977 FXUS65 KTFX 130518 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1118 PM MDT Tue Aug 12 2025 Aviation Section Updated. .KEY MESSAGES... - Very warm, dry and windy conditions on Wednesday will bring an elevated fire weather risk. - Isolated thunderstorms with gusty winds and little precipitation are expected across primarily southwest Montana late today and again Wednesday. - Cooler temperatures are expected Thursday with seasonably warm conditions prevailing this weekend. && .UPDATE... /Issued 821 PM MDT Tue Aug 12 2025/ A small update was posted this evening, mainly to draw out the PoPs near and east of Monida Pass along the ID border. Showers here have lingered into the early evening and should diminish over the next couple hours. Additional shower activity back in far eastern OR has a low-end opportunity to result in a brief shower across SW MT late tonight. Confidence in timing and location of any of this shower activity was too low to warrant raising PoPs at this time, especially given the low likelihood of these showers resulting in accumulating precipitation. -AM && .DISCUSSION... /Issued 821 PM MDT Tue Aug 12 2025/ - Meteorological Overview: A fairly zonal west to east flow is in place across the Northern Rockies and MT through the rest of the work week as upper level ridging gradually retrogrades westward toward the SW US and upper troughing lingering off the west coast ejects several waves by to our north across Canada. A subtle shortwave/upper jet disturbance embedded within WNW flow across the Northern Rockies tracks across SW MT late this afternoon and evening, which may lead to a few thunderstorms across primarily Madison and Gallatin counties. Cannot completely rule out some isolated convection further north across central/north-central MT, but a subsidence inversion around 600MB noted on the 18z KTFX sounding is likely to provide enough convective inhibition to keep the risk low and mainly limited to areas near the island ranges and Little Belts. Main concern with any thunderstorm activity late this afternoon and evening will be gusty downdraft/outflow winds due to high cloud-bases and dry low levels. On Wednesday, larger scale troughing shifting inland across BC/AB will compress/increase the westerly flow aloft across the Northern Rockies while also aiding int the development of surface/lee-side troughing in southern AB. Afternoon mixing will transport these stronger winds to the surface with widespread gusts exceeding 25-30 mph across the area and gusts in excess of 40 mph likely (>60% probability) along the Rocky Mtn Front and most of Glacier County. Temperatures will warm into the 90s across much of the area as well with low afternoon humidity leading to elevated fire weather conditions (See fire wx discussion for additional info). The risk for thunderstorms on Wednesday will mainly be limited to portions of SW MT along/south of I-90. A cold front moving south from Canada will spread cooler temperatures across north-central and central MT Thursday with warm and breezy conditions persisting in southwest MT still Thursday afternoon before these areas cool Thursday night. A southwest flow aloft sets up this weekend into next week as upper level ridging tries to build westward across the SW US while troughing remains in place near/off the west coast of Canada. Temperatures will warm back to near and slightly above seasonal averages this weekend before warming further early next week. Some moisture is likely to become entrained into the flow and bring low chances for daily thunderstorm development as early as Sunday, but there is still considerable uncertainty at this time with specifics of moisture and disturbances to move through area Sunday through early next week. - Forecast Confidence & Scenarios: Thunderstorm risk this afternoon/evening ranges from 10-30% across Madison and Gallatin counties with highest probability from Yellowstone NP into southern Gallatin county. There is a 10-15% risk of thunderstorms across portions of north-central MT near the Canadian border and island mountain ranges. Hoenisch && .AVIATION... 13/06Z TAF Period VFR conditions will prevail at all terminals. The primary concern during this TAF Period will be gusty winds at all terminals beginning after 13/15Z and lasting through much of the rest of this TAF Period. At the KEKS and KWYS terminals there is a 20 - 30% chance for showers and thunderstorms between 13/19Z and 14/00Z. Any thunderstorms will produce gusty, erratic winds and frequent lightning. There will be isolated instances of low-level wind shear across North-central Montana between 14/02Z and 14/06Z. There is less than a 10% chance for fog to form at the KWYS terminal Wednesday morning. -IG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .FIRE WEATHER... Fire weather concerns will be elevated on Wednesday with very warm afternoon temperatures and low afternoon humidity combined with breezy to windy conditions across much of the area. The most critical conditions are expected across southwest MT where fuels are drier. Further north across most of central/north-central MT, fuels/fire danger are not at critical thresholds following recent precipitation, but the very warm, dry and windy conditions will bring an elevated risk for fire spread in areas where fuels may be locally more receptive. Hoenisch && .PRELIMINARY POINT TEMPS/POPS... GTF 60 92 56 79 / 10 0 0 0 CTB 56 87 51 71 / 0 0 10 0 HLN 59 93 57 86 / 0 0 0 0 BZN 55 94 53 89 / 10 10 0 0 WYS 43 84 41 81 / 20 30 10 10 DLN 52 90 49 87 / 10 10 0 0 HVR 59 94 55 76 / 10 0 0 0 LWT 58 89 54 78 / 10 0 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... && $$ http://www.weather.gov/greatfalls