textproduct: Great Falls

KEY MESSAGES

- After relatively dry conditions during the day today another wave of light snow is expected to return tonight and into the day on Wednesday across Southwest and Central Montana.

- Better chances for impactful snow arrive on Thanksgiving across Central and North Central Montana, with snow lingering through the day on Friday as a strong cold front moves south through Montana.

- Coldest air of the season so far will arrive this weekend.

DISCUSSION

/Issued 251 AM MST Tue Nov 25 2025/

- Meteorological Overview:

Relatively dry condtions are expected through the daylight hours today beneath northwesterly flow aloft in wake of the departing disturbance; however, isolated snow shower can't be ruled out over and near the mountains north of the US Hwy 12 corridor. Temperatures will be some 5 to 15 degrees colder than that of Monday, with light southerly winds. By this evening an embedded wave within the northwest flow will quickly dive southeast from over British Columbia and the Pacific Northwest and over Southwest and Central Montana through Wednesday morning. This quick moving wave will bring light snowfall to the valleys of Southwest and Central Montana, with generally 1-3" for the passes and upwards of 6" to the higher peaks.

On Thursday transient ridging ahead of a shortwave digging into the Pacific Northwest will begin to slide towards the Northern Rockies, with a mid-level warm front lifting from southwest to northeast over Southwest through North Central Montana. Pacific moisture and lift associated with the warm front will overrun the colder air near the surface during the day Thursday, which will help to support a band of snow lifting north across the Northern Rockies. This band of snow looks to be "most" intense along and north of the Montana Hwy 200 corridor, but even areas northeast of a Helena to Bozeman line are likely to see some snow. The aforementioned shortwave digging into the Pacific Northwest will continue to dig southeast towards the Central Rockies through Friday morning, with a strong cold front surging south across Montana through the day on Friday. This cold front and the upper level disturbance will bring additional opportunities for snow to most locations across Southwest through North Central Montana, especially to the plains of Central and North Central Montana and northerly upslope areas of Southwest, Central, and North Central Montana. Cold air will also filter south in wake of the cold front bringing the coldest air of the season so far for the weekend. - Moldan

- Forecast Confidence & Scenarios:

Accumulating Snow from late tonight through Wednesday...

A fast moving disturbance within northwest flow will bring a quick 1- 3" of snow to mountain passes along and south of the Montana Hwy 200 corridor and north of a Chief Joseph to West Yellowstone line, and 3- 6" to the higher peaks. Most valley locations are likely to see less than 1" of snow, with the exception of the eastern Gallatin Valley (i.e. western/northern foothills of the Bridger and Gallatin Ranges) where HREF probabilities support a 60+% chance for 1" or more of snow and a 20-40% chance for 2" or more snow. For now no Winter Weather Advisories have been issued given the borderline amounts and timing of the snow (i.e. 1/3rd of the snow will fall during the lower traveled overnight hours tonight), but given that this is the Thanksgiving travel week future shifts may consider highlights.

Accumulating Snow Thursday through Friday evening...

ECMWF EFIs with respect to snow, which signify the potential for a climatologically unusual (values of between 0.5 to 0.8) or very unusual to extreme (values of 0.8+) snow event, along and north of the US Hwy 12 corridor remain (from the past 24 hours) in excess of 0.5 from the evening hours of Thanksgiving through the day on Friday, with values now (latest) ranging between 0.6 to 0.7 over much of the plains of Central and North Central Montana. Additionally, NBM4.3 probabilities for 4" or more of snow over the plains of Central and North Central Montana generally range from a 10-30% chance, which are relatively unchanged over the past 24 hours. Probabilities for 6" or more of snow over this same timeframe range from a 30% chance across the Island Ranges of Central Montana to between a 60-80% chance along the Continental Divide north of the Montana Hwy 200 corridor, with a 30-50% chance for 12" or more of snow across the same locations of the Continental Divide. Given that the snow will begin falling during the day on Thursday and persist into the day on Friday this event has the potential to disrupt a busy time for holiday travel. What is becoming more concerning in addition to the falling snow will be the potential for blowing/drifting snow Thursday night through Friday morning along and west of the I-15 corridor over the plains of Central and North Central Montana. By Thursday evening a barrier jet, with H850 wind speeds of 20-30kts, will begin to slide south along the Rocky Mountain Front. These strong boundary layer winds combined with the falling snow may present a scenario where significant reductions in visibility occur for travelers on the US Hwy 89 and I-15 corridors northwest/north of Great Falls. Future winter weather highlights will be needed should trends hold.

Cold Temperatures Friday through Sunday...

Guidance is beginning to come into better agreement with the timing of the cold air arriving to the Northern Rockies on Friday/Friday night as an Arctic front dives south from Canada. What remains unclear is how cold temperatures actually fall through the weekend, which is mainly due to uncertainty on how much snow falls prior to and with the passage of the cold front. Should most locations see several inches of snowfall from Thursday through Friday then there is a better chance for temperatures to be much colder than currently forecasted. - Moldan

AVIATION

25/12Z TAF Period

IFR/MVFR conditions due to low CIGS and/or reduced VIS from fog will continue to be of concern over the KHVR, KGTF, and KLWT terminals through 15z this morning. Otherwise VFR conditions will prevail through 06z Wednesday, with lowering CIGS southwest of a KHLN to KBZN line beyond 21z this afternoon as an upper level disturbance approaches the Northern Rockies. Snow will then begin to overspread portions of Central and Southwest Montana after 06z Wednesday, with CIGS lowering further at the KHLN, KBZN, and KEKS terminals. Mountains will be obscured through this morning, and then once again from this evening through Wednesday. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 36 26 39 25 / 0 20 30 10 CTB 31 15 33 16 / 0 10 20 10 HLN 33 25 37 28 / 0 40 50 20 BZN 33 22 38 25 / 0 50 70 20 WYS 27 14 31 19 / 0 60 90 30 DLN 33 23 42 27 / 0 20 20 10 HVR 29 11 27 10 / 20 0 10 0 LWT 34 19 34 22 / 0 10 30 10

TFX WATCHES/WARNINGS/ADVISORIES

None.