textproduct: Great Falls

KEY MESSAGES

- Wintry weather moves into the area overnight tonight and tomorrow morning, bringing widespread snow and localized freezing rain to the Hi-Line.

- Drier for midweek, but still a few snow showers around with temperatures near to below normal.

- Another round of snowy weather looks likely next weekend, with the coldest air of the season likely pushing in behind the snowfall.

UPDATE

Updated forecast is out for this evening. Main adjustment was just to the timing of the current winter statement. The latest NAM has the precipitation beginning closer to 6 AM in the Havre/Harlem areas, along with the precipitation going into Monday evening in this area. Thus just some adjustments to the start/end time for this area. Otherwise, the overall forecast is on track.

Overall, there hasn't been much precipitation on radar over the entire Pacific Northwest until the past hour. The storm is just starting to develop, with precip developing quickly now over eastern Washington/eastern Oregon. This area of precipitation will move east of the divide after Midnight and then into the Havre/Harlem areas on Monday morning.

Colder air is already moving south of the border, with temperatures in the 20s around Shelby. With warmer air aloft, some of the precip will fall in the form of rain and freeze on contact after Midnight in the Cut Bank/Shelby/Sweet Grass area. This includes portions of I-15 in this area. Colder air will move in during the day on Monday, changing the rain to snow.

For areas further south, in the Great Falls/ Helena/ Bozeman areas, the precipitation is also likely to start out as rain, but then change to snow as well. However, since temperatures are still in the 40s, combined with a warm ground, the chance for freezing precipitation is lower in these areas at this time.

Overall, this is the first of several weather disturbances this week, with each disturbance bringing in colder and colder air. By next weekend, the GFS model has air temperatures ranging from 10 below to 20 below across portions of North Central MT. At this time, the GFS is one of the colder models, but this probability is possible should we develop a good snow cover this week and get some clearing skies overnight next weekend. Brusda

DISCUSSION

/Issued 451 PM MST Sun Nov 23 2025/

- Meteorological Overview:

Upper level ridging currently over the area today will break down overnight tonight and tomorrow as a shortwave approaching the Northwestern US begins to influence the area. For tonight, that will generally mean increasing cloudiness, though for the Continental Divide and the Hi-Line, the impacts will begin to be felt overnight as snow begins in the higher terrain and some rain or even freezing rain begins to fall along the Hi-Line overnight tonight. Precipitation will begin to spread southward and eastward quickly tomorrow morning as colder air surges into the area, with a period of rain for lower elevations quickly changing over to snowfall as temperatures fall. For most lower elevations, snowfall will struggle to accumulate on roads and sidewalks, but in the higher terrain colder temperatures overnight tonight and higher snowfall rates will allow for some accumulations, with some of the highest passes like Kings Hill Pass on track to see at least 6 inches of snowfall through tomorrow afternoon and evening.

High pressure will build into the area on Tuesday behind this system, bringing a bout of cooler, but closer to normal temperatures for the midweek, though northerly winds may allow for some scattered snow showers, especially along the Rocky Mountain Front and on the north slopes of the Little Belt and Snowy Mountains (Great Falls to Lewistown Corridor). More widespread light snowfall is possible on Thanksgiving Day as an elevated warm front lifts through, though accumulations on Thursday should be light.

Snowfall may increase in intensity overnight Thursday as another surge of cold air starts to push into the area, clashing with the warm air aloft trying to work into the area. While uncertainty remains with the snowfall with this system, one thing that continues to be clear is that there is an increasing likelihood of the first arctic air mass of the season pushing into the area over the weekend, with widespread subzero temperatures continuing to be a substantial possibility (>40% for most areas by early next week). -Ludwig

- Forecast Confidence & Scenarios:

Accumulating Snow and isolated freezing rain tonight through Monday evening...

Winter Weather Advisories remain in effect for the Southern Rocky Mountain Front, Big Belt, Bridger and Castle Mountains, Little Belt and Highwood Mountains, Bears Paw Mountains and Southern Blaine County where probabilities for 4" or more of snow range from a 50- 75%. While initially warm ground temperatures will lead to some melting across these locations snowfall rates of 1/2" per hour or more during the daylight hours, which have a 30-60% chance of occurring, will lead to snow accumulating even on warm surfaces.

The Winter Weather Advisory for the East Glacier Park Region remains in effect; however, there is growing concern that the combination of heavy snow and strong winds could significantly reduce visibilities west of East Glacier and over Marias Pass. Additionally, probabilities for 8" or more of snow over Marias Pass are now at a 65% chance, with even a 25% chance of 12" or more of snow. Future shifts may need to consider upgrading the advisory to a warning, but for now we will hold onto the advisory to see if the trend for higher snowfall amounts holds.

In addition to the snowfall, confidence is increasing in at least some isolated to scattered freezing rain along the Montana Hi Line east of Cut Bank, including I-15 near the Canadian border. Road temperatures remain around 50 degrees as of 3PM today, but are likely to get very close to, if not just below, freezing overnight as some rain manages to fall. While most areas should see roads stay just above freezing, any bridges and overpasses seem likely to see some ice accretion overnight tonight and early tomorrow morning, which has prompted the issuance of an additional Winter Weather Advisory for these areas. - Moldan/Ludwig

Late Week System

Models continue to suggest that late next week could be on the snowy and cold side as a big pattern change continues to come into increase in likelihood. Current NBM probabilities have continued to slowly adjust upward for a few inches of snow late next week for just about the entire state, with most of the area along and north of a Helena to White Sulphur Springs line having a 50% chance for at least 2-4 inches of snow Friday through Saturday. Behind this snow, temperatures look to plunge into the deep freeze, with around a 40% or higher chance of subzero temperatures area wide by early next week. With much uncertainty remaining on what could be an impactful period, be sure to monitor later forecasts as details become clearer. Ludwig

AVIATION

24/00Z TAF Period

Generally quiet conditions will prevail over the CWA this evening. Then expect increasing chances for rain/snow to develop after 07z Mon, with scattered areas of precip continuing through Monday afternoon. Colder air will move into the CWA during the morning hours, thus the rain will change to snow. Some freezing rain is possible along the Highway 2 corridor between Browning and Harlem. Mountains/passes will be obscured at times across the CWA throughout the day on Monday. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 39 47 21 38 / 30 80 60 0 CTB 31 39 13 33 / 30 80 30 0 HLN 34 42 19 36 / 30 70 40 0 BZN 32 45 14 35 / 20 80 20 0 WYS 24 35 6 28 / 10 90 30 0 DLN 32 45 12 35 / 10 40 0 0 HVR 29 43 16 35 / 10 90 70 0 LWT 34 47 16 34 / 20 70 50 0

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 11 PM this evening to 11 PM MST Monday for Big Belt, Bridger and Castle Mountains-East Glacier Park Region-Little Belt and Highwood Mountains-Southern Rocky Mountain Front.

Winter Weather Advisory from 6 AM to 11 PM MST Monday for Bears Paw Mountains and Southern Blaine-Hill County-Northern Blaine County.

Winter Weather Advisory from midnight tonight to noon MST Monday for Eastern Glacier, Western Toole, and Central Pondera-Eastern Toole and Liberty.