583 FXUS65 KTFX 130516 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1116 PM MDT Tue Sep 12 2023 ...Aviation Section Updated... .SYNOPSIS... Scattered rain showers across Southwest MT along the MT/ID border and isolated thunderstorms in higher elevations of Central MT this evening. Tomorrow has a similar weather pattern with a higher probability of scattered thunderstorms across Southwest Montana. Quiet weather returns beyond Thursday into early next week when our next weather system has potential to bring unsettled weather. Above normal temperatures returns for this weekend with highs in the 80s and near normal temperatures returns for next week. && .UPDATE... Main update for the overnight period was to increase coverage to scattered of continuing showers and thunderstorms across much of North Central and Central Montana. These showers and thunderstorms seem to be feeding off of lingering instability from today's heat and combining with the slow passage of a weak cold front. Although some of the storms could produce wind gusts up to 35 mph, hail and heavy rainfall are unlikely. The chance for showers will linger for a few hours after midnight, mainly over Central Montana, including the Great Falls area. Otherwise, the forecast is on track for a widespread chance of showers and thunderstorms again on Wednesday, along with gusty westerly winds and cooler temperatures. -Coulston && .AVIATION... 1116 PM MDT Tue Sep 12 2023 (13/06Z TAF Period) VFR conditions prevail across all terminals through the morning hours under generally mid- to high-level clouds. After 18z, terminals in Southwest Montana, namely KBZN, KWYS, and KEKS, will see brief periods of MVFR conditions in showers and thunderstorms as unsettled weather moves in associated from an upper-level trough from the Pacific. In addition, a cold frontal passage propagates over the Northern Rockies, resulting in a shift of more westerly winds. Periods of gusty winds from this shift will occur along the Hi-Line, impacting KCTB and KHVR, as well as portions of the central plains, impacting KLWT. - Pierce Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 640 PM MDT Tue Sep 12 2023/ Rest of Today through tomorrow... Scattered rain showers have developed over the MT/ID border of Beaverhead County that will continue to move through the MT/ID border line this afternoon and evening. Any kind of precipitation will be less than 0.05 inches with those showers. Later this afternoon over Central Montana, isolated rain showers and a rumble of thunder have potential to develop. Probability of thunder for today is less than 20 percent with the higher end probability (20 percent) for an isolated thunderstorm being in the higher elevations across Central Montana such as the Little Belt Mountains. Otherwise, isolated rain showers continue through the overnight period with probability of precipitation being less than 0.05 inches is between 70 and 90 percent. Primary concern for any developed thunderstorm today is going to be lightning. For tomorrow, we start off the morning with quiet weather then rain shower and thunderstorm activity increases after noon for Central and Southwest Montana. Probability of thunder is between 30 and 50 percent for tomorrow between 3 PM and 9 PM. Primary concerns for any developed thunderstorm tomorrow are lightning, a heavy downpour and small accumulating hail. A quick moving upper level trough is the primary responsibility for the unsettled weather as it moves off from the Pacific Northwest across western and Southwest Montana through Wednesday evening. This will bring scattered rain showers across North Central Montana as it exits the region. While not everywhere will see accumulating rainfall and primary locations that do are going to be south of the I-90 corridor from Three Forks to Bozeman, locations that do have between 40 and 60 percent probability of seeing between 0.01 inches and 0.1 inches of precipitation, with heavier amounts in thunderstorms. Thursday through early next week... Upper level ridging builds back in for a quiet weather pattern the rest of this week as the upper level trough moves eastward with near normal temperatures for Thursday and Friday (average high temperatures in the 70s) then warming up for the weekend with temperatures in the 80s. From the latest NBM (National Blend of Models) 4.1 probabilistic data, Sunday and Monday across North Central and Southwest Montana valleys have over 90 percent probability of afternoon high temperatures being greater than 80 degrees. After Monday, ensemble model guidance is suggesting an upper level trough will build over the Pacific Northwest and move over Montana Tuesday into Wednesday next week bringing unsettled weather conditions at the surface and near normal afternoon high temperatures. Webb && .PRELIMINARY POINT TEMPS/POPS... GTF 54 76 50 74 / 20 10 10 0 CTB 51 72 46 73 / 0 20 10 0 HLN 56 78 51 77 / 30 20 10 0 BZN 50 73 44 72 / 10 40 20 10 WYS 39 66 35 64 / 10 70 40 20 DLN 46 69 41 69 / 10 30 10 0 HVR 54 81 47 76 / 30 10 10 10 LWT 51 73 45 70 / 20 20 10 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls