


Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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110 FXUS65 KTFX 121050 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 450 AM MDT Sat Jul 12 2025 Aviation Section Updated. .KEY MESSAGES... - Hot and generally dry conditions expected through the weekend. - Chance for isolated thunderstorms along the Hi-Line Sunday evening. - Cooler and wetter conditions return Monday through Wednesday. && .DISCUSSION... /Issued 302 AM MDT Sat Jul 12 2025/ - Meteorological Overview: Northwest flow will continue through today and tomorrow with temperatures warming into the upper 80s to mid 90s across the lower elevations of north-central, central, and southwest Montana. Generally dry conditions are expected through the weekend outside of a 20-30% chance for isolated thunderstorms across the Hi-Line Sunday afternoon/evening. A strong cold front pushes through Monday into Tuesday bringing temperatures across north-central and central Montana down 10 to 15 degrees. There is a chance for widespread rain across much of north-central and central Montana with more isolated amounts down into southwest Montana through Wednesday. In the wake of the trough, temperatures will start to moderate with some warming expected by the weekend. - Forecast Confidence & Scenarios: Hi-Line Thunderstorms on Sunday: There are early indications from the RDPS and NAM 3km that there could be some thunderstorms along the Canadian border Sunday afternoon/evening with just enough CAPE and shear to cause problems. In lieu of more hi-res guidance, which does not quite go out far enough at this time, the most likely scenario is that most of the thunderstorm activity will stay north of the Canadian border. However, a few cells may turn south into Montana causing concern as those tend to be on the stronger side. The main concerns with any thunderstorm that develops would be strong winds and hail. Storm System Monday-Wednesday: Despite the start of this event only being a couple days out, there are still some drastic differences in how the models are handling both the timing and position of the upper level trough that is expected to move through the region. To give an idea on the current timing differences, the ECMWF has the trough axis over western Montana at 00Z Wednesday, the GDPS has this occurring at 06Z Wednesday, and the GFS has the trough axis reaching western Montana by 15Z Wednesday. To further add complications, the 06Z run of the NAM is suggesting the trough axis reaches western Montana by 09Z Tuesday, 12-24 hours ahead of the long-range models. Not to mention that while the ECMWF, GDPS, and NAM agree on the trough digging through much of the state, which would give us more moisture and higher rainfall amounts, the GFS flattens out the trough and keeps it generally above the International border which would almost completely dry out any potential rainfall in Montana. As it stands, the NBM is currently taking a middle-of-the-road approach but leaning on the wetter side of things with most of the precipitation falling north of a line between Helena and Lewistown and locations in southwest Montana receiving generally less than a tenth of a inch. Forecaster confidence-wise, it seems more of long-range models are pointing towards a wetter solution with the GFS remaining an outlier for now. Early indications at the end of the 06Z NAM confirm that there is fairly good confidence in north-central and central Montana receiving a wetting rain. Some of the current QPF amounts seem to be a little high but are not outside the range of possibilities with this event. The concerning factor is if the NAM is true, the trough is arriving much sooner than previously expected which may potentially throw some of the current forecast out of alignment. Right now, the confidence is that there is a trough and it will arrive in Montana. Beyond that, the models still have yet to agree on the finer details on how this event will play out. -thor && .AVIATION... 12/12Z TAF Period VFR conditions prevail under a few high clouds this TAF period. West to northwest surface winds develop late morning and early afternoon, though are not forecast to be overly gusty. -AM Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 91 60 94 58 / 0 0 0 10 CTB 85 56 88 55 / 0 0 0 20 HLN 91 58 94 61 / 0 0 0 10 BZN 91 53 94 55 / 0 0 0 10 WYS 81 41 85 44 / 0 0 0 10 DLN 87 51 90 53 / 0 0 0 10 HVR 91 58 94 59 / 0 0 0 20 LWT 85 55 90 55 / 0 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls