textproduct: Great Falls

KEY MESSAGES

- Periods of mountain snow and scattered lower elevation light rain, snow, or mixed precipitation continue for much of the week.

- Near to above average temperatures are generally expected, but Arctic air will periodically move into central and north-central Montana.

UPDATE

Current forecast remains on track during the daytime hours today. The wave of snow will continue to move north into Southwest MT this morning. Snow levels will slowly rise throughout the day, which will keep snow at or above pass level later this afternoon. -Wilson

DISCUSSION

/Issued 447 AM MST Sun Dec 21 2025/

- Meteorological Overview:

An approaching shortwave trough will send a warm front and Pacific moisture into the Northern Rockies today. Mountain snow and some lower elevation rain/snow will move northeastward as the day progresses, mostly impacting central and southwestern MT in addition to areas along the Rocky Mountain Front. The precipitation looks to peak tonight into Monday morning before diminishing later in the day as the trough axis moves off to the east. The primary concerns will be accumulating snow over the mountains, but warming temperatures aloft may encourage some spotty light freezing rain or drizzle develop over some central/southwest valleys this evening and tonight and then over the Milk River Valley tonight into Monday morning.

Following the trough passage, the Arctic boundary will begin to slide southward Monday evening/night, but shouldn't get much farther south than the Hi-Line before slowly retreating northward again on Tuesday. An increasingly mild and moist southwesterly flow becomes established over the Northern Rockies Tuesday night into Wednesday in response to a deepening closed low along the Pacific NW coast. This will bring initial round of mountain snow and some lower elevation precipitation Tuesday night into Wednesday. Once again, some light freezing rain or drizzle may develop along the Milk River Valley where shallow cold air may be slower to exit.

Then a stronger shortwave ejects eastward from the closed Pacific low Wednesday night into Thursday. This system looks to bring a more widespread area of snow while an Arctic front moves into central/North-central MT. The Arctic air retreats northward again on Friday in advance of another approaching shortwave. This next system will bring more mostly mountain snow and another southward advance of Arctic air behind it, though it's uncertain how far south the colder air will get. - RCG

- Forecast Confidence & Scenarios:

Snow and spotty light freezing rain/drizzle through Monday morning...

The precipitation today through Monday morning will generally be on the lighter side with most mountain areas seeing snowfall amounts ranging from trace amounts up to a couple inches. The exceptions will be in the Chief Joseph Pass area and over the Madison/Gallatin mountain ranges where there is a 70 to 80% chance for snowfall amounts at or greater than 3 inches through Monday morning. Additionally, there are concerns for some light freezing rain or drizzle over some central and southwest valleys, including the Wisdom area. This is based solely on forecast soundings and the anticipation of cold ground surfaces and isn't supported by NBM probabilities. Given these concerns, a winter weather advisory was issued for the aforementioned areas.

There are also some concerns for some freezing rain/drizzle over some of the central valleys, including Helena, Lincoln, and the White Sulphur Springs area this evening and tonight. No winter weather advisories have been issued for these areas due to lower confidence of colder ground surfaces and no support from NBM probabilities. Similarly, there is a concern for spotty light freezing rain/drizzle over Milk River Valley. Here there is higher confidence for cold surface temperatures but less than a 20 to 30% chance for measurable precipitation. All of these areas will continue to be monitored. - RCG

AVIATION

21/12Z TAF Period

Clouds and areas of snow, rain, or mixed precipitation will increase from south to north in advance of an approaching shortwave trough. Central and southwestern areas will be most susceptible to low VFR or MVFR conditions through 21/18Z before moving into central and north- central MT later this afternoon into tonight. There is a slight chance for some spotty light freezing rain or drizzle in the KHLN/KHVR/KLWT areas tonight, but there is less than a 20% chance for measurable ice accumulation for all three locations. Mountain obscuration will increase today and continue for the remainder of the TAF period. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 41 31 45 24 / 20 30 20 0 CTB 36 21 37 15 / 0 30 0 0 HLN 37 30 43 26 / 40 50 50 10 BZN 41 33 47 30 / 70 60 70 20 WYS 39 33 40 30 / 100 90 100 80 DLN 41 33 46 30 / 70 60 40 20 HVR 37 21 35 13 / 0 30 30 0 LWT 41 30 44 26 / 40 40 40 10

TFX WATCHES/WARNINGS/ADVISORIES

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