textproduct: Great Falls

KEY MESSAGES

- An Arctic front will move southward through the area today.

- Strong and gusty north winds will accompany and follow the Arctic front, with temperatures falling rapidly in its wake.

- Accumulating snow, heaviest in the mountains, will occur through the daylight hours today before dissipating this evening from north to south.

- This cold snap will be short-lived, with temperatures starting to warm back up on Sunday.

UPDATE

/Issued 811 AM MST Sat Dec 27 2025/

The Pacific cold front has largely exited the region this morning, just hanging on across portions of Southwest Montana. Snow has been a bit more persistent along and behind this front, especially in the Gallatin Valley. Given the favorable wind direction behind the front for lingering snow in the Gallatin Valley (West to northwest), we opted to issue a Winter Weather Advisory through 11 AM. Additional snow amounts up to two inches or so are forecast over this timeframe, particularly for areas on the southeast side of the Gallatin Valley, including Bozeman. Snow gradually diminishes late morning into early afternoon.

No changes were made elsewhere this morning. Significantly colder temperatures continue to stream in from the north behind the Canadian cold front. Temperatures across most areas will struggle to rise much, if any today. Ongoing Cold Weather Advisories and Extreme Cold Warnings are in good shape, with no changes made to those at this time. -AM

DISCUSSION

/Issued 811 AM MST Sat Dec 27 2025/

Longwave trough and attendant Pacific cold front were moving east and over the Northern Rockies early this morning, with a surface low emerging over the plains of North Central Montana and an Arctic front pushing south from Alberta. As the morning progresses the longwave trough axis and Pacific cold front will pivot east and over Southwest through North Central Montana through 18-21z all the while the aforementioned Arctic front surges south through North Central, Central, and Southwest Montana through 07-11z, 11-16z, and 16-23z respectively. A period (2-4 hours) of moderate to heavy snow will accompany the passage of the longwave trough and Pacific front; with additional light to at times moderate snow occurring along and after the Arctic front, especially in the northerly upslope regions of Central and Southwest Montana, through the late afternoon today/early evening hours tonight.

Surface high pressure rapidly building south along the Canadian Rockies will help to drive pressure rises in excess of 10mb per 6hr over much of North Central through Southwest Montana in wake of the Arctic front, which will result in a 6-12hr period of strong and gusty north winds. These northerly winds will be especially strong in lee of the Island Ranges and in terrain gaps, with the potential for surface wind gusts to approach 50kts in these locations. Temperatures will fall rapidly in wake of the Arctic front, with most of the plains of North Central and Central Montana seeing their high temperatures occur prior to sunrise today. The aforementioned strong north winds combined with temperatures plunging into the single digits above/below zero across the plains and Island Ranges of Central and North Central Montana will help to support wind chill values ranging from -25 to nearly -40 degrees through the late evening hours tonight or morning hours on Sunday. For this reason Cold Weather Advisory's and Extreme Cold Warnings remain in place. Further south across Southwest and the remainder of Central Montana (i.e. south of the Island Ranges) temperatures will be slower to cool thanks to the cold air interacting with the terrain of Central Montana, but wind chills as low as -10 to -20 degrees will still occur.

The prior mentioned surface high will continue to build south into Montana through the overnight hours tonight as the longwave trough digs towards the Upper Mississippi River Valley and ridging builds into the Pacific Northwest. This surface high and the upper level ridge building in over the Pacific Northwest will lead to clearing skies across the Northern Rockies and relaxing surface winds, which will support ideal conditions for radiational cooling through the night tonight. Low temperatures across Southwest through North Central Montana will fall to near zero to the teens below zero, with the coldest temperatures occurring near the international border and in cold prone areas that see appreciable snow over the next 12-18 hours.

The remainder of the forecast period see upper level ridging slowly building east and over the Northern Rockies, with temperatures moderating through the remainder of the weekend and early next week. - Moldan

AVIATION

27/18Z TAF Period

Post frontal snow showers (and the low potential for a heavier squall across the plains) will continue across North Central and Southwestern Montana this afternoon through early evening until high pressure moves into the area. Expect a return to widespread VFR conditions to develop after 0z with light winds and cold temperatures. Ludwig

PRELIMINARY POINT TEMPS/POPS

GTF 9 -5 24 18 / 50 10 0 0 CTB 0 -13 21 16 / 40 10 0 0 HLN 30 -1 22 11 / 60 20 0 0 BZN 29 0 21 4 / 80 20 0 0 WYS 30 -13 16 -5 / 90 30 0 0 DLN 27 2 22 6 / 50 10 0 0 HVR 9 -14 5 0 / 80 20 0 0 LWT 20 -6 20 10 / 50 10 0 0

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 2 PM MST this afternoon for Big Belt, Bridger and Castle Mountains-East Glacier Park Region- Gallatin and Madison County Mountains and Centennial Mountains- Little Belt and Highwood Mountains-Northwest Beaverhead County- Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.

Cold Weather Advisory until 5 AM MST Sunday for East Glacier Park Region-Northern High Plains.

Extreme Cold Warning until 5 AM MST Sunday for Eastern Glacier, Western Toole, and Central Pondera-Eastern Toole and Liberty.

Cold Weather Advisory until 10 PM MST this evening for Cascade County below 5000ft-Eastern Pondera and Eastern Teton-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains- Southern High Plains-Southern Rocky Mountain Front-Western and Central Chouteau County.

Extreme Cold Warning until 11 AM MST Sunday for Bears Paw Mountains and Southern Blaine-Hill County-Northern Blaine County.

Cold Weather Advisory until 11 AM MST Sunday for Fergus County below 4500ft-Snowy and Judith Mountains.