textproduct: Great Falls

KEY MESSAGES

- Above average warmth through Friday.

- Scattered showers and isolated thunderstorms primarily across southwest MT this evening and overnight.

- Pacific weather system brings windy and cooler conditions for the upcoming weekend.

DISCUSSION

/Issued 206 AM MDT Tue Sep 22 2026/

- Meteorological Overview:

Large scale ridging centered east of the region will maintain above average warmth and a southwesterly flow aloft across the Northern Rockies and MT through Friday before a broadening upper trough in the North Pacific edges inland this weekend. An upper level disturbance and some monsoon-related moisture embedded within the southwesterly flow around the ridge will spread increasing cloud- cover northward across the area today with scattered showers and isolated weak thunderstorms tracking across primarily SW MT late this afternoon through tonight. The warmest temperatures this week are likely Thursday and Friday as southwesterly flow increases ahead of the incoming upper trough with afternoon temperatures pushing well into the 80s for many areas. This would be around 15 degrees above seasonal averages but well below daily records, which are still in the lower to mid 90s.

A relatively strong Pacific cold front is forecast to traverse the northern Rockies late Friday into Friday night. However, model discrepancies persist regarding the precise timing and intensity of the embedded shortwave as it lifts northeastward from the Northern Rockies into AB by Saturday morning. Gusty southwest winds are likely to precede the front late Friday with showers and potentially some thunderstorms accompanying the frontal passage, followed by gusty west winds and cooler temperatures for the weekend.

- Forecast Confidence & Scenarios:

Instability will be constrained this afternoon due to high cloud- cover and decreasing late September solar input, keeping CAPE values mostly under 500 J/kg. Consequently, thunderstorm threats will be limited primarily to isolated lighting strikes and wind gusts to around 30 mph.

The main hazard to watch with the approaching Pacific trough and cold front early this weekend remains the potential for elevated winds Friday night into Saturday. Recent model guidance has shifted the shortwave slightly further north however, and somewhat weakened the accompanying mid-level wind field. The overall setup, featuring downward transport of winds following the shortwave and moderate pressure rises in the wake of the front, continues to support the potential for locally strong winds gusts and probabilistic guidance now indicates a 30-40% chance of gusts exceeding 55 mph along the Rocky Mountain Front and adjacent areas on Saturday. Hoenisch

AVIATION

22/12Z TAF Period.

Fog development early this morning is mainly limited to areas near the Milk River and upper Missouri breaks, but will include the KHVR vicinity, where LIFR cigs/vis are possible through 16z. Elsewhere, VFR conditions prevail with an increase in mid to high level cloud-cover from south to north through this afternoon. Scattered showers and a few isolated/weak thunderstorms develop across southwest MT late this afternoon and look to track as far north as near KHLN and KLWT overnight. Some local mountain obscuration and brief MVFR conditions are possible near showers this evening/overnight. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 80 52 80 49 / 0 0 0 0 CTB 77 48 73 45 / 0 0 0 0 HLN 77 49 77 48 / 10 20 0 0 BZN 75 47 75 45 / 0 30 0 0 WYS 66 35 64 30 / 0 60 0 0 DLN 73 43 74 42 / 10 40 0 0 HVR 80 50 81 47 / 0 0 10 0 LWT 79 50 77 48 / 0 20 20 0

TFX WATCHES/WARNINGS/ADVISORIES

None.