Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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605 FXUS65 KTFX 180505 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1105 PM MDT Mon Jun 17 2024 ...Aviation Section Updated... .SYNOPSIS... Cool and wet conditions continue through tonight and early tomorrow morning as a cold spring weather system moves through the area. After widespread showers on Tuesday, we will continue to have a few isolated to scattered afternoon showers and thunderstorms during the afternoons each day through the end of the week. && .UPDATE... Updated forecast is out. The main adjustment was to lower snow levels to valley floors over portions of Southwest MT, especially over Madison and Gallatin counties. Overall, the snowfall has been light for most areas today. It has been snowing, mostly above 7000 feet around Big Sky, Bridger, Kings Hill per web cams. For areas lower than 7000 feet, snow fell at times, but generally mostly melted out. Cooler air is working into the system currently, this will change the rain to snow over Southwest MT at all elevations a bit easier, as elevations in the Southwest area mostly above 4000 feet. Snow accumulations at the valley floors should be mostly limited to grassy areas, where an inch or two is possible. In the mountains, up to 5 inches is possible. Further north, the precipitation has become more scattered over North Central MT. Snow amounts tonight should be slightly lighter in the mountains, where up to 3 inches are possible. Thus the winter weather advisory will continue for the mountain areas overnight. Otherwise, much of the rest of the current forecast is on track. Temperatures will be a bit warmer on Tuesday, as the main area of low pressure pulls away from MT. Even warmer temperatures are expected by late in the work week. The air mass will still be unstable by the end of the week, so scattered showers/thunderstorms will be possible. Brusda && .AVIATION... 18/06Z TAF Period Widespread rain, a rain/snow mix, or snow will gradually exit eastern portions of Southwest through North Central Montana through 12-18z Tuesday; however, another disturbance pivoting southeast around the departing one will bring a return chance of showers and scattered thunderstorms moving from northwest to southeast across North Central and into portions of Southwest Montana beyond 12z Tuesday. IFR/MVFR/low-VFR conditions will prevail across all terminals regardless of falling precipitation, with the lowest and most persistent CIGS occurring in THE northerly upslope favored locations of Central and Southwest Montana. Mountain obscuration will continue across the entirety of the Norther Rockies over the next 24 hours. - Moldan Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 725 PM MDT Mon Jun 17 2024/ Key Points: -Rain and mountain snow continue through Tuesday morning with precipitation becoming showery during the day Tuesday -Showers and thunderstorms will develop most afternoons Wednesday through Friday as temperatures gradually warm Through Thursday Ongoing widespread rain and mountain snowfall continue across North Central and Southwestern Montana through the evening and overnight tonight as an anomalously cold weather system continues to work its way through the area. So far, most areas have seen a general .1-.2 inches of rainfall, though areas along a line from the Bears Paw Mountains to Great Falls to the Bob Marshall Wilderness Complex have seen amounts come in a bit higher, with up to .75 inches of precipitation in the past 24 hours, with some of that falling as snow above 6000 feet or so. Where snow has fallen, it appears that accumulations have generally been limited to grassy and elevated surfaces, and even there accumulations have generally been around an inch or two early this morning before daytime heating began to melt the snow faster than it fell after sunrise. We will have to watch for some accumulations after sunset again tonight, but this will come as the main area of precipitation begins to move off to the northeast, so any additional accumulations of snow will generally be a coating of up to 6 inches on the highest peaks. In the wake of this system tomorrow, upper level troughing and cold air aloft will linger across North Central and Southwestern Montana, which will help to spur the development of scattered to widespread showers and maybe a thunderstorm or two across the area. These showers and storms should bring a bit of additional moisture to many of us, with most areas seeing up to 0.1 inches of additional rainfall tomorrow. Temperatures will moderate a bit Wednesday and Thursday as our upper level flow becomes zonal/westerly, though we will have a few showers and thunderstorms develop each afternoon. Ludwig Thursday through Friday...ensemble clusters favor southwesterly flow aloft over the Northern Rockies as shortwave troughing moves from over the Eastern Pacific/Western Seaboard and towards the Northern and Central Rockies. This southwesterly flow regime will help to maintain scattered to numerous showers and storms, particularly over Central and North Central Montana, each day. Additionally, temperatures will moderate to near normal. Saturday through next Monday...quasi southwest to zonal flow is favored within the multi-model ensemble mean during the period, which is expected to translate to well above normal temperatures and isolated showers/storms each day across the Northern Rockies. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 39 58 37 67 / 80 80 40 30 CTB 35 53 32 65 / 40 80 30 30 HLN 42 64 40 72 / 90 70 40 20 BZN 33 59 33 69 / 90 60 30 20 WYS 28 52 24 63 / 90 60 20 10 DLN 33 56 32 65 / 80 30 20 10 HVR 42 61 40 69 / 80 70 40 30 LWT 34 54 34 65 / 100 80 40 40 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until noon MDT Tuesday for East Glacier Park Region-Southern Rocky Mountain Front. Winter Weather Advisory until 6 AM MDT Tuesday for Big Belt, Bridger and Castle Mountains-Elkhorn and Boulder Mountains- Gallatin and Madison County Mountains and Centennial Mountains- Little Belt and Highwood Mountains-Northwest Beaverhead County- Snowy and Judith Mountains. && $$ http://www.weather.gov/greatfalls