textproduct: Great Falls

KEY MESSAGES

- The potential for a widespread and intense wind event continues to grow for the day on Tuesday, with the most intense winds currently expected to occur along and west of the I-15 corridor.

- Light mountain snow and lower elevation rain and snow showers develop Tuesday night into Wednesday behind a cold front.

- Another trough looks to move in during the second half of next weekend for another cool down and increased shower activity.

DISCUSSION

/Issued 531 PM MDT Sun Apr 5 2026/

- Meteorological Overview:

Northwest to quasi-northwest flow aloft will remain over the Northern Rockies through Monday while a 1040 mb surface high moves southeastward out of Canadian prairies into northern plains. This will bring a moist easterly flow in the low levels for cloudier and cooler conditions, particularly for central and north-central MT. There may be some patchy fog and spotty light precipitation, though easterly breezes should reduce fog impacts some and precipitation amounts look to be negligible and mostly concentrated along the Hi-Line.

On Tuesday, a compact Pacific trough and attendant cold front will bring a period of strong gusty winds to much of the forecast area. An H700/H500 60 to 80 kt jet, supported by cold air advection, looks to pass through during late morning and afternoon hours when diurnal mixing is near its peak. There will also be mountain wave activity that will contribute to localized stronger gusts near areas of higher terrain. These factors will make this winds more impactful than a typical event. The most persistent strong winds look to occur along the Rocky Mountain Front and the plains along and west of the I15 corridor where max gusts in the 75 to 90 mph range will be common. Most of the winds will occur in the daylight hours with the exception of Fergus County and areas near the Bear's Paw Mountains. These locations will see their strongest winds later in the afternoon and continuing well into the overnight hours.

Light mountain snow and lower elevation scattered rain and snow shower activity will develop on the backside of this system with a short period of below average temperatures following the cold frontal passage. Milder conditions move in for next weekend before another trough passes through heading into early next week. While this system should bring some cooler temperatures and increased shower activity, confidence is low in regards to precipitation coverage and amounts due to a large portion of the said trough shearing off and moving southeast toward the Great Basin and southwestern conus. - RCG

- Forecast Confidence & Scenarios:

High Wind Potential on Tuesday...

Confidence continues to rise from shift-to-shift that high winds will occur on Tuesday across portions of Southwest, Central, and North Central Montana; however, the areal coverage of these high winds still remains uncertain and thus the High Wind Watches that were issued over the past 24 hours remain valid. Additionally, the High Wind Watch was expanded to include the Gates of Mountains, Helena Valley, Meagher County Valleys, and Elkhorn and Boulder Mountains zones. While these locations may see a shorter period of high winds as compared to other areas the potential intensity of these winds within a shorter period of time necessitated the further expansion of the High Wind Watch.

Run-to-run values within the ECMWF EFIs and NAEFS continue to increase, which is giving rise to increased confidence that a very unusual to potentially extreme high wind event, with respect to April climatology, may occur across portions of the Northern Rockies on Tuesday. ECMWF EFIs with respect to wind gusts have now reached an impressive 0.8 to 0.99 across much of Southwest through North Central Montana, with even a Shift of Tails (SOTs) of 1 now being observed across much of Central Montana. While a SOT of 1 appearing is not in itself impressive it is worth mentioning given the run-to- run tendency over the past 48 hours for values to increase. Additionally, EFIs with respect to sustained wind speeds now range from 0.6 to 0.9 across much of the same areas, which is concerning as a prolonged period of sustained high winds will stress infrastructure that has already been stressed over multiple wind events since October 2025. H700 winds per NAEFS analysis are forecasted to reach between 40-70kts on Tuesday, with return interval for these values occurring 1 day every 10 years during the first half of April climatology. This further helps to strengthen confidence in an impactful wind event, especially considering that the increasing April sun angle will contribute to deeper mixing as compared to during the heart of the winter season. As of right now deterministic guidance has the strongest mid-level winds and trough axis moving over Southwest through North Central Montana from the mid-morning hours on Tuesday through the afternoon hours, which should ensure that a portion of these winds mix down. Where exactly the core of strongest winds is at between 18-24z on Tuesday during peak mixing will ultimately determine where the most intense winds occur, but none-the-less other areas will still see strong winds.

The following table illustrates the NBM10Pct (Low End Scenario), NBM50Pct (Most Likely Scenario), and NBM90Pct (High End Scenario) for maximum wind gusts (mph) and sustained winds speeds (mph) for select locations across North Central, Central, and Southwest Montana :

24 Hour Maximum Wind Gusts LOCATION Low End | Most Likely | High End Browning 60 MPH | 75 MPH | 85 MPH Cut Bank 60 MPH | 70 MPH | 85 MPH Havre 45 MPH | 50 MPH | 65 MPH Great Falls 50 MPH | 60 MPH | 75 MPH Lewistown 40 MPH | 50 MPH | 60 MPH Helena 45 MPH | 60 MPH | 75 MPH White Sulphur Springs 45 MPH | 50 MPH | 65 MPH Bozeman 50 MPH | 55 MPH | 70 MPH Dillon 50 MPH | 60 MPH | 70 MPH Ennis 40 MPH | 50 MPH | 60 MPH West Yellowstone 35 MPH | 45 MPH | 55 MPH

24 Hour Maximum Sustained Wind Speeds LOCATION Low End | Most Likely | High End Browning 40 MPH | 50 MPH | 60 MPH Cut Bank 40 MPH | 50 MPH | 60 MPH Havre 30 MPH | 35 MPH | 45 MPH Great Falls 35 MPH | 45 MPH | 50 MPH Lewistown 25 MPH | 35 MPH | 40 MPH Helena 25 MPH | 40 MPH | 50 MPH White Sulphur Springs 25 MPH | 35 MPH | 40 MPH Bozeman 30 MPH | 35 MPH | 45 MPH Dillon 30 MPH | 35 MPH | 45 MPH Ennis 30 MPH | 40 MPH | 50 MPH West Yellowstone 15 MPH | 15 MPH | 20 MPH

- Moldan

AVIATION

06/06Z TAF Period

The initial concern this TAF period will be for some low clouds across North-central Montana through the morning Monday. VFR conditions prevail otherwise under mid and high-level cloudiness. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 29 57 41 63 / 0 0 10 10 CTB 26 54 36 55 / 0 0 0 40 HLN 34 63 40 64 / 0 10 10 10 BZN 32 62 35 67 / 0 10 10 20 WYS 24 59 26 58 / 0 10 10 30 DLN 34 65 37 65 / 0 10 0 0 HVR 29 52 31 63 / 0 0 10 20 LWT 28 50 34 65 / 10 10 10 30

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Watch from Tuesday morning through Tuesday evening for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains-Southern High Plains- Southern Rocky Mountain Front.

High Wind Watch from Tuesday morning through Tuesday evening for Beaverhead and Western Madison below 6000ft-Big Belt, Bridger and Castle Mountains-Cascade County below 5000ft-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Elkhorn and Boulder Mountains-Gates of the Mountains-Helena Valley-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Madison River Valley-Meagher County Valleys-Northwest Beaverhead County- Upper Blackfoot and MacDonald Pass-Western and Central Chouteau County.

High Wind Watch from Tuesday afternoon through late Tuesday night for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Snowy and Judith Mountains.