textproduct: Great Falls

KEY MESSAGES

- Daily chances for scattered showers and thunderstorms through Friday with a chance that a couple may become severe.

- Concern for flash flooding across portions of Southwest and Central Montana through this evening.

- Drier, warmer, and breezy conditions expected over the holiday weekend.

DISCUSSION

/Issued 256 PM MDT Wed Jul 1 2026/

- Meteorological Overview:

Scattered thunderstorms are already underway across Southwest Montana with gusts up to 45 mph observed. These thunderstorms will slowly become more numerous into Central Montana as the day progresses with the main threats being strong winds, hail, heavy downpours, and cloud to ground lightning. A couple storms may become severe but the limiting factor this afternoon will be the lack of shear across the region. With shear turning out to be less than 20kts across a good portion of the region, storm motion is expected to be on the slower side which will increase the potential for flash flooding, especially if the thunderstorms start to train.

Similar conditions prevail on Thursday and Friday with widely scattered showers and thunderstorms, but there will be a lack of a defined shortwave on Thursday and on Friday the shortwave positioning looks to be a little too far east for widespread activity. Flat ridging starts to build in and bring warmer temperatures and drier conditions for the holiday weekend; however, a mid-level trough passing north of the Canadian border looks strengthen the westerly flow aloft and combine with deep layer mixing for breezy to windy conditions. Saturday, Independence Day, will be the windiest day with the highest probabilities for 40 mph wind gusts or higher along the Rocky Mountain Front. The greatest impacts from the winds will be for holiday related activities and for outdoor recreation. Recent rainfall and surface greening should preclude fire weather concerns despite the low afternoon humidities.

Mid-level heights continue to rise and bring summer like temperatures early next week. The only caveat will be a southwesterly flow aloft developing again in response to a trough moving onto the PAcific NW coast. Shortwaves look to interact with building instability for increased shower and thunderstorm activity next Monday and Tuesday. The ECMWF Extreme Forecast Index (EFI) is already beginning to highlight unusually high CAPE and shear availability for strong to severe storms for these days should this pattern come to fruition. -RCG/thor

- Forecast Confidence & Scenarios:

Thunderstorms Today:

Showers and thunderstorms are already underway across Southwest Montana and are expected to become more numerous into Central Montana as the day continues. In general, most of these storms will produce dime-size or smaller hail and maximum wind gusts of 45 mph. That being said, there is a chance a couple could become severe. The main threat across the region will be strong winds but Southwest Montana, in particular, will carry the highest chances for larger hail if it occurs.

Additionally, these storms are expected to be relatively slow- moving which may lead to some minor flooding in typical flood- prone areas. Overall, Southwest Montana has been dry over the past couple months compared to the rest of the region. This means that, while some isolated ponding and flooding of flood-prone areas is possible, widespread, significant flooding is generally not expected across a good portion of Southwest Montana. The exception to this are the areas that are currently under a Flash Flood Watch. These areas, including northwest Beaverhead county, the Boulder Hill region, and the Horse Gulch burn scar have additional compounding concerns that may make any heavy rainfall from thunderstorms a flood threat. A more in-depth discussion on this can be found in the HYDROLOGY section.

Thunderstorms Thursday/Friday:

Additional rounds of thunderstorms are expected Thursday and Friday afternoon. Right now, conditions look a bit marginal for development in our portion of Montana. Coverage is likely to be isolated to scattered at best and the main concerns will be lightning and gusty winds impacting those who are recreating outdoors leading up to the holiday weekend.

Warm, Dry, Breezy This Weekend:

In general no major impacts to the public are expected over the holiday weekend. Temperatures are expected to warm into the 80s this weekend across the lower elevations. While this puts us closer to the seasonal average, it will be comparatively warmer than what we have experienced this past week. Combined with the influx of folks spending a lot of time outdoors, there are some minor concerns for heat-related illness during the day particularly for those that are sensitive to the heat.

Breezy and dry conditions are expected through the afternoon which could have some minor impact on afternoon holiday plans but significant synoptic winds are not expected. The winds will be pretty diurnally driven so they should taper off by the time the bigger fireworks displays are occurring but folks in general should still exercise firework safety, even in areas that have been wetter over the past week.

Warmer and More Active Next Week:

While there is still a bit of uncertainty as to how early next week will play out, there are still strong signals in the long- term models that we may be heading towards a warmer period with daily chances for afternoon showers and thunderstorms. -thor

AVIATION

02/00Z TAF Period

Showers and thunderstorms will continue through this evening, mainly across Southwest and Central MT. These storms may produce gusty, erratic winds as well as frequent lightning. VFR conditions will generally prevail throughout the TAF period, with MVFR conditions and mountain obscuration possible at times due to a passing shower or thunderstorm. Thunderstorms dissipate after 06Z, followed by calm conditions throughout the rest of the TAF period. -Dzomba

HYDROLOGY

Many Glacier Area: Flooding has now decreased to minor levels mainly impacting campgrounds and some trails. Given that flooding has decreased below warning levels, the Flood Warning has been replaced with a Flood Advisory through Thursday afternoon. Additional rainfall is not expected over the next 24 hours which should help ease some concerns and allow the area to continue draining and recovering.

Horse Gulch Burn Scar: Slow-moving thunderstorms with the potential to bring heavy rain are possible along the Horse Gulch burn scar. The primary concern outside of flash flooding will be debris flows. Given the past behavior of the burn scar, the amount of precipitation received in the last few days, and the amount of precipitation possible according to hi-res model guidance, the decision was made to put out a Flash Flood Watch for the burn scar through the evening. One of the major things to consider for those living and recreating in the area is even if you do not personally receive rain, if any higher portion of the burn scar receives enough rain to flood or start a debris flow, it can quickly move downhill and cause significant impacts. Therefore, be aware of your surroundings and have a way to receive warnings in case they are issued.

Northwest Beaverhead County and Boulder Mountains: Slow-moving thunderstorms over mountainous terrain that has previously received at least a couple inches of precipitation could cause flash flooding. Hi-res model guidance has pointed out these portions of Southwest Montana as having the highest probability for higher rainfall rates and amounts. In particular with the mountains in northwest Beaverhead county, there is a concern for flooding with rain falling on top of snow at the higher elevations which can then become increased runoff further downstream. For now this situation will be monitored carefully but the watch will remain in effect until midnight to address some of the main concerns with the potential for flash flooding. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 51 77 51 79 / 40 0 0 20 CTB 47 73 48 74 / 0 0 0 0 HLN 50 76 52 78 / 50 20 10 30 BZN 45 76 48 77 / 50 10 10 20 WYS 37 72 39 73 / 20 0 10 10 DLN 44 75 46 76 / 60 0 0 10 HVR 52 80 52 81 / 20 10 0 10 LWT 47 74 48 74 / 60 20 20 60

TFX WATCHES/WARNINGS/ADVISORIES

Flood Watch until midnight MDT tonight for Elkhorn and Boulder Mountains-Northwest Beaverhead County.

Flash Flood Watch until 10 PM MDT this evening for Big Belt, Bridger and Castle Mountains.