Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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396 FXUS65 KTFX 170606 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1200 AM MDT Mon Jun 17 2024 Aviation Section Updated .SYNOPSIS... Cooler than normal temperatures prevail, while the next weather producer enters the region. Mountain snow and widespread low elevation rain are forecast, through the early part of the coming week. Low elevation high temperatures reach back into the 70s by Thursday. && .UPDATE... Only minor adjustments needed to this evening`s forecast period. Cooler Canadian air has already pushed south over the plains of North Central Montana, so have lowered hourly temperatures to reflect this. Mid-level moisture is increasing from the southwest ahead of the approaching system, but no precipitation has been observed yet west of the Continental Divide, so the timing of the precipitation moving into the area mainly after midnight appears to be on track. -Coulston && .AVIATION... 17/06Z TAF Period Showers will move in in overnight (already ongoing at KGTF) and into the morning hours across all terminals. Ceilings will transition to VFR to MVRF with initial showers, and then to IFR conditions (by late morning at KGTF and during the evening for KBZN, KEKS, KWYS, and KLWT). Widespread showers (possibly some light snow showers mixing in at KWYS) will last through the TAF period. There`s a 10- 30% of a few embedded thunderstorms with showers that can drop visibilities to MVR/IFR Monday this afternoon. Mountain obscuration will be persistent through the TAF period, with snow falling above 6,000ft. -Wilson Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 550 PM MDT Sun Jun 16 2024/ Today and Tomorrow...Cool low elevation temperatures are forecast. Areas of light rain are forecast north of the Hi-Line through this afternoon. This evening, the next weather producer enters the region, beginning with precipitation falling across southwest Montana. The forecast is for low elevation rainfall, with accumulating snow forecast at elevations, generally, above 6000 feet. - Fogleman Tomorrow, continued...Precipitation will become more widespread and heavier Monday morning with the upper level low moving passing through the region. There may be a few embedded thunderstorms with precipitation on Monday/Tuesday afternoon due to a little amount of instability present. Precipitation lingers into Tuesday along another wave passing through the region. Snow probabilities in the mountains are between 30-50% for exceeding 8" of snow. Considering the bulk of the snow being above pass level and probabilities for accumulations to reach winter warning criteria (9 inches) remain on the lower side, I have opted to transition the Winter Storm Watches for mountain zones into Winter Weather Advisories. Another change I`ve made to the winter highlights is to move up the timing to 6pm Sunday to 6pm Tuesday to account for the earlier start and end times for precipitation. Greatest QPF amounts look to set up across Central MT, where they have around a 50% of exceeding 1". Most other lower elevations across the CWA have at least a 50% of exceeding 0.25". In terms of possible higher end QPF amounts, the 75th NBM percentile ranges between 1.25-1.5" across Central MT and 0.35-0.75" across most other lower elevations. With the upper level low bringing down colder air, cold overnight temperatures are forecasted for Monday and Tuesday morning. Tuesday morning wind chills in the mountains can drop down to the teens and 20s. Those in the backcountry should prepare for cold/raw conditions. Wednesday and looking beyond...The main upper level low will move off to the east, and a zonal/southwest flow aloft pattern will settle in behind for the remainder of the week. There looks to be enough moisture around and small disturbances that passes through to keep low chances of precipitation daily. With the southwest flow aloft bringing in warmer air, temperatures will gradually warm up through the weekend. By Saturday, lower elevations have a 60-80% of high temperatures reaching 80 degrees or higher. -Wilson && .PRELIMINARY POINT TEMPS/POPS... GTF 42 49 40 57 / 40 90 80 80 CTB 37 53 37 55 / 20 80 60 70 HLN 44 54 42 63 / 60 100 80 80 BZN 41 56 37 59 / 30 90 90 70 WYS 38 52 30 52 / 20 70 70 60 DLN 39 52 34 56 / 30 90 70 50 HVR 42 57 42 61 / 10 90 70 60 LWT 38 52 35 55 / 30 90 90 80 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 6 PM MDT Tuesday for Big Belt, Bridger and Castle Mountains-East Glacier Park Region-Elkhorn and Boulder Mountains-Gallatin and Madison County Mountains and Centennial Mountains-Little Belt and Highwood Mountains- Northwest Beaverhead County-Southern Rocky Mountain Front. && $$ http://www.weather.gov/greatfalls