textproduct: Great Falls

KEY MESSAGES

- Showers and thunderstorms diminish this evening, only to return on Wednesday.

- Slow warming trend Tue thru Fri, before turning significantly cooler this weekend.

- Periods of rain and mountain snow this weekend, with some areas receiving over an inch of liquid.

DISCUSSION

/Issued 1158 AM MDT Mon Jun 22 2026/

- Meteorological Overview: An upper level disturbance continues to move from west to east across the CWA. This is resulting in scattered showers/thunderstorm, mostly north of the I-90 corridor from Butte to Bozeman. The main impact from the storms today will be lightning/brief heavy rainfall, but some small hail will also be possible. The storms should diminish this evening, as drier air starts to move in from the west. Some patchy fog is possible by Tue morning, but too low of a probability to include in the forecast at this time.

For Tue thru Fri...expect a slow warming trend through this period, with afternoon temperatures going just a bit above normal by Friday. However, the trend has been for temperatures to not be quite as warm as previously forecasting, and some adjustment downward in temperatures for later this week is possible over the next few days. Just a small upper level ridge builds over the CWA on Tue, this will allow for a dry day across the CWA. By Wed afternoon, the ridge flattens a bit, for a few showers/thunderstorms to redevelop. The storms will become more numerous by Thursday afternoon, as the airmass also becomes a bit more unstable. There is a short break in thunderstorm activity on Friday morning, but more storms return by Friday afternoon ahead of the next upper level trof.

The first summer storm of the season looks to occur this weekend, as a slow moving upper level low is forecast to move across the Pacific Northwest and into the Montana area over the weekend. There will be plenty of moisture for this system to work with, along with much cooler air. Thus snow levels will range from about 7000 to 8000 feet by Sunday over much of the CWA. The forecast models are differing in where the heaviest precipitation will fall over the CWA, but overall, it is looking like the CWA will have much below normal temperatures and fairly wet conditions this weekend. It is looking like the precipitation will likely continue into Monday over portions of the CWA as well, just depending on the exact track of the upper level low.

- Forecast Confidence & Scenarios: Thunderstorm severity the next few days -> overall, mostly generally thunderstorms are expected today and on Wednesday. A stronger storm is possible, but the probability for any severe storms over the next few days is generally less than 5 percent.

For Thursday and Friday, the airmass will be a bit more unstable later this week, thus a severe storm can not be ruled out.

Strong winds -> Surface winds will increase ahead of the trof on Friday. At this time the strongest winds look to affect the Ennis valley on Friday afternoon. The probability of 60 mph wind gusts is only 20 percent this time, thus we will continue to monitor the trends of the gusty winds over the next few days.

Weekend rain/mountain snow/cooler temperatures -> Overall the main weather impact this weekend will be the much cooler temperatures and periods of precipitation. The airmass will be cold enough to support snow, even though it is late June, especially for elevations above 7000 feet. The probability of 1 inch of snow peaks around 70 percent for elevations above 7000 feet. The high end scenario has about 3 to 5 inches of snowfall at the peaks around the Pony and Big Sky mountains. (The Big Sky peaks goes up to 11,000 feet though.) Impacts should mainly be for those unprepared for winter conditions and recreating at higher elevations. In terms of liquid, there is up to a 50 percent chance of 1 inch of liquid at lower elevations and a 70 percent chance in the mountains this weekend. Thus this would be a very beneficial weather system for areas that receive these higher amounts, but again, only about 50 percent of the area will get one inch or more of precip, with the remaining are likely getting between a half inch and an inch of liquid. Additionally, the forecast models keep shifting which part of the CWA will get the higher precip amounts, whether it is North Central or Southwest MT, thus confidence is a bit low right now in pinpointing who gets the higher precip this weekend. Brusda

AVIATION

23/00Z TAF Period

Scattered showers and thunderstorms will continue to linger around Central and North-Central MT before dissipating around 04Z. An isolated shower could fall as far south as the Helena area. Ceilings will be low at times over North Central MT, with MVFR ceilings likely into the early morning hours, along with mountains obscured over Central/North Central MT. A low cloud deck will dip south over the Hi-Line from the Canadian border around 10Z, creating IFR conditions at times at KCTB and KHVR. Conditions improve between 16Z-18Z.

Over the Southwest MT terminals, generally VFR conditions are expected through the period. The exception will be around 12z Tue, when some patchy fog could develop in the valleys for a short time. However, it is too low of a probability to include at a terminal site at this time. -Brusda and Dzomba

PRELIMINARY POINT TEMPS/POPS

GTF 43 71 48 75 / 30 0 0 10 CTB 39 70 45 73 / 10 0 0 0 HLN 45 76 51 79 / 10 0 0 10 BZN 42 77 47 78 / 10 0 0 10 WYS 35 77 39 77 / 0 0 10 40 DLN 42 78 47 79 / 0 0 0 20 HVR 43 71 44 75 / 10 10 0 0 LWT 40 67 42 69 / 30 0 0 20

TFX WATCHES/WARNINGS/ADVISORIES

None.