textproduct: Great Falls

KEY MESSAGES

- Marginal risk for severe thunderstorms over the plains of Central and North Central Montana Wednesday, with the primary risk being damaging winds.

- Above normal temperatures today falling near to below normal for the remainder of the week.

- Strong and gusty winds on Wednesday and Thursday, especially within the north-south orientated valleys of Southwest Montana.

DISCUSSION

/Issued 843 AM MDT Tue Sep 1 2026/

- Meteorological Overview:

Longwave troughing over the Western CONUS, with south to southwest flow aloft across the Northern Rockies, will dominate the upcoming week. Shortwaves ejecting from the base of the trough axis and lifting north to northeast within the aforementioned flow regime will bring multiple opportunities for showers and thunderstorms to Southwest through North Central Montana, most notably today and Wednesday when the areal coverage precipitation will be greatest. High temperatures, with the exception of today when highs will generally be 5 to 10 degrees above normal, will mostly range from near to below normal. Periods of strong and gusty winds will occur over the next week, especially on Wednesday and Thursday within the north-south orientated valleys of Southwest Montana where frequent gusts in excess of 45 mph are likely to occur. - Moldan

- Forecast Confidence & Scenarios:

Strong Winds on Wednesday and Thursday...

ECMWF EFIs with respect to winds continue to support the potential for an unusual to very unusual wind event, for early September, through the period along and south of the I-90 corridor; most notably within the Madison River Valley. Southerly H700 winds per NAEFS analysis across Southwest Montana are prog'd to increase to between 30-40kts by 18z Wednesday, and remain so through 00z Friday before decreasing. These 2 to 2.5 standard deviation wind speeds aligned with the north-south terrain in Southwest Montana, specifically the Madison River Valley, combined with deep mixing between 16z to 02z each day will support an ideal scenario for an early season High Wind event. Given that NBM5.0 probabilities within the Madison River for sustained wind speeds to exceed 40 mph range between a 60-70% chance (Wednesday) and 30-40% chance (Thursday), confidence remains high enough to continue the High Wind Watch with this forecast package. The main reason for not upgrading the High Wind Watch was uncertainty with respect to Wednesday night's into Thursday's winds, which at this point in time appear to be slightly weaker than during the daylight hours on Wednesday. Additionally, I was unable to find a (6-9 hour) period in which wind speeds and/or gusts decrease significantly enough in order to break-up the event into two (2) distinct wind events, thus the watch from 18z Wednesday through 03z Friday remains in effect for the Madison River Valley.

Listed below are the NBM5.0 probabilities for wind gusts to exceed 35, 45, and 55 mph for select locations across North Central, Central, and Southwest Montana.

Wednesday's Wind Gusts Probabilities LOCATION > 35 mph | > 45 mph | > 55 mph Browning 95% | 50% | 5% Cut Bank 95% | 60% | 15% Havre 80% | 40% | 5% Great Falls 90% | 60% | 20% Lewistown 60% | 10% | <5% Helena 80% | 45% | 15% Bozeman 90% | 65% | 15% Dillon 90% | 70% | 25% Ennis 100% | 85% | 30% West Yellowstone 95% | 60% | 0%

Thursday's Wind Gusts Probabilities LOCATION > 35 mph | > 45 mph | > 55 mph Browning 90% | 65% | 20% Cut Bank 90% | 65% | 20% Havre 75% | 35% | <5% Great Falls 80% | 45% | 5% Lewistown 70% | 5% | 0% Helena 75% | 25% | 0% Bozeman 85% | 50% | 5% Dillon 100% | 60% | 10% Ennis 95% | 70% | 5% West Yellowstone 85% | 40% | 0%

Severe Thunderstorm Risk for Wednesday...

A marginal risk for severe thunderstorms, mainly capable of producing damaging winds, exists on Wednesday along and northwest of a Helena, to Monarch, to Winifred line. Showers and thunderstorms lifting northeast from Idaho and Western Montana are expected to overspread the aforementioned area through the afternoon hours, with BUFKIT sounding depicting inverted-V's beneath cloud bases of 10000kft. These high cloud bases combined with already anomalous low level wind speeds will support the potential for a few severe thunderstorm/shower wind gusts across portions of Central and North Central Montana. - Moldan

AVIATION

01/18Z TAF Period

VFR conditions will prevail at all terminals during this TAF Period outside of during any thunderstorms. Showers and thunderstorms will affect the KBZN, KEKS, KWYS, and KHLN terminals between 02/01Z and 02/10Z. During any thunderstorms there will be gusty, erratic winds, lightning, and a brief heavy downpour. The heavy downpour could briefly cause mountain obscuration and a reduction in visibility to MVFR-levels. Winds will between to increase across Southwestern Montana by the end of this TAF Period. During this TAF Period smoke from wildfires will reduce slantwise visibility across all terminals. -IG

For KGTF: Winds will be light through at least 00Z with a zero percent chance for exceeding the 15kt crosswind threshold. Between 01Z and 05Z there is a 30% chance for wind gusts to exceed the 15 kt crosswind threshold. Between 05Z and 08Z there is a 20 - 30% chance for a shower and/or thunderstorm to reach KGTF and produce an outflow wind which would exceed the 15kt crosswind threshold. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 85 56 81 48 / 0 10 50 20 CTB 83 52 77 45 / 0 10 70 50 HLN 86 51 78 48 / 10 40 60 10 BZN 82 49 77 45 / 20 40 20 0 WYS 69 37 64 33 / 40 60 20 0 DLN 81 45 74 42 / 30 50 60 10 HVR 88 54 87 49 / 0 0 50 60 LWT 83 54 82 48 / 10 10 30 10

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Watch from Wednesday afternoon through Thursday evening for Madison River Valley.