textproduct: Great Falls

KEY MESSAGES

- Shower and thunderstorm activity continues to expand northeastward this afternoon and gradually transitions to areas of widespread rain and snow tonight.

- Snow and gusty to strong northwesterly winds become more widespread tonight into Thursday, with the greatest impacts, including brief whiteout conditions, over the Little Belt Mountains and their northwest facing foothills Thursday morning.

- Another round of accumulating snow develops Thursday night into Friday morning, mostly impacting areas along the Continental Divide and southwest Montana.

- Cooler and unsettled conditions continue this weekend, with temperatures warming closer to average by early next week.

DISCUSSION

/Issued 525 PM MDT Wed Apr 22 2026/

- Meteorological Overview:

Deep southerly flow aloft continues to bring gusty to strong winds over southwest and portions of central MT this afternoon, especially over the narrow south to north oriented C/SW valleys and exposed ridge tops. Shower and thunderstorm activity will continue increasing from the southwest this afternoon with localized wind gusts being the primary hazard due to momentum surface transfer from 30 to 50 kt H700/850 flow. The colder air aloft moving in will also support some instances of small hail with the stronger cores. Convergence of low level winds in advance of the approaching trough may even initialize an isolated and weak cold air funnel cloud, mostly along the Continental Divide and over southwest MT. Mild Temperatures this afternoon quickly transition to chilly and wet conditions this evening and tonight following a cold frontal passage.

Precipitation becomes widespread this evening and tonight as a trowel develops on the northwest side of the mid- level low. H700 temperatures becomes cold enough for snow at all elevations over central/north-central and southwest MT by Thursday morning, though snowfall amounts and overall impacts still look to be greatest over the north/northwest facing foothills of the central island ranges where gusty northwesterly winds and snow will overlap. Other areas that will observe accumulating snow impacts include areas along the Continental Divide and over the higher terrain of southwest MT. The snow will become more scattered and convective in nature during the day on Thursday while diurnal heating begins to ease impacts. Forty to 50 kt H850 flow wrapping around the low pressure system will bring gusty to strong northwesterly surface winds along the Hi-Line and plains east of I15 tonight into Thursday, especially on the south/southeast downslope areas of the Sweetgrass Hills, Bear's Paw, and Snowy Mountains.

A secondary shortwave moves in Thursday night into Friday and brings additional snow and snow shower activity. Although models have lost interest in a smaller scale closed circulation developing over the southwest, H500/H700 temperatures around (-30C/-15C) and sufficient frontogenesis will be supportive of accumulating snow at all elevations along the Continental Divide and southwest MT. Cold and moist northwesterly flow aloft will also initiate some periods of less impactful light snow for most locations Friday into Saturday, especially along the Hi-Line. Broad troughing continues through the weekend and gradually transitions to a northwesterly flow aloft next week as ridging attempts to develop along the Pacific coast. This will maintain daily opportunities of rain/snow shower activity, especially for areas over or near higher terrain. Temperatures will slowly trend towards the seasonal average by early next week. - RCG

- Forecast Confidence & Scenarios:

Snow and winds through Friday...

The threat for strong south/southwesterly surface winds over the narrow south to north oriented C/SW valleys and exposed ridge tops decreases by this evening as will the threat for localized convective wind gusts and isolated instances of small hail along the the leading edge of showers and thunderstorms. This will shift the focus to snow and wind impacts tonight through Friday morning.

Cold northwesterly flow on the backside of the low pressure system will quickly ramp up the snow and surface winds tonight into Thursday. Northern areas will initially be most impacted, especially over and near the central island ranges where the combination of winds over 50 mph and heavy wet snow wet snow look to cause instances of power outages and tree damage in addition to brief whiteout conditions. The impacts will be slightly less for other mountain areas, though snow will become moderate to heavy over and near the Madison and Gallatin by Thursday morning. Uncertainty remains high in terms of lower elevation impacts, especially over the plains and in the Gallatin Valley. In the mountains, the uncertainly was primarily in regards to blizzard conditions in the Little Belts and the nearby northwesterly foothills, especially in the Geyser area. The wet texture of the snow should preclude extended periods of whiteout conditions, though there looks to be at least isolated power outages and tree damage. Winter impacts begin to ease heading towards the afternoon hours with the snow becoming more scattered in nature and the commencement of diurnal heating.

