FXUS65 KTFX 052120 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 220 PM MST Tue Mar 5 2024 .SYNOPSIS... The most active portion of weather over the upcoming week will be through Wednesday morning across Southwest Montana, where falling and blowing snow will be a concern near the Idaho border. Otherwise, expect a slow warming trend with mostly dry conditions through the weekend, though the warmer air will likely take a bit longer to arrive in cold prone valleys like the Milk River Valley. && .DISCUSSION... Through Wednesday morning... Embedded features within broad troughing will result in snow developing across Southwest Montana this afternoon and evening, primarily south of I-90. Dynamics aloft aren't overly impressive, though closer to the surface stronger 700 mb winds will result in both a concern for a band of snow developing via frontogenesis near the Idaho border, as well as blowing/drifting of snow in north south oriented valleys (Primarily the southern portions of the Madison River Valley) and over Idaho passes at and east of Monida Pass, through the evening. High resolution ensembles are highlighting now through about midnight as the most favorable time for the band of snow, but do not give more than around a 30% chance for inch per hour snowfall rates on major roadways away from West Yellowstone. The best opportunity for inch per hour snowfall rates will reside near West Yellowstone, where the probability is around 50% for the aforementioned timeframe. Winter Weather Advisories continue across areas near the Idaho border through early Wednesday morning, though most, if not all, impacts will be over by the time 5 AM rolls around Wednesday. Further north, the 12Z Raob from the office this morning shows a sharp inversion with temperatures rising to nearly 25 F at the top of the inversion around 800ft AGL. The challenge with this is determining how much warming will occur below the inversion at lower elevation locations across the plains. For example the Great Falls Airport warmed from near 10 degrees up into the mid 20's over ~ an hour late this morning. This type of warming should spread further out onto the plains this afternoon, but confidence that this will make it all the way north/east across the plains is low. Hence, I have kept temperatures across northeastern portions of the plains on the low side for the rest of today. A weak Canadian front drops south tonight, allowing for temperatures across most of the plains to fall into the single digits above/below zero. Wind chills along the Canadian border will likely approach -20 F in spots, but appears to be too localized to consider a wind chill advisory at this time. Wednesday into early next week... Upper level troughing begins to push off to the east Wednesday, but it will linger long enough to keep Wednesday on the cool side, with just a small chance for light snow across the eastern Hi-Line in the morning (Probability for a trace of snow is on the order of 40% in this area). Upper level ridging begins to build in off to the west Thursday, though a weak embedded disturbance will dive southeastward in the northwest flow aloft. Temperatures will begin to trend slightly upward, but not by much, especially in wind protected typical cold spots like the Milk River Valley. A more noticeable warming trend commences Friday, though again, locations prone to delayed warmups will likely hold onto colder temperatures a bit longer. Cluster guidance favors the ridge axis passing overhead sometime Saturday, which look to be the warmest day of the forecast period. Southwesterly flow aloft develops ahead of a building northeast Pacific trough as this ridge passes off to the east Sunday. Temperatures do not look to fall much as this transition takes place into early next week, but chances for precipitation, mainly in the mountains, will re-enter the forecast. -AM && .AVIATION... 1044 AM MST Tue Mar 5 2024 (05/18Z TAF Period) A disturbance emebedded within westerly flow aloft will continue to spread snow across SW MT this afternoon with periods of light snow and mainly MVFR conditions expected at KBZN but steadier snow and potential for IFR conditions exists at KEKS and especially areas to the south near the Idaho border. A few snow showers/flurries could make it as far north as KHLN and KLWT this afternoon, but mainly VFR conditions prevail otherwise. Lower ceilings and mountain obscuration persists through tonight across SW MT with some potential for fog development at KEKS and KBZN overnight if partial clearing occurs. Hoenisch Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 3 31 14 38 / 0 0 0 0 CTB -4 26 6 35 / 10 0 0 0 HLN 13 34 12 35 / 10 0 0 0 BZN 11 31 9 32 / 40 0 10 0 WYS 7 30 8 30 / 90 10 20 10 DLN 11 32 11 31 / 30 0 0 0 HVR 1 14 -2 24 / 40 20 0 0 LWT 8 28 10 34 / 20 0 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 AM MST Wednesday for Gallatin and Madison County Mountains and Centennial Mountains-Madison River Valley-Ruby Mountains and Southern Beaverhead Mountains. && $$ http://www.weather.gov/greatfalls