textproduct: Great Falls

KEY MESSAGES

- High-end and dangerous winds continue through the remainder of the day, slowly diminishing this evening and tonight.

- Colder air moving in will result in a few areas of lower elevation snow near the Hi-Line, with slick conditions developing in areas where roads are wet heading into the evening.

- After a bit of a lull on Thursday, another period of gusty winds develops across the region Thursday night into Friday. Although winds and gusts look to be lower in magnitude compared to the ongoing event, any infrastructure stressed or compromised during today will be prone to impacts at lower thresholds.

UPDATE

8 PM Update: The strongest winds have largely become confined to areas in terrain and across eastern portions of the region this evening. Some early cancellations were made to the High Wind Warnings as a result. Impactful snow has largely ended in the mountains, hence the Winter Storm Warning for the Rocky Mountain Front and Winter Weather Advisories for a few mountain ranges across Central ans Southwest Montana were also canceled early. The risk for blowing snow remains in Blaine and Fergus counties and vicinity for a couple more hours this evening, especially where falling snow continues. -AM

6 PM Update: An area of light to briefly moderate snow will continue through 8 PM or so across Fergus county and adjacent areas. Combine this with strong winds continuing through the evening and the risk for blowing snow will persist for at least a couple more hours. As such, a Winter Weather Advisory has been added to these areas through 11 PM describing forecast concerns.

Ongoing High Wind Warnings will continue for the time being, though areas near the Continental Divide have already begun to trend downward for the event. The plan for the time being is to allow for the High Wind Warnings to continue for at least a couple more hours in these areas to ensure the risk for the strong winds has diminished. -AM

DISCUSSION

/Issued 611 PM MST Wed Dec 17 2025/

- Meteorological Overview:

The remainder of today:

Sharp upper level troughing, strong low to mid-level flow, among other strong forcing mechanisms is resulting in dangerous winds across the region. Travel will be very difficult to impossible through the remainder of the afternoon and is highly discouraged unless absolutely necessary. Winds gradually decrease from west to east this evening and early overnight.

Moisture wrapping around surface low pressure in far SW SK will result in a couple hour period of falling and blowing snow in the Havre area and vicinity late this afternoon and evening. Visibility of one-half mile or less is expected at times in these areas. In addition, northwest winds moving in with this snow will result in a quick transition colder, which combined with the snow should result in slick roads. A Winter Weather Advisory was issued for this area through the evening.

Mountain snow gradually diminishes through the evening, with additional snow amounts mainly less than a few inches.

Thursday and Friday:

Brief transient shortwave ridging will result in a more benign period of weather during the day Thursday, though ample moisture will begin to move in ahead of a Pacific trough in the afternoon and early evening. Snow gradually develops in areas along the Continental Divide Thursday afternoon, persisting through Friday. A Winter Weather Advisory has been issued for areas across NW Beaverhead, where snow is forecast to begin by Thursday afternoon. Additional Winter Weather Advisories will be needed for the Rocky Mountain Front beginning Thursday evening, including Marias Pass, though for simplicities sake I have held off from issuing these until the ongoing Winter Storm Warning expires.

All the while, strong cross barrier flow will develop once again beginning Thursday evening. This will result in another windy period, though the magnitude of winds and gusts will be lesser than the ongoing event. It should be noted that infrastructure weakened by the winds today may have lower thresholds to see impacts Thursday night into Friday. Hence, even though forecast winds are lower than what is being observed today, impacts from the wind to infrastructure may be similar.

Saturday into early next week:

Persistent southwesterly flow aloft this weekend into next week will keep low-end precipitation chances in the forecast, primarily along the Continental Divide into early next week. Temperatures look to be on the warmer side of average over this timeframe, though not overly warm. -AM

- Forecast Confidence & Scenarios:

Winds today:

Strong winds will continue through the remainder of the afternoon slowly decreasing into the evening.

Surface low pressure over SW SK has resulted in another cold front dropping south from Canada late this afternoon. Winds behind this front will gradually decrease further west near Glacier county, while areas closer to the surface low in SW SK will continue to see strong wind gusts, potentially in excess of 80 kts near northern Blaine County, through the remainder of the evening.

Snow showers, colder temperatures, and slick roads this evening:

Cold temperatures and an area of snow will develop behind the Canadian cold front through the evening across the Hi-Line, with areas most favored for impacts across Hill and northern Blaine counties. Given snow is forecast to be rather brief in this area, resulting in only a couple hours or greatly reduced visibility, we opted for a Winter Weather Advisory over a Blizzard Warning. Cold temperatures moving in behind this front will result in slick roads where any wet roads quickly freeze.

Winds Friday:

Winds begin to increase again Thursday evening into the day on Friday. As mentioned above, although this wind event will be lower in magnitude compared to what is ongoing, stressed infrastructure may see greater impacts than normal. Recovery efforts may be impacted by the next period of winds Thursday night into Friday. Overall, areas with a 50% probability or greater to see a 58 mph gust include the Browning to Cut Bank areas, the Rocky Mountain Front and adjacent plains, the Great Falls to Stanford areas, Bozeman, and Ennis, among other areas in Southwest Montana. -AM

AVIATION

18/00Z TAF Period

The initial concern this TAF period will be for lingering strong winds gusts, primarily across eastern areas (Including KHVR and KLWT). A Canadian cold front has resulted in a wind shift across most of the plains, which has also resulted in areas of snow and blowing snow in the KHVR vicinity. The winds, falling snow, and blowing snow will all decrease/diminish later this evening and early overnight.

Elsewhere surface winds will continue to decrease in magnitude, though lingering stronger winds off the surface will result in LLWS concerns. Mountain wave activity will also slowly diminish through the evening and early overnight.

Looking ahead to Thursday, the main impact looks to be increasing mountain obscuration and mountain precipitation along the Continental Divide in the afternoon. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 25 46 37 48 / 20 10 30 30 CTB 8 39 28 40 / 40 0 30 10 HLN 26 40 33 47 / 20 30 70 80 BZN 23 40 32 52 / 20 30 50 80 WYS 11 30 22 37 / 20 90 100 90 DLN 23 39 32 49 / 20 40 70 70 HVR 8 35 24 40 / 30 0 30 10 LWT 17 41 30 47 / 50 10 20 40

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until midnight MST tonight for Big Belt, Bridger and Castle Mountains-Canyon Ferry Area-Eastern Toole and Liberty-Elkhorn and Boulder Mountains-Gallatin and Madison County Mountains and Centennial Mountains-Hill County-Little Belt and Highwood Mountains-Meagher County Valleys-Upper Blackfoot and MacDonald Pass-Western and Central Chouteau County.

High Wind Warning until 3 AM MST Thursday for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Judith Basin County and Judith Gap-Northern Blaine County-Snowy and Judith Mountains.

Winter Weather Advisory until 11 PM MST this evening for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft- Hill County-Northern Blaine County-Snowy and Judith Mountains.

Winter Weather Advisory from 2 PM Thursday to 9 PM MST Friday for Northwest Beaverhead County.