textproduct: Great Falls

KEY MESSAGES

- Showers and thunderstorms are expected each afternoon through Saturday.

- Isolated thunderstorms in Southwestern Montana have the potential to produce localized flash flooding this afternoon/evening.

- Temperatures will gradually warm up through Saturday and stay warm through early next week.

DISCUSSION

/Issued 214 PM MDT Wed Jul 22 2026/

- Meteorological Overview:

This afternoon there is an upper-level ridge over North-central, Central, and Southwestern Montana. An upper-level shortwave will move through the upper-level flow and bring shower and thunderstorms primarily south of I-90 Wednesday afternoon and evening. Due to an increase in monsoonal moisture the thunderstorms will produce heavy rainfall. There is a lack of steering flow so the thunderstorms will also be slow moving. This has the potential to lead to some localized flooding. See the Hydrology section for details. On Wednesday isolated and showers have the potential to make it further north but stay south of an Augusta to Great Falls to Lewistown line.

On Thursday the upper-level ridge remains over North-central, Central, and Southwestern Montana. Another upper-level shortwave moves through the flow. This will bring another day of hot weather with isolated showers and thunderstorms. On Friday the upper-level ridge remains over North-central, Central, and Southwestern Montana. This will increase temperatures to well-above seasonal averages. Winds will increase due to low-level and mid-level winds increasing. This will dry out the area and bring elevated fire weather conditions to North-central Montana. See the Fire Weather Section for details. On Saturday the upper-level ridge remains over North- central, Central, and Southwestern Montana. It will be the hottest out of this forecast period across the area on Saturday with well- above seasonal average temperatures. On Sunday a weak upper-level trough moves through which will slightly cool down temperatures and bring some windy conditions to the area. On Monday and Tuesday the upper-level ridge remains over North-central, Central, and Southwestern Montana. This will allow warm and dry conditions to persist. -IG

- Forecast Confidence & Scenarios:

On Wednesday there is a 40 - 60% chance for thunderstorms across Southwestern Montana. On Wednesday there is a 15 - 35% chance for thunderstorms across most of North-central and Central Montana. On Thursday there is a 20 - 40% chance for thunderstorms across North- central, Central, and Southwestern Montana. On Friday there is a 25 - 30% chance for thunderstorms across Southwestern Montana. On Saturday there is a 25 - 50% chance for thunderstorms across Southwestern Montana.

On Friday there is a 20 - 60% chance for high temperatures of 100 degrees or greater across most of North-central Montana. On Saturday there is greater than a 60% chance for high temperatures of 100 degrees or greater across North-central Montana. On Saturday across portions of Fergus, Hill, and Blaine Counties there is a greater than a 70% chance for high temperatures greater than 105 degrees. This combined with low temperatures in the upper 60s to low 70s across portions of Fergus, Hill, and Blaine County on Saturday and Sunday morning led to an Excessive Heat Watch being issued for those areas from Friday afternoon through Sunday evening. On Saturday there is a 40 - 60% chance for high temperatures of 100 degrees or greater from the Helena Valley through the Canyon Ferry area to Townsend to the Three Forks to Bozeman area. -IG

AVIATION

23/00Z TAF Period

VFR conditions will prevail across all terminals during this TAF Period outside of during any thunderstorms. At the beginning and end of this TAF Period there is a 20 - 40% chance for thunderstorms at the KEKS, KBZN, KHLN, and KWYS terminals. At the end of this TAF Period there is a 20% chance for thunderstorms at the KLWT terminal. Any thunderstorms will produce heavy rainfall, small hail, frequent lightning, and gusty, erratic winds. During any thunderstorms there will be a brief period of mountain obscuration. Across most of the TAF sites smoke from wildfires will reduce slantwise visibility. -IG

FIRE WEATHER

Hot, dry, and windy conditions are expected through the weekend which will lead to elevated fire weather concerns across much of the region. The main limiting factor will be the potential for wetter showers and thunderstorms both this afternoon/evening and Thursday.

There is a concern that most of the wetter showers will not make it north of a line between Helena and White Sulphur Springs which would put North-Central Montana at a much higher risk for elevated fire weather conditions through the weekend. Additionally, if the wetter storms on Wednesday and Thursday are unable to materialize, or they are a lot more isolated than what is currently expected, then that could also elevate fire weather concerns for Central and Southwest Montana.

As it stands there is a generalized concern for elevated fire weather conditions starting on Friday but much of the threat will not be determined until Thursday evening when it becomes clear which locations were able to pick up some wetting rain ahead of the incoming hot, dry, and windy conditions. -IG/thor

HYDROLOGY

Today the Weather Prediction Center (WPC) has issued a Slight Risk (15% chance for flash flooding within 25 miles of a point) for flash flooding across most of Southwestern Montana. Between the I-90 corridor and a line between Augusta to Great Falls to Lewistown WPC has issued a Marginal Risk (5% chance for flash flooding within 25 miles of a point)for flash flooding today. In addition across the mountains of Southwestern Montana there is a 50 - 70% chance for rainfall rates in excess of one half inch per hour today. In addition there is around a 50% chance for rainfall rates in excess of three quarter of an inch per hour across the mountains of Southwestern Montana today. There is a 20 - 40% chance for an inch of rain or greater across the mountains of Southwestern Montana today. As a result a Flash Flood Watch remains in effect for the mountains south of I-90 through midnight tonight. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 62 96 63 98 / 10 10 20 0 CTB 58 94 62 93 / 10 10 10 0 HLN 62 94 63 97 / 30 20 10 0 BZN 58 91 60 97 / 50 20 20 0 WYS 50 82 50 87 / 70 30 20 0 DLN 55 87 57 92 / 60 20 20 0 HVR 60 99 64 102 / 0 10 10 0 LWT 57 90 60 95 / 10 30 10 10

TFX WATCHES/WARNINGS/ADVISORIES

Extreme Heat Watch from Friday afternoon through Sunday evening for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Hill County-Northern Blaine County.

Flood Watch until midnight MDT tonight for Gallatin and Madison County Mountains and Centennial Mountains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains.