textproduct: Great Falls

KEY MESSAGES

- Mainly mountain precipitation over the next couple days.

- Canadian cold front brings much colder temperatures, especially to the Hi-Line, beginning late Friday night lasting into Sunday morning.

- Drier and milder conditions then develop heading into much of next week.

UPDATE

/Issued 831 PM MST Thu Dec 25 2025/

Satellite imagery this evening shows several waves of moisture tracking into the Northern Rockies ahead of a deep/occluded upper low/trough approaching northern CA. Showers across western MT and ID will continue to track east tonight with the next embedded wave, bringing a period precipitation to areas along the continental divide later tonight with a few isolated to scattered showers tracking east of the divide across north-central and SW MT. Meanwhile, orographically forced precipitation in moist SW flow aloft increases along the divide near Yellowstone NP, bringing steadier precipitation there tonight through much of the day Friday, primarily concentrated near the ID/WY border. Snow levels initially near 6000 ft this evening will gradually lower to around 5000 ft by Friday morning as cooling aloft occurs ahead of the advancing upper trough. A shallow cool/moist airmass lingers at elevations below around 3000 ft across portions of north-central MT where surface temps remain near to just below freezing. Areas of fog and low clouds are the primary concern in these areas through the overnight period, though some brief/light freezing precipitation is possible if/where isolated rain showers develop later tonight. Hoenisch

DISCUSSION

/Issued 831 PM MST Thu Dec 25 2025/

- Meteorological Overview:

Through Friday afternoon:

Southwest flow aloft continues across the region this afternoon ahead of weakening upper level troughing off the Pacific coast. Several waves ejecting from this trough will move across the Northern Rockies over the next 24 hours or so, resulting in periods of mainly mountain precipitation. Snow looks most impactful near the West Yellowstone area tonight into Friday, transitioning to the Rocky Mountain Front late Friday morning into Friday night. Winter Weather Advisories have been issued for these areas. While there remains a low (20% or so) probability for light freezing rain near the Canadian border tonight and again Friday afternoon, the risk appears too isolated at this point to warrant a Winter Weather Advisory.

Rather steep lapse rates across portions of Southwest through Central Montana will aid in translating a belt of stronger mid-level southwest flow to the surface Friday afternoon. While widespread high winds are not forecast, at least a few instances are likely at ridgetops and in north south oriented valleys. Worth noting is that guidance that leans toward cooler temperatures aloft does result in marginal instability. If showers are able to form they would also assist in mixing stronger winds to the surface. A few lightning strikes cannot be ruled out Friday across portions of Southwest and Central Montana.

Friday Night into Sunday morning:

While the troughing off the Pacific coast continues to weaken, a more potent wave diving southeastward from BC will propel a Canadian cold front across the region from north to south from late Friday night into Saturday. Ahead of this front there looks to be a period of snow showers that cross the Continental Divide late Friday night into Saturday morning. Confidence in exact location of higher snow amounts with these snow showers was too low to warrant a Winter Weather Advisory at this time.

High temperatures for many areas will occur early in the day, falling through the afternoon into the evening behind the aforementioned Canadian cold front. Ambient temperatures by Saturday evening and Saturday night look to drop to below -20F near the Canadian border. Snow looks to accompany the Canadian cold front, with the greatest snow amounts in the mountains and in northerly upslope areas.

Sunday into next week:

Upper level troughing begins exiting eastward Sunday morning ahead of a building ridge across the far eastern Pacific. This ridge largely looks to remain in place through early to middle of next week, which would keep a northwest flow aloft intact across the Northern Rockies. While this normally isn't particularly conducive to mild temperatures, temperatures do look to trend warmer Sunday and into next week. The anti-cyclonic nature of the flow aloft will keep the region largely dry Sunday into much of next week. -AM

- Forecast Confidence & Scenarios:

Through Friday afternoon:

The greatest piece of uncertainty is with respect to additional instances of freezing rain across the Hi-Line tonight and again tomorrow. Should any precipitation develop near the Havre area, surface temperatures look to be sufficiently cool to result in a few instances of freezing rain.

Additional uncertainty comes in regarding wind gust potential across Southwest Montana into portions of Central Montana. Mid level flow is potent, but forecast soundings do not look to reliably mix the strongest winds to the surface. Should any showers end up developing (Most aggressive guidance shows some instability), the risk for strong wind gusts would increase. Those with outdoor plans across Southwest Montana and adjacent areas should be prepared for gusty winds Friday either way.

Friday night:

Confidence is high that snow showers will develop along the Continental Divide Friday night into early Saturday ahead of the Canadian cold front. Confidence wanes however with respect to the exact location of where more persistent snow shower activity will ultimately develop. Some areas along the Continental Divide from MacDonald Pass southward will need Winter Weather Advisories should confidence increase in specific areas seeing more persistent snow showers.

Saturday along and behind the cold front:

Confidence is high in the colder temperatures arriving from north to to south late Friday night into Saturday morning across the region. Where there is less model consensus is with respect to snow across lower elevations. Pattern recognition suggests that northerly upslope areas should see at least light snow accumulations from this front, with other areas at lower elevations seeing at least a few hour period of light snow along and behind the Canadian front. Guidance so far has been a bit more bearish on amounts and quick to decrease the probability for snow. At this point the probability for an inch of snow over lower elevations is quite low, 20% or less in most areas. Trends will be closely monitored with respect to snow amounts over the next day or so. -AM

AVIATION

26/06Z TAF Period

VFR conditions are expected to prevail for all sites except KHVR through the period. The first wave of precipitation will move into the region through the first 6 hours of the period with coverage generally expected to be isolated enough to not impact any of the terminals. The second wave of precipitation will arrive Friday afternoon and become more widespread heading into Saturday morning. The cold front arriving Friday evening will bring much cooler temperatures behind it with the potential for mountain snow and a lower elevation rain/snow mix. Mountain obscuration will remain a concern through the entire TAF period and especially after 26/18Z as the second wave of precipitation arrives.

The only site that is expected to deal with fog through the overnight hours is KHVR. Earlier, 8 to 10kt winds proved just strong enough to mix out the fog leaving KHVR clear over the past couple hours. This trend is expected to continue through 26/08Z but with winds remaining calm under clear skies and increasing humidity there is an expectation that fog will redevelop through the overnight hours. When exactly the fog ends has been a little uncertain but right now the best confidence is in visibility improving by 26/12Z. There is a chance that fog could linger in the area through 26/18Z but confidence was not high enough at this time to include it in the TAF. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 39 50 8 17 / 20 20 20 80 CTB 23 37 -3 6 / 10 20 20 50 HLN 33 47 22 27 / 30 30 50 60 BZN 33 48 24 32 / 30 30 30 70 WYS 28 35 19 24 / 90 90 70 90 DLN 32 43 23 28 / 30 30 20 40 HVR 23 36 4 13 / 20 30 20 50 LWT 37 50 12 25 / 20 10 10 70

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 8 AM Friday to 2 PM MST Saturday for East Glacier Park Region-Southern Rocky Mountain Front.

Winter Weather Advisory from 2 AM to 6 PM MST Friday for Gallatin and Madison County Mountains and Centennial Mountains.

High Wind Warning from 10 AM to 6 PM MST Friday for Madison River Valley.