textproduct: Great Falls

KEY MESSAGES

- Periods of light mountain snow will continue through Wednesday.

- A fast moving weather system will bring breezy conditions and periods of mountain snow this weekend.

- Cooler and wetter weather is expected next week leading up to Thanksgiving.

UPDATE

/Issued 821 PM MST Tue Nov 18 2025/

Tonight into tomorrow morning there will be light mountain snow. In areas that clear across the valleys of Southwestern Montana and across the Hi-Line fog will form tonight into early tomorrow morning. However there is low-confidence in areas clearing enough for dense fog to form. Current satellite imagery shows a few areas of fog in Hill and Blaine counties but based on camera observations it is not dense at this time. The forecast is on track with no update planned. -IG

DISCUSSION

/Issued 821 PM MST Tue Nov 18 2025/

- Meteorological Overview:

A moist, but weak, southwesterly flow aloft persists until Wednesday when a Pacific trough passes through the Northern Rockies. This will maintain variably cloudy skies and spotty areas of light precipitation. Snow levels will be lowest on Wednesday while the trough axis moves overhead; however, negligible precipitation amounts and the lack of colder air aloft will offer little support for accumulating snow. Overnight and morning low stratus and patchy fog will continue to be a concern through Wednesday morning, especially near the Hi-Line; however, abundant mid- and high level clouds should limit the overall coverage and impact from dense fog.

Weak ridging aloft will bring dry and mild conditions for the second half of the work week while the northern jet stream stays in Canada and a closed low slides down the California coast. The upper level jet moves southward into the Northern Rockies this weekend and brings periods breezy to windy conditions, cooler temperatures, and some mountain snow. A northwesterly flow aloft develops and sends a series of colder troughs through the state heading into the Thanksgiving holiday. This looks to bring periods of mostly light snow and the coldest temperatures of the season so far. -RCG

- Forecast Confidence & Scenarios:

Fog Tonight:

There is around a 20% chance for fog development along the Hi-Line and valleys of southwestern Montana overnight. The limiting factor in confidence is the timing of the low stratus deck expected to push through. If skies are unable to clear out and the stratus deck moves in first then fog will not be an issue. Otherwise, there could be some patchy dense fog in locations that clear out tonight.

Mountain Snow and Lower Elevation Rain Tonight/Wednesday:

Light mountain snow is expected to linger around through Wednesday afternoon. Snow amounts from here on out are not expected to amount to much at pass level and below with only the peaks potentially seeing up to a couple additional inches of snow. For lower elevation rain, accumulation is generally expected to be minimal with southwest Montana having the highest chance for seeing light rain.

Wind and Snow This Weekend:

Snow amounts along the Northern Rockies have decreased from the previous model runs which is not to say that locally higher amounts are not possible but rather confidence is decreasing in these occurring. The latest model guidance has a 10-30% chance of the Northern Rockies exceeding 2 inches and a 10% chance of exceeding 4 inches at the peaks. As of now there low confidence in significant impacts to Marias Pass with the most likely scenario being less than an inch at pass level and below.

When it comes to wind gusts in excess of 55 mph, there is a greater than 80% probability along the Rocky Mountain Front dropping off to a 50% chance around Cut Bank. The probabilities on Saturday are slightly lower with a 60-80% chance along the immediate Rocky Mountain Front decreasing to 50% chance around Cut Bank. Overall the two days are expected to be fairly windy but there are currently no indications or confidence in reaching high wind criteria at this time.

Wind, Cold, and Snow Thanksgiving Week:

There are still high levels of uncertainty regarding the week of Thanksgiving. The highest confidence lies in that there will be a trough that moves over the western CONUS next week. Everything else from the snow amounts to the cold temperatures keeps changing enough with each model update that it is difficult to pin down any specifics at this time. The latest run of the models ran a little drier and colder than the previous runs. Notably the GFS wants to run a little colder than the Euro which could impact not only how much snow the lower elevations receive but how cold it gets in the wake of the front.

One of the additional items to watch will be the wind, particularly at the start of the event on Monday/Tuesday. The GFS continues to increase upper level winds Monday afternoon into Tuesday morning across north-central Montana. Right now the NBM is erring on the side of caution and maintaining lighter winds in the forecast but this will be something to watch in the coming days as it is possible there could be impactful wind ahead of the cold temperatures moving in. -thor

AVIATION

19/06Z TAF Period

VFR conditions will prevail across the KEKS, KHLN, and KCTB terminal. At KLWT, KGTF, and KBZN terminals there will be a brief period of MVFR level ceilings between about 19/14Z and 19/20Z. Fog is reducing visibility to a half mile or less intermittently at the KHVR terminal and is expected to continue doing so until 19/10Z. At the KBZN, KEKS, and KHLN terminals between now and 19/20Z there is a 10 - 30% chance for a rain/snow mix. During the majority of this TAF Period there will be periodic mountain obscuration across Southwestern Montana. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 57 29 44 25 / 0 0 10 0 CTB 56 29 44 20 / 10 10 10 0 HLN 53 30 44 26 / 10 20 30 0 BZN 54 30 46 25 / 0 20 20 0 WYS 43 26 43 23 / 20 10 30 10 DLN 52 29 48 27 / 0 10 10 0 HVR 48 27 43 19 / 10 10 10 0 LWT 57 27 42 24 / 0 10 10 0

TFX WATCHES/WARNINGS/ADVISORIES

None.