textproduct: Great Falls

KEY MESSAGES

- Showers and thunderstorms will affect the area this afternoon/evening and Tuesday 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 150 AM MDT Mon Aug 17 2026/

- Meteorological Overview:

Today there is an upper-level ridge with southwest flow aloft over North-central, Central, and Southwestern Montana. By this evening the upper-level ridge begins to break down and an upper- level trough begins to move over the area. This will bring breezy conditions to the area with isolated showers and thunderstorms this afternoon and evening. Temperatures will remain near seasonal averages on Monday. On Tuesday there will be zonal flow (west - east) over North-central, Central, and Southwestern. 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 on Tuesday.

On Wednesday and Thursday an upper-level ridge begins to build back in across North-central, Central, and Southwestern Montana. On Wednesday and Thursday temperatures will warm back up to around seasonal averages with dry weather. On Friday the upper-level ridge is over North-central, Central, and Southwestern Montana. This will bring hot and dry weather to the area. 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. -IG

- Forecast Confidence & Scenarios:

This morning in any areas that clear fog has a high chance to form. The areas that have the greatest risk for fog forming this morning are the valleys of Southwestern Montana.

Today the Storm Prediction Center (SPC) issued a Marginal Risk for Severe Thunderstorms (5% chance for wind gusts of 58 mph or greater within 25 miles of a point) for Judith Basin and Fergus Counties. Today there is a 15 - 25% chance for thunderstorms across North-central and Central Montana. Today there is a 20 - 35% chance for thunderstorms in Southwestern Montana. On Tuesday there is a 20 - 30% chance for thunderstorms across North-central, Central, and Southwestern Montana. Winds will increase and relative humidity will decrease Wednesday through Friday which will lead to elevated fire weather conditions. -IG

AVIATION

17/12Z TAF Period

VFR conditions will prevail at all terminals during this TAF Period outside of during any thunderstorms. After 17/18Z 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 all thunderstorms there will be a brief visibility reduction down to MVFR-levels and a brief period of mountain obscuration. -IG

For KGTF: Winds will be light and variable during this TAF period with a very low chance for exceeding the 15 kt crosswind threshold. Between 17/21Z and 18/03Z there is a 15% chance for a thunderstorm to affect KGTF. All thunderstorms will produce gusty, erratic winds which would exceed the 15 kt crosswind threshold. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 82 55 83 52 / 20 20 20 10 CTB 76 50 77 50 / 30 20 10 10 HLN 83 57 82 53 / 20 20 30 10 BZN 81 53 80 48 / 30 30 20 30 WYS 75 43 73 35 / 30 30 30 30 DLN 79 51 78 46 / 30 30 30 20 HVR 82 53 83 53 / 20 20 10 20 LWT 77 52 77 50 / 20 30 40 20

TFX WATCHES/WARNINGS/ADVISORIES

None.