textproduct: Great Falls

KEY MESSAGES

- Showers and thunderstorms will affect the area this afternoon/evening.

- Temperatures will be around seasonal averages throughout this week.

- It will be dry Wednesday through Friday with thunderstorms returning this weekend with breezy conditions.

DISCUSSION

/Issued 136 AM MDT Tue Aug 18 2026/

- Meteorological Overview:

Today there will be zonal flow (west - east) over North-central, Central, and Southwestern Montana. This will allow temperatures to remain near seasonal averages with breezy conditions due to modestly strong low and mid-level winds. There will also be showers and thunderstorms across North-central, Central, and Southwestern Montana this afternoon/evening. On Wednesday an upper-level ridge begins to build back in across North-central, Central, and Southwestern Montana. On Wednesday temperatures will be around seasonal averages with dry weather. On Thursday the upper-level ridge remains over North-central, Central, and Southwestern Montana. This will keep warm and dry conditions for the area on Thursday. On Wednesday and Thursday upper-level shortwaves will move through the upper-level flow and bring breezy conditions to North-central, Central, and Southwestern Montana.

On Friday the upper-level ridge remains over North-central, Central, and Southwestern Montana. This will bring hot and dry weather to the area. An upper-level shortwave will move through the upper-level flow and bring breezy conditions to North- central, Central, and Southwestern Montana. On Saturday an upper- level trough begins to move over North-central, Central, and Southwestern Montana. This will bring showers and thunderstorms back to the area. Due to modestly strong low-level and mid-level winds it will be breezy on Saturday. On Sunday the upper-level trough is over North-central, Central, and Southwestern Montana. This will cool down temperatures slightly and bring another round of showers and thunderstorms to the area. On Sunday due to modestly strong low and mid-level winds it will be breezy across North-central, Central, and Southwestern Montana. On Monday an upper-level ridge moves over North-central, Central, and Southwestern Montana. This will bring warm and mostly dry weather to the area on Monday. -IG

- Forecast Confidence & Scenarios:

Today the Storm Prediction Center (SPC) issued a Marginal Risk (5% chance for wind gusts of 58 mph or greater within 25 miles of a point) for Choteau, Judith Basin, Fergus, and Southern Blaine Counties. Today there is a 20 - 35% chance for thunderstorms across North-central, Central, and Southwestern Montana.

Winds will increase and relative humidity will decrease Wednesday through Sunday which will lead to elevated fire weather conditions. Saturday evening through Sunday is the time period when the winds increase the most and so Sunday afternoon currently has the greatest risk for near critical fire weather conditions. This risk is contingent on the track of the upper-level trough that moves through Saturday evening into Sunday. -IG

AVIATION

18/12Z TAF Period

VFR conditions will prevail at terminals during this TAF Period outside of during any thunderstorms. After 18/18Z showers and thunderstorms will be around all terminals. At this time there is low confidence in thunderstorms affecting any of the terminals. All thunderstorms will produce frequent lightning, a brief heavy downpour, and gusty, erratic winds with the strongest thunderstorms producing strong wind gusts. The greatest threat for the strongest thunderstorms is at the KLWT terminal. During any thunderstorms there will a brief visibility reduction down to MVFR-levels and a brief period of mountain obscuration. During this TAF Period smoke from wildfires will reduce slantwise visibility at the KCTB and KHVR terminals. -IG

For KGTF: Winds will be light and variable until about 21Z when they will increase to about 12 kt with gusts up to 16 kt and be westerly. Between 21Z and 03Z there is a 50% chance for exceeding a 15 kt crosswind. Winds will then become light and variable after 03Z. Between 21Z and 00Z there is a 15% chance for a thunderstorm. The primary risks from any thunderstorms are gusty winds exceeding the 15 kt crosswind threshold and frequent lightning. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 83 54 86 55 / 20 20 0 0 CTB 78 52 82 52 / 20 20 0 0 HLN 83 52 86 53 / 30 30 0 0 BZN 79 49 83 50 / 30 30 0 0 WYS 75 37 79 39 / 30 30 0 0 DLN 79 48 83 49 / 30 20 0 0 HVR 85 55 87 55 / 20 20 0 0 LWT 79 52 82 52 / 30 20 0 0

TFX WATCHES/WARNINGS/ADVISORIES

None.