textproduct: Great Falls

KEY MESSAGES

- Areas of rain near the Canadian border late today into tonight.

- Dry conditions Wednesday ahead of showers/thunderstorms Thursday afternoon through Friday night.

- Warmer and drier conditions by the end of the weekend.

UPDATE

/Issued 734 PM MDT Tue Sep 15 2026/

The main changes to the forecast was to increase coverage of PoPs across North-Central MT. Current radar shows light isolated showers initiating due to a small boundary. Light rain is expected to continue across parts of North-Central MT through early Wednesday morning, but coverage of rain greatly drops off around midnight. There is a low end chance for patchy fog Wednesday morning, but lower clouds may prohibit development. -Wilson

DISCUSSION

/Issued 734 PM MDT Tue Sep 15 2026/

- Meteorological Overview:

Due to an upper-level trough clipping north MT, there will be areas of light rain showers this evening through the early hours of Wednesday morning. However, showers are expected to be limited to north central MT and the north Rockies.

Wednesday will be a break between the two upper level troughs as weak upper level ridging will be present. As such, conditions will be dry and mild for the majority of the state.

During Tuesday night and Wednesday, the trough that has been sitting stagnant over the PNW will develop a closed off low and begin shifting eastward. This eastward movement will cause upper level SW flow to develop over MT on Wednesday. The upper level SW flow is expected to continue through Saturday as the upper level low continues its eastward track across the state.

Although upper level SW flow is expected to develop Wednesday, warmer weather and the potential for showers/thunderstorms are expected to hold off until Thursday. Looking at Thursday and beyond, warmer weather and the potential for showers/thunderstorms will continue through Friday night. By midday Saturday, the potential for showers/thunderstorms will have ended as the low makes continues its eastward track across the state.

Beginning Sunday, a period of warmer and drier conditions will develop and is expected to continue into the beginning of the following week. - ESH

- Forecast Confidence & Scenarios:

Thunderstorms on Thursday and Friday...

CAPE and shear per ECMWF EFIs will climb to between 0.6 and 0.75 along and south of the I-90 corridor on both Thursday and Friday, with Friday having the greatest coverage of EFIs in excess of 0.6 across the aforementioned region. BUFKIT soundings across Southwest Montana indicate high cloud bases in excess of 10kft, with very dry air beneath these bases (i.e. inverted-Vs). This dry air combined with climatologically unusual, with respect to September climatology), instability and shear would lend to the idea that a few thunderstorms that develop on either day would be capable of producing strong and erratic outflow winds. BUFKIT soundings also indicate tall and skinny CAPE profiles across Southwest and portions of Central Montana, which when considered against PWATs of 2-3 standard deviations above normal (or between 0.75" to 1") suggests the potential for some thunderstorms to produce heavy rainfall. - Moldan

AVIATION

16/06Z TAF Period

Initial concern will be for areas of rain and low clouds, mainly across the plains through the morning. Ceilings slowly rise and scatter out through the day Wednesday as daytime mixing ensues. A few instances of low-level wind shear will be around Wednesday evening as easterly low level flow ensues near sunset. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 43 62 42 72 / 20 0 0 0 CTB 43 58 39 68 / 70 20 0 0 HLN 44 67 44 78 / 10 0 0 0 BZN 38 71 40 77 / 0 0 0 20 WYS 28 74 37 71 / 0 0 30 70 DLN 37 72 42 77 / 10 0 10 30 HVR 44 65 42 75 / 50 10 0 0 LWT 40 64 42 76 / 20 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.