textproduct: Great Falls

KEY MESSAGES

- Scattered showers and thunderstorms, a few of which may be severe, Saturday and Sunday.

- Elevated fire weather conditions Sunday as breezy winds develop in most areas behind a front.

- On the warmer side of average next week with scattered showers and thunderstorms most days.

DISCUSSION

/Issued 1154 PM MDT Fri Aug 21 2026/

- Meteorological Overview:

The ridge axis associated with a high amplitude upper level ridge across the Northern Rockies will begin shifting east of the area late tonight and into the morning Saturday. This will eventually result in a southwesterly flow aloft which will foster scattered showers and thunderstorms this weekend ahead of a cold front. In the meantime the remainder of the afternoon looks dry and warm. A few showers or thunderstorms cannot be ruled out this evening along the Continental Divide in Southwest Montana, but those probabilities are low.

Flow aloft into tomorrow has a much more southerly component than westerly, at least initially, which will aid in advecting in monsoonal moisture. Combine this with ample flow and forcing aloft from an approaching trough across the Pacific NW and scattered afternoon and evening thunderstorms will develop as a result. There looks to be enough of a balance between drier inverted-V lower level profiles and ample moisture aloft to result in both a gusty wind and excessive rainfall risk Saturday afternoon and evening. Forcing associated with the approaching upper level trough from the Pacific NW will keep at least widely scattered showers and thunderstorms around through the overnight Saturday into Sunday morning.

Heading into Sunday the core of the upper level disturbance passes just north of the region, which will foster both a thunderstorm threat and fire weather threat. The magnitude and duration of each of these threats will be dictated by just how quickly an associated cold front moves through.

Heading into next week Monday looks to be a slightly cooler day behind a front, but temperatures quickly trend back warmer by Tuesday. Persistent southwesterly flow aloft will keep at least isolated showers and thunderstorms in the forecast through next week. -AM

- Forecast Confidence & Scenarios:

Thunderstorms Saturday:

There is still a bit of a north-south discrepancy with respect to where showers and thunderstorms develop through the day. Given precipitable water values near or in excess of an inch, wherever these thunderstorms develop will have the risk for at least briefly heavy rain. Areas of greatest concern for localized flash flooding will be in urban areas and over and near burn scars. The threat for gusty winds will also be around, with a few gusts in excess of 58 mph not out of the question.

Sundays fire weather and thunderstorm risk:

A quicker front would increase the duration of winds and related fire weather concerns, while a slower front would allow for greater instability to form and result in a greater thunderstorm risk. The kinematic environment for thunderstorms ahead of the front would be sufficient for a few organized thunderstorms, including a supercell or two, capable of gusty winds and hail. -AM

AVIATION

22/06Z TAF Period

Predominantly VFR conditions across the region with some mild slant range visiblity reductions due to smoke in Southwest MT. Scattered showers and thunderstorms are expected over far Southwest MT until 09Z creating strong gusts up to 40 KT and some cloud-to-ground lightning. A more organized line of widespread and stronger thunderstorms from the south will progress northeastward through the region Saturday afternoon after 21Z until late Saturday night bringing heavier rainfall and strong gusts over 40 KT with the potential for some to be severe.

For KGTF: VFR conditions are expected overnight until light showers and thunderstorms arrive late morning follwed by stronger thunderstorms in the evening from 02Z to 04Z. Winds will be light and variable overnight then shift southwesterly after 16Z. Hazards for the thunderstorms will be gusty outflows of up to 40 KT as well as localized heavy rain and lightning. - Akins

FIRE WEATHER

The fire weather concerns begin when isolated showers and storms with cloud to ground lightning and little precipitation pass through this evening into tonight. Even though this activity will be isolated, some new fire starts can't be ruled out. More productive storms move in on Saturday, but again the presence of cloud to ground lightning may ignite new fire starts. The most concerning day will be on Sunday when a surface front brings gusty westerly winds amid continued very warm and dry conditions. The timing of this front will ultimately determine how long the dry windy conditions persist. The latest NBM probabilistic guidance highlights large areas of north-central and portions of southwest Montana with over a 60% chance for wind gusts over 30 mph. Although the fuels aren't quite as dry as they were in earlier in the month, elevated fire conditions will be present and the wind may be enough to ignite any lightning caused hold over fires from Friday and Saturday's storms. - RCG

HYDROLOGY

The combination of increased monsoonal moisture from the south and better surface Tds working in near the surface from the east will result in the risk for heavy rainfall from thunderstorms Saturday. Should confidence rise in these heavier thunderstorms occurring over a particular burn scar or urban area, a flash flood watch may become necessary. The better moisture begins to exit Sunday, which will close the window for the potential for excessive rainfall for the near term. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 60 90 61 89 / 0 30 40 20 CTB 55 85 57 81 / 0 30 20 20 HLN 61 90 57 87 / 10 30 60 30 BZN 59 87 53 86 / 10 50 40 40 WYS 52 81 45 78 / 20 50 40 30 DLN 58 86 52 85 / 20 40 60 10 HVR 60 93 61 93 / 0 20 10 40 LWT 58 88 59 89 / 0 20 30 40

TFX WATCHES/WARNINGS/ADVISORIES