textproduct: Great Falls

KEY MESSAGES

- Scattered showers and thunderstorms this evening will diminish by Midnight.

- Dry and warm conditions settle in Wednesday and Thursday.

- Breezy winds and showers and thunderstorms move in through the weekend.

UPDATE

Current forecast is on track, with no update planned for this evening. Showers/thunderstorms are diminishing from west to east this evening, with most of the showers exiting the eastern portions of the CWA by Midnight. Should be mostly dry across much of the area the next few days, with warmer afternoon temperatures ahead. Brusda

DISCUSSION

/Issued 546 PM MDT Tue Aug 18 2026/

- Meteorological Overview:

For the rest of today, a small shortwave trough moving through the region will continue to develop scattered showers and thunderstorms across the region. Weak instability of 500-1,000 j/kg and mid level moisture will help aid in thunderstorm development. One thing that is lacking is shear, with ~20kts of shear (closer to 30kts in Southwest MT) will limit longevity of storms. However, deep mixing and a dry surface layer creates a conducive environment for gusty to isolated severe wind gusts for mature/collapsing storms. DCAPE reaching near 1,000 j/kg supports this environment. Decent mid level lapse rates also supports a localized hail threat with the strongest storms.

After this shortwave trough passes, upper-level ridging builds in for Wednesday and Thursday. The lack of forcing will keep the region dry. Upper-level ridging continues into Friday with a trough building in along the West Coast U.S. Though, embedded vorticity maximums and an increase in monsoonal moisture returns showers and thunderstorm chances.

The trough propagates east over the weekend and into early next week, keeping showers and thunderstorms in the forecast. With the upper-level ridge breakdown comes an increase in mid level winds Saturday into Sunday and therefore surface winds. There remains some uncertainty in how strong the winds gets but there is good confidence for breezy winds for the weekend.

- Forecast Confidence & Scenarios:

There is some uncertainty in how strong the winds get this weekend. However there is better agreement in the timing of the winds (late Saturday through Sunday morning. Right now, there's a good coverage of 30-70% chances for 30 mph gusts Saturday and Sunday, with 20-40% chances for 40 mph winds along the Hi-line Sunday. Seems like the main limiting factor for fire weather is low confidence for critical relative humidities, but can't rule out elevated fire weather concerns if winds keep trending this weekend. Another thing to watch for this weekend is high PWAT values of an inch bringing a localized flash flooding threat to burn scars. -Wilson

AVIATION

19/00Z TAF Period

Scattered showers and thunderstorms are moving through Central MT and will end by 19/04Z. Primary threats remaining with the storms are brief strong gusts from outflows up to 45 KT, cloud-to-ground lightning, and localized heavy rain. Conditions will be VFR this evening into tomorrow morning for most terminals however there is a 40% chance for MVFR and 10% for IFR conditions at KWYS for fog/mist and ceilings from 19/09Z to 19/12Z.

For KGTF: VFR conditions will prevail with the passing of the thunderstorms. Winds will predominantly be out of the Southwest through the period from 8 to 12 KT on average however there is a small chance for brief variable wind shifts until 19/02Z due to residual outflow boundary interactions. - Akins

PRELIMINARY POINT TEMPS/POPS

GTF 54 86 55 85 / 10 0 0 0 CTB 52 82 52 78 / 20 10 0 0 HLN 52 86 53 89 / 30 0 0 0 BZN 49 83 50 90 / 0 0 0 0 WYS 37 79 39 84 / 30 0 0 0 DLN 48 83 49 86 / 0 0 0 0 HVR 55 87 55 87 / 0 0 0 0 LWT 52 82 52 85 / 20 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.