The winter storm watches for the Little Belt's and Judith basin lower elevations were upgraded to warnings. Also advisories were added for the Helena Valley and Cascade County. An area of frontogenesis sets up between Helena and Great Falls and may bring locally heavy snow totals up to around 4 to 6 inches. Note that there will be a sharp gradient with some areas seeing little to no snow at all. For example, the northern and western portions of Cascade County look to see negligible snowfall while the south and eastern portions see totals in excess of and associated impacts. Similarly the south and western portions of the Helena Valley will see the higher totals with lesser amounts elsewhere.

There will be be gusty to strong winds that develop over much of central/north-central MT tonight into Thursday driven by H700/850 40 to 60 kt northwesterly flow. The high wind watch was converted to a high wind warning and and will roughly encompass the same area with the exception of Chouteau County. Locations especially susceptible to sustained winds above 40 mph and gusts over 60 mph will be the southeast aspects for the Sweetgrass Hill, Bear's Paw, and the Snowy Mountains. With winds looking to start a little earlier, especially over the Sweetgrass Hills, the warning start time will be 9 pm this evening.

A secondary wave moves through Thursday night into Friday and delivers another round of snow, but with less wind. This one will mostly impact areas along the Continental Divide and southwest MT. Even though the expectations for a closed circulation over the southwest has fallen through, upper level temperatures will be much colder ensuring lower elevation snow accumulation efficiency. The winter storm warning for the Madison and Gallatin mountain zone was extended through noon on Friday. Nearly all lower elevations for the southwest were assigned winter weather advisories for Thursday night through Friday morning to cover the light to moderate impacts, this includes the Helena and Bozeman areas. - RCG

AVIATION

23/06Z TAF Period

For the first few hours of this TAF Period there will be isolated showers around the KHVR and KLWT terminals. At the KBZN, KEKS, and KWYS terminals between 23/18Z and 23/24Z there is a 10 - 20% chance for thunderstorms. During the majority of this TAF Period there will be rain and snow around the KBZN, KEKS, KWYS, and KHLN terminals with rain and snow around the KCTB, KGTF, KHVR, and KLWT terminals during the first half of this TAF Period. During the majority of this TAF Period there will be mountain obscuration across North- central, Central, and Southwestern Montana. Between now and 23/15Z there will be isolated instances of low-level wind shear and mountain wave turbulence across Southwestern Montana. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 29 41 26 39 / 100 70 40 50 CTB 26 40 22 35 / 90 30 20 40 HLN 29 39 24 40 / 100 90 60 70 BZN 31 42 21 40 / 100 90 70 70 WYS 24 37 17 37 / 100 90 80 80 DLN 32 43 25 40 / 90 80 70 60 HVR 30 44 25 38 / 80 30 10 50 LWT 28 37 21 35 / 100 60 20 50

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until 6 PM MDT Thursday for Bears Paw Mountains and Southern Blaine-Eastern Toole and Liberty-Fergus County below 4500ft-Hill County-Northern Blaine County-Western and Central Chouteau County.

Winter Weather Advisory until 6 PM MDT Thursday for East Glacier Park Region-Northern High Plains.

Winter Weather Advisory until 6 PM MDT Thursday for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Snowy and Judith Mountains.

Winter Weather Advisory until noon MDT Friday for Big Belt, Bridger and Castle Mountains-Elkhorn and Boulder Mountains-Gates of the Mountains-Helena Valley-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.

Winter Storm Warning until 6 PM MDT Thursday for Little Belt and Highwood Mountains.

Winter Storm Warning until noon MDT Friday for Gallatin and Madison County Mountains and Centennial Mountains.

Winter Weather Advisory until noon MDT Thursday for Cascade County below 5000ft.

Winter Storm Warning until 6 PM MDT Thursday for Judith Basin County and Judith Gap.

Winter Weather Advisory from 6 PM Thursday to noon MDT Friday for Beaverhead and Western Madison below 6000ft-Canyon Ferry Area-Gallatin Valley-Madison River Valley-Missouri Headwaters.