222 FXUS65 KTFX 251119 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 519 AM MDT Sun May 25 2025 Aviation Section Updated. .KEY MESSAGES... - Aside from an isolated afternoon shower or storm over higher terrain, dry and warm conditions through Monday afternoon. - Shower and thunderstorm activity increases late Monday through Tuesday, with a few stronger storms containing gusty winds, brief downpours, and small hail. - Temperatures generally trend above average next week. && .DISCUSSION... /Issued 243 AM MDT Sun May 25 2025/ - Meteorological Overview: A ridge of high pressure is moving into the Northern Rockies this morning under mostly clear skies. Patchy fog development has been very limited so far this morning thanks to easterly breezes and or drier air mixing to the surface. There will still be an opportunity for 'sunrise surprise' fog development through the mid-morning hours, mostly along the Milk River Valley where winds are light and dew point depressions are currently less than 3 degrees. The latest probabilistic guidance also paints the Milk River Valley with a 30 to 50% chance for visibility dropping below a half mile. Otherwise, expect a mostly sunny, warm day with only a slight chance for an isolated afternoon/evening shower/storm over the higher terrain of Central and Southwest Montana. Most lower elevation locations will see their high temperatures peak in the upper 70s to lower 80s on Monday prior to a weak mid- level low pressure system temporarily knocking temperatures down a few degrees on Tuesday. This system will also bring an increase in scattered shower and thunderstorm activity late Monday afternoon through Tuesday. Given this system will be weakening while cutting off from the main trough, there will be a more confined and weakening area of ascent and wind shear to compliment available moisture and instability. None the less, a few storms will be on the stronger side with gusty winds, brief downpours, and small hail, especially during the evening and early overnight hours on Monday. Ridging aloft will be the primary weather influencer Wednesday into next weekend with mostly dry conditions and temperatures running above average; however, there looks to be another weak mid- level low that will undercut the ridge Thursday into Friday and bring another increase in shower and thunderstorm activity. - RCG - Forecast Confidence & Scenarios: Showers and thunderstorms Monday and Tuesday... Shower and thunderstorm activity on Monday and Tuesday is largely dependent on the evolution of a closed low splitting off from a northward moving Pacific shortwave. This system will offer weakening ascent and wind shear as it moves into the forecast area; however, diurnal heating will be strong Monday afternoon and forecast soundings show inverted V profiles indicative of dry sub-cloud layers and potential gusty thunderstorm winds. The most aggressive storms should occur late Monday afternoon through the early overnight hours near the Continental Divide and Southwest Montana with weaker activity farther east. The strongest storms will be capable of localized strong, gusty winds in excess of 40 mph, brief downpours, and small hail. Additional scattered showers and thunderstorms are expected on Tuesday as the low weakens further while drifting over the forecast area. - RCG && .AVIATION... 25/12Z TAF Period Ridging aloft will maintain mostly VFR conditions over the next 24 hours; however, patchy/isolated fog development and low stratus is being observed this morning over the higher terrain east of KBZN and KWS1. There also have been some fog patches in the vicinity of KHVR where the chances for visibility falling below 3 miles is around 30% through 25/15Z. East to southeasterly winds may gust in the 10 to 20kt range at KHVR and KCTB this afternoon and tonight. - RCG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 76 46 81 52 / 0 0 10 60 CTB 76 45 80 49 / 0 0 20 50 HLN 78 48 81 52 / 0 0 30 70 BZN 74 42 78 47 / 0 0 20 60 WYS 69 33 71 38 / 20 10 30 60 DLN 72 43 76 46 / 0 0 30 50 HVR 77 47 78 48 / 0 0 0 20 LWT 69 43 73 46 / 10 0 10 20 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls