textproduct: Great Falls

KEY MESSAGES

- Another cooler day with showers and thunderstorms.

- Some thunderstorms will be capable of heavy rain today.

- Trending warmer this weekend, though afternoon and evening showers and thunderstorms will remain.

DISCUSSION

/Issued 1239 AM MDT Fri Aug 14 2026/

- Meteorological Overview:

A southwesterly flow aloft will persist across the region over the upcoming week. This flow aloft is initially cyclonic in nature, which will aid in lots of showers and thunderstorms, even during the overnight, through tonight. Precipitable water values are still somewhat elevated, which will allow for a few stronger thunderstorms to produce heavy rainfall rates, at least briefly. Should one of these stronger thunderstorms move over an urban area or a burn scar, there would be flash flooding concerns.

Heading into the weekend the southwesterly flow becomes more anticyclonic in nature, with rising heights aloft. Typically this would suppress convection somewhat, but given the forecast lingering moisture near the surface across Southwest and Central Montana and rising temperatures, another round of showers and thunderstorms looks to develop Saturday afternoon and evening. Precipitable water looks to decrease at least somewhat, which would favor a lower probability for excessive rainfall.

The same story plays out Sunday, though with another day of drying, overall coverage of showers and thunderstorms becomes more questionable. Continued southwest flow aloft with a few embedded waves will foster additional round of scattered showers and thunderstorms into early next week as temperatures trend to near average. Confidence in specifics wanes after Tuesday, though the main takeaway continues to be for additional scattered showers and thunderstorms. -AM

- Forecast Confidence & Scenarios:

Flooding risk today:

Precipitable water values fall ever so slightly today, but still look to be high enough to result in some heavier rainfall rates. Storm motions look to be slightly faster, which also would favor lesser of a risk for excessive rainfall leading to flash flooding. Given 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, another flash flood watch was issued from 1 pm to 9 pm for today. A few high resolution members take a shower or thunderstorm through this area early this morning, but the probability of this occurring is too low to warrant having the watch begin early this morning. Trends will continue to be monitored for changes in confidence in this area this morning.

As of now the concern level at Horse Gulch Burn Scar is slightly lower. Should this concern level rise even slightly, an additional flash flood watch would become necessary. -AM

AVIATION

14/12Z TAF Period

VFR conditions will prevail across the KEKS and KWYS terminals during this TAF Period. During this TAF Period at the KBZN, KGTF, KCTB, and KLWT terminals ceilings will lower to at least IFR-levels. During this TAF Period there will be showers and thunderstorms across North-central, Central, and Southwestern Montana. During the duration of this TAF Period there will be mountain obscuration across North-central, Central, and Southwestern Montana. -IG

For KGTF: Light winds are forecast this TAF period, which will yield a nearly zero probability of a 15 kt crosswind. Aside from the low clouds and intermittent showers or isolated thunderstorm, the main concern will be for icing. Most forecast soundings feature at least at shallow layer of clouds in the 0C to -15C range through the early afternoon today. -IG/AM

HYDROLOGY

Precipitable water values fall ever so slightly Friday, but still look to be high enough to result in some heavier rainfall rates. Storm motions look to be slightly faster, which also would favor lesser of a risk for excessive rainfall leading to flash flooding. Given 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, another flash flood watch was issued from 1 pm to 9 pm for today. HREF probabilities for a quarter inch of rain over an hour in the neighborhood of the active fires is roughly 50%. This gave enough confidence to warrant the flash flood watch. Trends will continue to be monitored further north for the Horse Gulch Burn Scar for an additional flash flood watch.

PRELIMINARY POINT TEMPS/POPS

GTF 66 50 76 50 / 60 40 0 20 CTB 59 44 71 45 / 50 20 0 10 HLN 70 50 77 51 / 60 50 20 40 BZN 73 47 75 46 / 60 60 30 40 WYS 66 35 70 34 / 60 60 60 60 DLN 72 45 73 44 / 70 50 50 50 HVR 68 48 76 48 / 50 30 10 20 LWT 65 47 72 48 / 70 40 40 40

TFX WATCHES/WARNINGS/ADVISORIES

Flash Flood Watch from 1 PM MDT this afternoon through this evening for Northwest Beaverhead County.