textproduct: Great Falls

KEY MESSAGES

- The potential for a widespread strong to 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, increased mountain snow, and lower elevation shower activity.

DISCUSSION

/Issued 313 AM MDT Mon Apr 6 2026/

- Meteorological Overview:

Low level easterly flow, associated with a 1040 MB surface high over the Canadian prairies, will continue for another day. Temperatures will be seasonably cool for northern areas and slightly above average in the south. Aside from a spotty shower over central and southwest MT this afternoon, mostly dry conditions will prevail.

On Tuesday, a compact Pacific trough and attendant cold front still looks to bring a period of strong gusty winds to much of the forecast area. An H700/H500 55 to 75 kt jet, supported by cold air advection still 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. Additionally, widely scattered convective shower activity will play a role in transferring stronger gusts to surface.

Despite lower and mid- level winds trending a bit lower per newer deterministic guidance, these factors still look to exert a greater impact than a typical event. The most persistent strong winds looking to occur along the Rocky Mountain Front and the plains along and west of the I15 corridor haven't changed much with max gusts topping out in the 75 to 90 mph range. 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 and even into Wednesday morning.

Light mountain snow and lower elevation scattered rain and snow shower activity develop on the backside of this system Tuesday night into Wednesday. Temperatures will also dip below average for a day or so following the cold frontal passage before milder conditions move in heading into the weekend. Another trough approaches the Northern Rockies and brings more widespread mountain snow and lower elevation shower activity for the Sunday through next Tuesday timeframe. - RCG

- Forecast Confidence & Scenarios:

Strong to intense winds on Tuesday...

Despite some deterministic models recently trending a bit lower with lower and mid- level winds, surface winds will be complimented by deep layer mixing thanks to the higher April sun angle in addition to the stronger winds phasing well with peak diurnal mixing. Climatological anomaly indices continue to latch on this event being unusually strong, especially for the beginning of April. ECMWF EFIs with respect to wind gusts continue to boast an impressive 0.8 to 0.99 across much of southwest through north- central MT, 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.

Confidence for the most persistent higher end 70 to 90 mph wind gusts are still mostly along the Rocky Mountain Front and the plains along and west of I15. Other areas may also instances of gusts to 75 mph, just not quite as widespread or frequent. Impacts will include difficult to dangerous travel conditions for high profile or light weight vehicles, localized visibility reductions from blowing dust, and instances of infrastructure/tree damage. The highest concern for semi roll overs will be along I15 from Shelby to the Canadian border and the highway 89 corridor roughly from Fairfield to the Canadian border. Farther south, a period of elevated fire weather conditions may develop for central/southwestern areas roughly south of the US highway 12 corridor. The timing of the greatest impacts still look to be in the late morning hours through early afternoon along the Rocky Mountain Front and the plains west of I15 while areas to the south and east see more impactful conditions later in the afternoon or even Tuesday night/Wednesday morning in the case of Fergus and the Bear's Paw zones.

Most of the high wind watches were upgraded to high wind warnings. The only exception to this was continuing the watch for Fergus and the Bear's Paw zones. There is lower confidence for these zones given the peak winds occurring during overnight hours Tuesday night. I did extend the end time of this watch to noon on Wednesday to cover lingering windy conditions Wednesday morning. The trend of leaving the Bozeman area and the higher terrain of Madison and Gallatin counties with no wind products continued with this forecast package. Stronger winds in these areas will be dependent on momentum transfer from convective shower activity and the cold front itself. This will continue to be monitored for increasing trends in regards to wind speeds and or duration. - RCG

AVIATION

06/12Z TAF Period

Scattered to broken low VFR clouds will continue over north- central MT through around 06/20Z. Easterly breezes will continue for most locations along and north of I90 with light and variable winds to the south. Southwest to westerly winds begin increasing along the Rocky Mountain Front after 07/06Z before strengthening and expanding to all areas on Tuesday. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 57 41 63 27 / 0 10 10 30 CTB 54 36 55 22 / 0 0 40 30 HLN 63 40 64 29 / 10 10 10 10 BZN 62 35 67 27 / 10 10 20 20 WYS 59 26 58 24 / 10 10 30 20 DLN 65 37 65 27 / 10 0 0 0 HVR 52 31 63 27 / 0 10 20 30 LWT 50 34 65 25 / 10 10 30 30

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning from 3 AM to 9 PM MDT Tuesday for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera- Northern High Plains-Southern High Plains-Southern Rocky Mountain Front.

High Wind Warning from 9 AM to 9 PM MDT Tuesday 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 Wednesday morning for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Snowy and Judith Mountains.