815 FXUS65 KTFX 121820 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1220 PM MDT Thu Jun 12 2025 Aviation Section Updated. .KEY MESSAGES... - An unsettled pattern looks to continue into at least early next week, with daily opportunities for showers and thunderstorms across most areas. - The day most favored for strong to severe thunderstorms looks to be Friday, with the threat continuing in portions of the region into Saturday. - Confidence in strong to severe thunderstorms decreases for late weekend into early next week, though the risk is certainly non- zero. && .UPDATE... /Issued 1008 AM MDT Thu Jun 12 2025/ 10:05 AM : The Dense Fog Advisory for portions Judith Basin County was allowed to expire at 0900, but the Fergus County portion of the advisory was extended until 1100 due to on-going visibilities below 1/4 mile here. Visibilities are slowly beginning to improve as of this writing across Fergus County, and it will be our intention to expire the Dense Fog Advisory at 1100 here. Otherwise the remainder of the forecast remains on track and no other updates are planned. - Moldan 6:47 AM : Early morning update has been published, mainly to add mentions of dense fog across portions of Judith Basin and Fergus Counties where MDT cameras, satellite imagery, and local spotters are reporting/supporting visibilities below one quarter of a mile. A Dense Fog Advisory has also been issued for this area until 9 AM this morning after which time we will re-evaluate the need for either an extension of the advisory or whether it can expire. Patchy fog, locally dense, was also occurring across portions of Southwest Montana this morning. Given the patchy nature of this fog here I have messaged the reduced visibilities with a Special Weather Statement. - Moldan && .DISCUSSION... /Issued 1008 AM MDT Thu Jun 12 2025/ - Meteorological Overview: Persistent troughing off the Pacific NW coast and associated southwesterly flow aloft will be the main driver of weather across the region through at least Monday. Waves rippling through the Southwesterly flow aloft will combine with ample surface moisture for mainly afternoon and evening showers and thunderstorms. Showers and thunderstorms will be around through the overnight and into the morning hours at times, but these timeframes are overall less likely for precipitation. Upper level support today appears to be the least favorable compared to the next several days, as subtle shortwave riding passes through. That said, ample surface moisture, surface heating, and increased shear (Up to around 30kts or so effective shear) will result in better organized showers and thunderstorms today. The lack of higher shear keeps confidence low for organized severe thunderstorms today, though they cannot be ruled out. In the meantime, a mix of showers and more stratiform rain will continue across eastern and northern portions of the plains into daytime hours today. This should help decrease overall smoke amounts near the surface, though will not eliminate it. Heading into Friday a shortwave pivoting through the Pacific NW troughing ejects toward the Northern Rockies in the late morning through afternoon hours. Surface moisture from previous precipitation across the plains and adjacent areas as well as advection in from the east near the surface should be sufficient for ample instability, even with cooler surface temperatures in place. Increased southwesterly flow aloft overtop easterly surface winds will help increase shear above 40 kts, helping to support a greater threat for organized severe weather. Strong wind gusts in excess of 58 mph and large hail are the primary concerns with the stronger thunderstorms Friday. The setup is largely the same for Saturday, though the best instability does look to be confined to eastern areas. Gusty winds and hail will continue to be the primary concern with the strongest thunderstorms that form. Heading into Sunday and into Monday the southwesterly flow aloft remains. Confidence in timing any shortwaves that would aid in shower and thunderstorm development decreases quite a bit. That said, lingering surface moisture and respectable shear profiles suggest at least a low-end threat for stronger thunderstorms will remain heading into early next week. Cluster guidance for the middle of next week favors the southwesterly flow aloft persisting. Where confidence lowers significantly is whether this is a more cyclonic or anti-cyclonic southwesterly flow. Regardless, at least low-end chances for afternoon and evening showers and thunderstorms look to persist heading into the middle of next week. -AM - Forecast Confidence & Scenarios: So far the bulk of the more persistent/stratiform precipitation has been in the Lewistown area and away from the Hi-Line. Guidance still does show a window later this morning for the rain to make it up that way still, so I have not lowered PoPs just yet. Otherwise the greatest uncertainty in the forecast is related to just how much instability develops each day late weekend into early next week. There remains significant discrepancies between magnitude of instability that develops as well as where exactly it develops. As mesoscale details become better resolved over the next couple days, confidence in how Saturday and onward will play out will subsequently increase. -AM && .AVIATION... 12/18Z TAF Period Widespread rain will slowly exit off to the east across the North-Central MT plains this afternoon. This will continue to bring IFR cigs/vis at times at KCTB, KHVR, and KHVR through 12/22z. Everywhere else, there will be isolated showers/thunderstorms this afternoon and evening. Lightning will be more isolated today, so it wasn`t included in all TAF sites due to the low chances for it to hit right over the terminal. As precipitation clears out tonight, cloud cover lingers. However, weak subsidence and low level moisture from precipitation will try to develop fog across the North-Central MT plains. With a broken cloud layer, there remains uncertainty whether the fog develops or it remains more of a low stratus deck. -Wilson Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 70 50 75 52 / 70 30 70 60 CTB 66 48 72 46 / 100 40 50 50 HLN 77 52 77 52 / 60 40 70 50 BZN 78 49 79 48 / 30 20 40 30 WYS 71 39 74 37 / 30 30 10 10 DLN 75 46 76 43 / 20 30 40 30 HVR 64 49 75 52 / 90 30 80 50 LWT 62 48 71 50 / 70 40 80 60 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls