textproduct: Great Falls

KEY MESSAGES

- Scattered drier showers and thunderstorms develop across Southwest MT this afternoon and evening, with strong winds possible with storms.

- Better chances for showers and thunderstorms region wide Thursday, with isolated severe wind gusts possible.

- Breezy winds bring elevated fire weather conditions Thursday and Friday.

- Cooler temperatures, gusty winds, and precipitation continue this weekend and into the beginning of next week.

DISCUSSION

/Issued 234 PM MDT Wed Aug 26 2026/

- Meteorological Overview:

A shortwave rounding out the ridge axis today will develop scattered showers and thunderstorms across mainly Southwest and Central MT this afternoon and evening. Showers and thunderstorms are possible across North-Central MT this evening, but coverage and intensity look to be slightly less. Thunderstorms today will be on the drier side, with little precipitation reaching the ground. Strong mixing and a dry surface layer has resulted in DCAPE values approaching 1,000 j/kg. Strong gusty winds will be the primary hazard today. Thunderstorms have low confidence in becoming severe, but I can't rule out an isolated severe wind gust due to the strong mixing.

Increasing southwest flow due to the trough propagating east will advect in better shear and moisture Thursday for better coverage of showers and thunderstorms across the region. Steep lapse rates, stronger winds aloft mixing down, and modest shear will bring an isolated risk for severe wind gusts with thunderstorms. The increasing winds aloft will keep breezy synoptic winds across the region through the weekend until the trough passes through the region. Friday, the thunderstorm threat shifts southeast to the Dillon to Lewistown line. The breezy winds also bring elevated fire weather concerns Thursday and Friday.

The trough forms a closed low during the weekend which leads to better chances for scattered to widespread precipitation. There remains some uncertainty in the track of this low, which ultimately effects thunderstorm chances Saturday and Sunday. Recent runs have trended down on the chances of higher peak mountain snow Sunday morning, but I can't completely rule it out if the low track and cold air advection changes. Below normal temperatures will also limit severity of thunderstorms. Behind this wave, another trough forms along the West Coast U.S. However, difference in timing and amplitude leave details uncertain, but current forecast trends to cooler and some precipitation continuing.

- Forecast Confidence & Scenarios:

Models continue to show 30-50kts shear, steep lapse rates, and strong vertical mixing tomorrow to increase confidence in isolated severe thunderstorms to form. Severe wind gusts will be the main hazard, but with steep lapse rates and elevated CAPE focused in the hail growth zone, I can't rule out isolated large hail. PWATs between 0.70"-0.90" will bring a mix of wet and dry thunderstorms, with wet thunderstorms developing with the stronger storms.

Cooler temperatures this weekend tamper thunderstorm chances Saturday despite strong southwest flow from the incoming trough. The current closed low track has northwest cold air advection Sunday, which is not favorable for thunderstorms. However, a few runs shift the track a little south, keeping us in southwest flow with better chances for storms. -Wilson

AVIATION

27/00Z TAF Period

Scattered thunderstorms will continue to develop across the region with the main concerns being gusty/erratic winds and lightning. These thunderstorms are expected to last through the late evening across Southwest and Central Montana with impacts expected for most terminals. Mountain obscuration will remain a concern where thunderstorms are present. Additionally, smoke from nearby wildfires may impact slantwise visibility at times. Conditions will calm down overnight with another round of widespread showers and thunderstorms expected Thursday afternoon.

For KGTF: As of 26/2345Z, thunderstorms are currently developing and moving into Cascade county and will continue to head due east over the next couple hours. Additional showers are also trying to develop along the western portion of the county and may fill in the line of thunderstorms as it approaches KGTF. The timeframe of greatest concern is between now and 27/02Z although some lingering thunderstorm and gusty winds could last as late as 07/04Z depending on how quickly these storms move through. During this time gusts up to 40kts are possible with frequent lightning in the vicinity of stronger storms.

Beyond 07/04Z, winds will be light and variable through the overnight hours with the next chance for thunderstorms and gusty winds expected Thursday after 27/19Z. -thor

FIRE WEATHER

Very warm, dry, and breezy conditions will combine with thunderstorm activity for elevated fire weather conditions for the next couple of days, especially for southwest and portions of central Montana. The primary concern will be passing waves of showers and thunderstorms, some with little rainfall and cloud to ground lightning. The strongest storms may produce erratic gusty winds over 50 mph,which may help spread new fires. Thursday and Friday look to be the breeziest and driest days for central and southwestern locations north of I90, with up to a 20% chance for the Hot Dry Windy Index to exceed the 90th percentile. Fire weather products are not planned to be sent out at this time given the marginal conditions, but the situation will continue to be monitored. A Pacific trough brings additional showers and thunderstorms and periods of gusty winds this weekend; however, cooler temperatures and more productive storms looks to reduce the fire risk. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 59 94 57 86 / 20 30 40 0 CTB 54 88 54 81 / 10 20 10 0 HLN 55 90 54 83 / 40 50 40 10 BZN 54 89 53 81 / 20 30 40 40 WYS 42 82 43 72 / 40 20 30 70 DLN 52 86 52 79 / 20 40 20 40 HVR 61 98 60 90 / 0 20 40 0 LWT 57 93 56 84 / 20 50 30 20

TFX WATCHES/WARNINGS/ADVISORIES

None.