textproduct: Great Falls

KEY MESSAGES

- Strong and gusty winds develop once again from the late morning through early evening hours today.

- Another significant wind event is possible from Wednesday night through Thursday night.

- Heavy mountain snowfall is possible from the end of the work week to through the first half of the weekend, especially over the Continental Divide.

DISCUSSION

- Meteorological Overview:

A very active and unsettled pattern characterized by persistent quasi-zonal flow with embedded waves rippling eastward will bring daily chances for precipitation, seesawing temperatures, and numerous days of strong to potentially high winds.

Of particular concern will be the period from Wednesday afternoon/evening through Saturday morning/afternoon when a plume of Pacific moisture will stream eastward and over the Northern Rockies. This plume of Pacific moisture will bring heavy mountain precipitation, primarily in the form of snow, and strong winds, particularly from Wednesday night through Friday morning. A cold front moving south over the plains of Central and North Central Montana Thursday night/Friday morning will stall near the Central Montana Island Ranges. Pacific moisture streaming over this stalled low to mid-level front will provide the focus for precipitation to end the work week and into the first half of the upcoming weekend for most of the plains of Central and North Central Montana. Further to the south across the valleys/mountains of Central and Southwest Montana periods of mountain snow and strong valley winds will occur over the same period, with temperatures running some 10 to nearly 20 degrees warmer than over the plains of Central and North Central Montana. - Moldan

- Forecast Confidence & Scenarios:

Strong to potential High Winds today (Monday)...

Anomalously strong westerly flow, with H700 winds of between 40- 50kts, will provide additional opportunities for strong and gusty winds over portions of Southwest through North Central Montana. ECMWF EFIs of between 0.5-0.8 support a climatologically unusual period of windy conditions through the day today, with BUFKIT sounding supporting that the strongest winds will occur from the late morning through early evening hours (i.e. 16z to 02z). NBM25Pct wind gusts values, which represent a reasonably low end wind gusts scenario (75% chance for higher wind gusts or a 25% chance for lower wind gusts), support gusts of between 35-45 mph across Southwest through North Central Montana; with NBM75Pct wind gusts values, which represent a reasonably high end wind gusts scenario (75% chance for lower wind gusts or a 25% chance for higher wind gusts), support gusts of between 45-60 mph. While the NBM75Pct values suggest that a few locations could reach or exceed high wind criteria current thinking is that these instances would be limited to a few locations per county. For this reason we will hold off on issuing any High Wind Warnings for the day today; however, should wind gusts exceeding criteria become more widespread than current thinking then a short term High Wind Warning may be needed.

High Winds from Wednesday night through Friday morning...

Another widespread and long duration wind event continues to be of concern over the period, with H700 winds per NAEFS analysis ranging from 3 to 5 standard deviations above normal at between 50-90kts. These wind values, particularly along and south of the MT Hwy 200 corridor, are outside of the CFSR climatology between 06z-18z Thursday. ECMWF EFIs in excess of 0.8 support the potential for this wind event to be very unusual to extreme (i.e. somewhat similar to December 17, 2025 and March 8, 2026). Right now one good thing within the ECMWF EFIs is the fact that the shift of tails (SOTs), which would indicate how extreme the top 10% of ensemble membership is, only has a value of 1. Should these shift of tails climb further over the succeeding days then a truly extreme and impactful wind event would be possible. Given the recent strain infrastructure and vegetation this event has the potential to be particularly damaging.

Accumulating Snow from Wednesday evening through Saturday afternoon

The potential for heavy, significant snowfall along the Continental Divide north of the Montana Hwy 200 corridor continues to be of concern as a plume of Pacific moisture streams eastward over the Northern Rockies. ECMWF EFIs in excess of 0.95 exist nearly every day, with a shift of tails of 3 contouring these areas. NBM25Pct (reasonably low end) values with respect to snowfall accumulations along the Continental Divide from 00z Thursday through 00z Saturday range from 1 to nearly 3 feet, with NBM75Pct (reasonably high end) values ranging from 3 to 5 feet. Over the plains of Central and North Central Montana 25Pct values range from 2 to 4 inches while the 75Pct ranges from 8 to 12 inches. Snow levels and where the cold front stalls will ultimately impact lower elevation snowfall to end the work week. - Moldan

AVIATION

09/06Z TAF Period

The cold front currently pushing south across North-Central MT will continue to produce scattered snow showers/bands through Monday morning. MVFR/IFR clouds and vis continue with snow showers, with vis to dropping below a mile at times across North- Central MT. After precipitation exits Monday morning, breezy to gusty winds move back in for Monday afternoon. There will be lingering snow showers Monday afternoon, but will be hit or miss at terminals in North-Central MT. -Wilson

PRELIMINARY POINT TEMPS/POPS

GTF 43 19 39 22 / 30 10 30 10 CTB 36 13 33 20 / 40 20 30 0 HLN 46 19 37 20 / 30 30 40 0 BZN 46 19 36 14 / 50 20 40 10 WYS 44 18 30 3 / 20 10 50 10 DLN 48 18 35 14 / 10 10 30 0 HVR 41 16 39 18 / 40 30 30 10 LWT 39 17 35 17 / 50 10 60 20

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until noon MDT today for East Glacier Park Region-Southern Rocky Mountain Front.

Winter Weather Advisory until 9 AM MDT this morning for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft- Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Fergus County below 4500ft-Hill County-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Northern Blaine County- Northern High Plains-Snowy and Judith Mountains-Southern High Plains-Western and Central Chouteau County.