textproduct: Great Falls

KEY MESSAGES

- Windy conditions develop today in advance of a cold front, particularly over Southwestern Montana.

- Widely scattered showers and even a rumble of thunder may accompany the front late this afternoon.

- The cold front brings widespread snowfall to all elevations tonight into Thursday, though accumulating snow impacts will mostly be over and near areas of higher terrain.

- Temperatures fall well below the seasonal average Thursday and Friday, with another round of scattered light snows on Friday.

- A building upper level ridge of high pressure will bring a return to milder and dry conditions before unsettled conditions return next week.

DISCUSSION

/Issued 516 AM MDT Wed Apr 15 2026/

- Meteorological Overview:

North-central, Central, and Southwestern Montana will be on the western edge of an upper level ridge today, resulting in southerly flow aloft. This will bring slightly warmer temperatures to the area, as well as another day of windy conditions in Southwestern Montana. Instability will also increase, resulting in the potential for isolated locations to hear a rumble of thunder in the afternoon. The Rocky Mountain Front will see snowfall throughout the day, with heavier amounts in the higher elevations. As the ridge continues to move east, an upper level trough will begin to move in from the west coast, bringing an increase in atmospheric moisture. This evening into tonight a cold front will push down from the north, lowering temperatures. The cooler temperatures combined with increased moisture will bring snow showers along the I-90 Corridor late this afternoon into the early evening. North-central and Central Montana will begin to see rain showers in the evening, transitioning to more widespread snow during the overnight hours. Snowy/slushy roads will be most prevalent Thursday morning. Well-below seasonal average temperatures will be seen across North-central, Central, and Southwestern Montana on Thursday, in thanks to the upper-level trough deepening over the Great Basin and the cold front.

On Friday, North-central, Central, and Southwestern Montana remain under the influence of the upper-level trough. This will cause temperatures to remain on the chillier side with lows in the teens and another round of snow showers Friday morning. As the trough moves to the east, an upper level ridge of high pressure to the west begins to build, allowing temperatures to warm in the afternoon and precipitation chances to decrease. The upper level ridge will move east over Montana on Saturday and Sunday and bring milder and drier weather across the region. Early next week the benign conditions continue until troughing brings increased shower activity by the middle of next week. - Dzomba

- Forecast Confidence & Scenarios:

Gusty to strong winds over southwest MT today...

A 30 to 50 kt H700 southwesterly jet will develop over southwest MT in advance of the approaching trough and cold front. Stronger end surface winds will be most pronounced over the narrow south to north oriented valleys and the exposed mountain peaks south of the I90 corridor. Criteria winds/gusts (40 mph/58 mph) look to be most widespread in the late afternoon and early evening hours when diurnal mixing, widely scattered convective showers, and the cold front itself will all promote at least a brief period of surface momentum transfer. Climatological anomaly indices continue to highlight this event with the ECMWF EFI sustained wind speed still generally ranging from 0.6 to 0.8 for the aforementioned locations, while gusts remain slightly higher at 0.7 to nearly 0.9. With this in mind the high wind watch for the Madison Valley and Beaverhead/W Madison lower elevations will be upgraded to a warning. The only change to the timing will be to extend it into the evening to cover the frontal passage and associated convection/momentum transfer.

Widespread snow tonight into Thursday...

Light snow will continue to increase today along the immediate eastern slopes of the Rocky Mountain Front as moisture increases H500 heights fall. Once the cold front clears the region this evening, the cold core aloft will be sufficient to support a period of widespread snow at all elevations tonight into Thursday. Impactful accumulations will generally be confined to areas over and near higher terrain, including the Rocky Mountain Front, the central island ranges, and the Madison/Gallatin mountains.

Winter weather advisories were added to include most mountain areas. The winter storm watch continues for the Madison/Gallatin ranges and now runs through midnight Friday rather than the previous 6 am Friday morning expiration time. The cold north/northwesterly upslope flow over the Gallatin Valley is favorable for a at least a period of heavier snow, especially for the south and eastern portions of the valley. Given it's a weekday and the aforementioned portions of the valley currently have over 50% chance for 6 inches of snow, a winter storm watch was posted here. The most impactful period looks to occur late tonight through Thursday morning when precipitation will be heaviest and diurnal heating will be weakest. Impacts may include difficult travel due to slushy/snowy roads and reduced visibility, cold wet outback conditions, and even isolated power outages or tree damage. Snow begins to slowly diminish Thursday afternoon, but another shortwave looks to pass through and bring another round of light snow Thursday night into Friday. It's still uncertain on how widespread and impactful this will be, but the situation will continue to be monitored going forward. - RCG

AVIATION

15/18Z TAF Period

A cold front is moving through North-central, Central, and Southwestern Montana this afternoon and evening. This will change the wind direction at all terminals to more northerly and bring rain and snow to all TAF sites during this TAF Period. At the KBZN and KEKS terminals between 15/21Z and 16/06Z there is a a 15 - 20% chance for lightning. At the KWYS terminal between 16/03Z and 16/08Z there is a 15 - 20% chance for lightning. At the KHLN, KGTF, and KLWT terminals between 15/21Z and 16/03Z there is a 10 - 20% chance for lightning. During the duration of this TAF period at most of the terminals there is 30% chance or greater for rain, a rain/snow mix, or snow showers. During the majority of this TAF period there will be mountain obscuration across North-central, Central, and Southwestern Montana. Between 15/22Z and 16/06Z there will be isolated instances of mountain wave turbulence and low- level wind shear across Southwestern Montana. Across southwestern Montana this afternoon there is a low chance that a rain shower could mix down strong wind gusts in excess of 40kts. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 59 26 37 22 / 50 80 50 30 CTB 53 19 34 17 / 20 40 40 20 HLN 58 28 40 25 / 70 90 60 30 BZN 59 25 39 19 / 60 90 80 40 WYS 45 26 35 12 / 90 100 100 70 DLN 57 25 38 19 / 50 90 80 20 HVR 62 24 35 17 / 40 80 30 20 LWT 58 26 36 18 / 50 80 50 20

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until noon MDT Thursday for East Glacier Park Region.

Winter Weather Advisory from 6 PM this evening to noon MDT Thursday for Big Belt, Bridger and Castle Mountains-Little Belt and Highwood Mountains-Southern Rocky Mountain Front.

Winter Storm Watch from 6 PM MDT this evening through Thursday evening for Gallatin and Madison County Mountains and Centennial Mountains.

High Wind Warning until 9 PM MDT this evening for Beaverhead and Western Madison below 6000ft-Madison River Valley.

Winter Storm Watch from late tonight through Thursday afternoon for Gallatin Valley.

Winter Weather Advisory from 6 PM this evening to 6 AM MDT Thursday for Northwest Beaverhead County.