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.

DISCUSSION

/Issued 344 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

07/12Z TAF Period

RA with embedded TSRA will continue to bring a mix of IFR to MVFR conditions across North Central Montana airports (KCTB, KHVR, KGTF, KLWT) through the daylight hours today due to a mix of lower visibility and ceilings. Further south, watch for SHRA with embedded TSRA to continue through at least the morning hours before some clearing arrives late this morning/after 18z. RA will persist across the plains beyond 12z tomorrow across the plains before conditions improve there as well.

For KGTF: Expect generally MVFR conditions through the day today with periods of IFR conditions through the day during heavier rain and thunderstorms. Winds will be on the increase today, and while winds through 19z or so will be aligned enough with the runway to keep crosswinds under 15 kts, a shift further to the west is expected by 21z as winds increase further, resulting in a near certainty of crosswinds approaching 20 to 25kts. Ludwig

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 90 10 HLN 65 43 68 44 / 100 20 10 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 90 100 50 LWT 67 43 64 41 / 90 20 30 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.