49 32 / 0 50 60 20 WYS 42 32 39 27 / 70 90 90 80 DLN 46 37 45 32 / 10 70 40 30 HVR 29 19 31 24 / 0 90 60 10 LWT 53 29 46 34 / 0 50 60 10

TFX WATCHES/WARNINGS/ADVISORIES

Winter Storm Watch from 6 PM MST this evening through Thursday morning for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Hill County-Northern Blaine County-Southern High Plains-Western and Central Chouteau County.

High Wind Warning until 8 PM MST this evening for Madison River Valley.