textproduct: Great Falls

KEY MESSAGES

- Flash Flood Watch remains in effect for the Pioneer Mountains through this evening.

- Temperatures moderate through the weekend and early next week, but remain below to near normal.

- Shower and thunderstorms chances will persist through the middle of the upcoming work week, most notably through tonight and then again Monday afternoon through Tuesday afternoon.

DISCUSSION

/Issued 1257 PM MDT Fri Aug 14 2026/

- Meteorological Overview:

Moist, southwest flow aloft and overall north-to-east low level flow will help to maintain precipitation chances and below-to-near normal temperatures through the middle of the upcoming work. Over this stretch Sunday and Monday will be the closest to normal, with respect to high temperatures, as surface winds briefly become southwesterly and supporting some "warming" as compared to the Saturday, Tuesday, and Wednesday. Monsoonal moisture lifting north and east within the southwest flow aloft will maintain daily chances for showers and thunderstorms, most notably from Monday afternoon/evening through the Tuesday afternoon. While thunderstorms from this weekend through the middle of the work week will generally be of the garden variety a few stronger storms producing strong wind gusts can't be ruled out as low level moisture gradually erodes leading to inverted-V soundings, especially across Southwest Montana. - Moldan

- Forecast Confidence & Scenarios:

Flooding risk through this evening:

12z Hi-Res Ensemble Forecast (HREF) guidance supports a 20-30% chance that hourly rainfall rates could exceed 0.25"/hr from the late afternoon through evening hours tonight over the burn scars across the Pioneer Mountains, with these probabilities appearing reasonable given morning observations of between 0.1"-0.3" across Southwest through North Central Montana. Given that the threshold for flash flooding is so low over the active fires in the Pioneers, and that they have already received a wetting rain over the previous 24 hours, a Flash Flood Watch remains in effect through 9 pm this evening.

Concerns for flash flooding on the the Horse Gulch Burn Scar remain lower than that of the Pioneer Mountain Burn Scars given a lower probability for hourly rainfall rates to exceed 0.5"/hr here, with these probabilities being around a 10% chance. While flash flooding can not be ruled across the Horse Gulch Burn Scar through the evening hours tonight confidence in any flooding remains too low to issue a Flash Food Watch. -Moldan/AM

AVIATION

15/00Z TAF Period

Initial concern this TAF period will be for scattered showers and thunderstorms over Southwest and Central Montana, in addition to rain and low clouds over the plains. The shower and thunderstorm activity wanes later this evening, while the low clouds over the plains persist into tonight and early Saturday. While lower probability, I cannot quite rule out some fog tonight in areas that see ample precipitation and end up clearing out.

Gradual improvement to ceilings is forecast Saturday morning and early afternoon over the plains as daytime mixing ensues. Another round of showers and thunderstorms looks to develop across Southwest Montana by the early afternoon Saturday with gusty winds being the primary concern.

For KGTF: Low clouds in the area will hold on through the overnight and through the morning. This cloud layer looks to fall in a layer warmer than 0C through the remainder of the event, which will keep icing concerns lower. Daytime mixing looks to break up the lower clouds early afternoon Saturday. Winds over the next 24 hours look light, yielding a very low risk for any cross-wind concerns. -AM

HYDROLOGY

A Flash Flood Watch remains in effect for the Bobcat Lakes and Sand Creek Burn Scars in the Pioneer Mountains through the evening hours tonight. Given the intensity of burning that occurred through much of the past week soils are likely to be hydrophobic, which combined with the steep and complex terrain of the Pioneer could lead to flash flooding and debris flows. - Moldan

PRELIMINARY POINT TEMPS/POPS

GTF 51 77 51 84 / 50 10 10 10 CTB 44 73 46 78 / 20 10 10 10 HLN 50 77 51 82 / 40 30 30 10 BZN 46 76 46 79 / 60 30 50 0 WYS 34 71 34 74 / 70 40 60 10 DLN 46 73 45 77 / 40 70 50 10 HVR 49 77 49 85 / 50 10 20 0 LWT 49 72 50 78 / 60 30 50 20

TFX WATCHES/WARNINGS/ADVISORIES

Flash Flood Watch until 9 PM MDT this evening for Northwest Beaverhead County.