textproduct: Great Falls

KEY MESSAGES

- Two waves of impactful snowfall develop this weekend into Monday as temperatures trend significantly cooler across the region.

- Initial concern through the day today and into tonight will be along the Rocky Mountain Front and across Central Montana.

- Concern for heavy snowfall expands further south into Southwest Montana Sunday into Sunday night.

DISCUSSION

/Issued 127 AM MDT Sat Oct 10 2026/

- Meteorological Overview:

A complex evolution to the upper level pattern will ensue today, initially with a large upper level trough with multiple embedded vort maxes sinking southward from the Pacific Northwest, elongating as it does so. At the surface an area of low pressure centered in southern SK is propelling a cold front southward across the plains early this morning. The combination of this front, favorable forcing, and ample moisture will result in a round of precipitation developing through the day today. Initial precipitation type looks to be rain in many areas before cold air advection near the surface wins out and flips precipitation type to snow. Confidence is highest in snow developing early near the Southern Rocky Mountain Front, where a band of snow will aid in flipping precip type to snow by early afternoon. Snow characteristic looks to be the wet and heavy variety, especially at lower elevations, which raises concern for trees with leaves on them still seeing snapped branches, potentially impacting power lines.

Colder air continues to sink southward into Southwest Montana heading into Sunday, though there remains some uncertainty with respect to just how far it makes it. Aloft the complex evolution continues, with the upper level troughing elongating further, while also interacting with the remnants of Rachel as they lift northeastward ahead of the trough axis. Ample moisture associated with not only the main troughing, but the remnants of Rachel will support the expansion of precipitation southward into Southwest Montana during the day Sunday as an upper level jet moves overhead. The extent of impactful snowfall across Southwest Montana will follow where the coldest air both aloft and at the surface ends up settling. Banded precipitation looks to persists into Monday morning across portions of Central and Southwest Montana before subsiding through the day.

The region looks to dry out for at least a couple days as the upper level troughing consolidates once again across the desert Southwest. Uncertainty grows a bit toward Thursday, though the majority of ensemble members remain dry Thursday toward the weekend. -AM

- Forecast Confidence & Scenarios:

Given marginal thermodynamics at times with respect to both the atmosphere and surface temperatures, it makes for quite the tricky snowfall/accumulation forecast. Overall there were no changes with this forecast cycle to ongoing winter highlights, but consideration was given to upgrades in a few areas:

- Northern Rocky Mountain Front and adjacent plains: This area looks to have the most consistent thermodynamic environment supporting snow (Cold throughout), but the greatest forcing looks to remain further south. Given snowfall amounts vary quite a bit from north to south across these zones, the Winter Weather Advisory was left as is. Should amounts increase much in these zones, a Winter Storm Warning may become necessary.

- Helena Valley: The greatest uncertainty in the Helena area is with respect to just how quickly precipitation flips over to snow today/this evening. Either way, initial snow that falls will need to overcome warm pavement to begin accumulating, which looks questionable through late tonight given uncertainty with respect to snowfall rates. Colder air continues to make inroads Sunday which will allow for greater snowfall rates to result in more accumulations. Given marginal snowfall forecast totals, I elected to continue with the Winter Weather Advisory for now.

- Near and south of I-90 Sunday into Sunday night: Ample forcing and moisture moving in within a deep fetch of southwesterly flow aloft (Supported by Rachel's remnants) will foster some banded precipitation Sunday into Monday. The area of greatest concern would be along and south of a line from Dillon to Bozeman for the greatest precipitation amounts. This also happens to be the area of greatest uncertainty with respect to the colder air at the surface and aloft. Given there are Winter Weather Advisories in place already, and that there is still uncertainty with respect to temperatures, no upgrades to a Winter Storm Warning were made. This area will bear monitoring for any trends over the next 24 hours or so. -AM

AVIATION

10/12Z TAF Period

Initial concern this TAF period will be for a front moving southward across the region, bringing precipitation and low clouds. Meanwhile further south across SW MT, a few showers have already resulted in a few wind gusts near 40 kts. While these gusts look to be isolated, they are still worth a mention. Additional instability may also result in a few thunderstorms this afternoon across SW MT.

Precipitation slowly spreads southward through the day today, transitioning to snow as colder air moves in. Mountains will become increasingly obscured through the TAF period. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 42 28 33 25 / 90 100 100 90 CTB 36 25 32 21 / 60 80 100 80 HLN 48 28 34 25 / 90 100 100 100 BZN 59 30 35 25 / 80 90 100 100 WYS 56 33 44 27 / 80 100 100 100 DLN 60 28 33 23 / 60 80 100 100 HVR 49 28 39 25 / 70 80 100 90 LWT 50 29 34 25 / 90 100 100 100

TFX WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning from 6 PM this evening to 6 AM MDT Monday for Big Belt, Bridger and Castle Mountains-Cascade County below 5000ft-Eastern Pondera and Eastern Teton-Elkhorn and Boulder Mountains-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Meagher County Valleys-Snowy and Judith Mountains.

Winter Weather Advisory from 6 PM this evening to 6 AM MDT Monday for Bears Paw Mountains and Southern Blaine-Beaverhead and Western Madison below 6000ft-Canyon Ferry Area-East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera- Eastern Toole and Liberty-Fergus County below 4500ft-Gallatin Valley-Gallatin and Madison County Mountains and Centennial Mountains-Helena Valley-Madison River Valley-Missouri Headwaters- Northern High Plains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Western and Central Chouteau County.

Winter Storm Warning from noon today to 6 AM MDT Monday for Gates of the Mountains-Southern High Plains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.