textproduct: Great Falls

KEY MESSAGES

- Moderate to heavy rain will continue to affect mainly North Central Montana through Tuesday morning.

- Warmer and drier conditions arrive for Wednesday and Thursday.

- Another cooler wetter period is expected for Friday and into the weekend.

UPDATE

/Issued 855 AM MDT Mon Sep 7 2026/ Updated forecast is out for this morning, with pops mostly freshened for the rest of this morning. A band of rain continues to push northward this morning through North Central MT. Rainfall around a half inch is common with this band. Other isolated thunderstorms are developing west of Bozeman currently. The focus for rain/thunderstorms will shift to the Highway 2 corridor from Browning to Harlem this afternoon. Brusda

DISCUSSION

/Issued 855 AM MDT Mon Sep 7 2026/

- Meteorological Overview:

Deep and slow moving upper level low pressure will continue to slowly drift eastward over the Treasure State over the next 36-48 hours, bringing a prolonged period of cool and wet weather. Overnight showers and thunderstorms that moved through the area will gradually coalesce across North Central Montana and along the Rocky Mountain Front, where they will more or less persist through the day today and into early Tuesday.

A brief period of respite from the wet weather will arrive Wednesday and Thursday as weak upper level ridging transits the area. As the ridge moves overhead, temperatures will be a bit closer to average, with highs generally in the 70s to low 80s across the lower elevations. This warmer and drier period will not last long, however, as our next upper level low will push in Friday and Saturday, bringing another prolonged period of cooler and wetter weather.

- Forecast Confidence & Scenarios:

Rain through Tuesday: Models remain in overall good agreement that the heaviest rainfall will generally remain confined to the Rocky Mountain Front and along the Hi-Line, where amounts of 1.5 to 3 inches of additional rainfall remain possible. Areas that received heavy rainfall from the strong to severe thunderstorms that rolled through the area Sunday night will need to be watched extra closely, as this extra moisture may provide the antecedent conditions needed for the rainfall to over saturate some of the soils locally and result in some localized flooding. Ludwig

AVIATION

07/18Z TAF Period

A rain band/shield will continue along the Rocky Mountain Front and US Highway 2 through Tuesday morning. There might be a few showers/thunderstorms embedded in this line of rain this afternoon. Periodic moderate bands of rain will also be possible. West/southwest winds are expected to increase across the region this afternoon, with breezy to gusty winds lasting until early Tuesday morning.

For KGTF: Isolated showers and thunderstorms will pop up near the terminal early this afternoon. With winds turning a bit more westerly during the afternoon at 20 to 30kts, there is high confidence in exceeding crosswind thresholds through early Tuesday morning. There remains some uncertainty on if the rain shield later tonight shifts down to the terminal or just stay to the north. -Wilson

HYDROLOGY

While areas along the Rocky Mountain Front have received 0.75" to 1.5" of rainfall over the past day or two, there hasn't been much of a response in creeks/streams yet due to the drier grounding soaking all the rain up. The main concern is another additional widespread 1 to 3 inches and isolated 4 inches through Tuesday morning on a more saturated ground. Areas that get the higher end 3 to 4 inch totals may see minor overflow in creeks/streams along with muddied rural roads. The wet conditions can also cause rock/debris slides in the higher terrain. Therefore, a flood watch was issued through Tuesday. Farther east across North-Central MT will see wetting rain, but confidence for those higher end totals remain low. Two things to watch for is any eastern shift of these amounts farther east along US Highway 2 towards Hill County, and any heavier showers that affect areas that saw heavy rain Sunday night could see some increased risk for minor flooding. -Wilson/Ludwig

PRELIMINARY POINT TEMPS/POPS

GTF 63 46 64 43 / 100 40 70 10 CTB 56 43 60 43 / 100 90 70 0 HLN 65 43 68 44 / 100 0 20 0 BZN 67 39 70 39 / 90 0 0 0 WYS 60 30 63 30 / 30 0 0 0 DLN 66 36 70 37 / 40 0 0 0 HVR 67 46 63 43 / 100 90 90 40 LWT 67 43 64 41 / 90 10 40 20

TFX WATCHES/WARNINGS/ADVISORIES

Flood Watch through Tuesday morning for East Glacier Park Region- Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Northern High Plains-Southern High Plains-Southern Rocky Mountain Front.