textproduct: Great Falls

KEY MESSAGES

- Cooler afternoon temperatures are expected across the area for the next few days.

- Showers and thunderstorms will become more widespread tonight into Thursday, few areas possibly getting over a half inch of rainfall.

- Lightning over the next few days could start new wildfires.

DISCUSSION

/Issued 425 AM MDT Wed Aug 12 2026/

- Meteorological Overview: The change to a cooler wetter weather pattern is beginning today. The flow aloft is becoming a bit more westerly today, as the upper level ridge breaks down. One disturbance is approaching the area from the north this morning, while another disturbance is approaching Southwest MT from the southwest. Overall expect shower and thunderstorm activity to start to increase late this morning through this afternoon. A few storms could produce strong wind gusts or heavy rainfall this afternoon/evening. The latest HREF does have one strong storm moving southeastward through North Central MT this evening, with the main impact being lightning/strong wind gusts. Otherwise, afternoon temperatures to start to cool a bit each day through Friday.

The chance for thunderstorms will increase Thu into Friday morning as precipitable water increases. Thus the chance for isolated flash flooding is possible from heavier showers. Additionally, a few storms could produce strong wind gusts on Thursday/Friday, especially over Southwest MT where it will be a bit more unstable.

The summertime upper level ridge of high pressure will try to rebuild over the northern Rockies starting this weekend. This will result in warmer, but more unstable air moving back into the CWA this weekend. Expect daily chances for showers/thunderstorms from Saturday through Tuesday. Again, the main concern from storms over the weekend will be lightning and strong wind gusts.

- Forecast Confidence & Scenarios: After a few days of cooler temperatures, warmer air moves back into the CWA this weekend. Thus afternoon temperatures could be a touch warmer than currently forecast, especially if some of the smoke clears out a bit.

The main concern from thunderstorms over the next few days will be lightning, brief heavy rainfall and strong wind gusts. Any lightning that occurs away from the main storm will be capable of producing new wildfires. Brusda

AVIATION

12/18Z TAF Period

VFR conditions will generally prevail throughout this TAF period, with the exception of periods of MVFR conditions due to passing thunderstorms. Thunderstorm activity in Southwest MT will begin around 22Z, moving northeast. Thunderstorm activity will also begin near KCTB around 23Z, moving east and southeast. Light rain will begin in North-Central/Central MT following the thunderstorm activity. Mountain obscuration is expected throughout this TAF period, as is a decrease in slant range visibility due to smoke from regional wildfires.

For KGTF: While small, there is a non-zero chance for cross winds in excess of 15 kts. However, sustained winds and wind gusts will be out of the northeast, with the exception of passing convection which could cause erratic winds. The latest HREF is continuing to show a thunderstorm in the Great Falls area around 13/02Z. Light rain is expected to follow this convective activity. -Dzomba

FIRE WEATHER

No fire weather statements will be issued at this time, but the main concern from today through this weekend will be lightning and thunderstorms that produce strong outflow wind gusts. Initially the thunderstorms will be on the wet side today through Friday, with drier thunderstorms possible over the weekend. Note any lightning that does occur away from the center of the storm will have a higher probability of starting a wildfire. Brusda

HYDROLOGY

A flash flood watch has been issued for the Horse Gulch burn scar area, which includes the Riverside Campground from this afternoon through the overnight hours. Several convective models have short/heavy producing rainfall storms moving over the burn scar this evening. Any one of these cells that move over the burn scar could produce flash flooding.

It is possible that additional flood statements might be needed for the Horse Gulch burn scar and the new burn scars in Beaverhead County for Thursday and Friday, as the shower/thunderstorm activity continues.

For other areas across the CWA, a marginal risk of flash flooding is possible from today through Friday from any storms that produce heavy rainfall. The overall probability is generally less than 15 percent of flash flooding, but precipitable water will increase over 1 inch by Thursday over the eastern portions of the CWA, allowing for that potential of flash flooding. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 78 52 70 50 / 0 80 80 70 CTB 65 46 60 44 / 50 80 100 70 HLN 81 53 73 53 / 10 60 40 80 BZN 87 50 77 49 / 10 40 40 80 WYS 79 40 72 39 / 50 40 60 80 DLN 84 49 76 48 / 10 20 70 70 HVR 77 48 69 47 / 20 90 90 60 LWT 78 49 68 47 / 20 90 80 80

TFX WATCHES/WARNINGS/ADVISORIES

Flash Flood Watch from 4 PM MDT this afternoon through late tonight for Big Belt, Bridger and Castle Mountains.