FXUS65 KTFX 051744 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1044 AM MST Tue Mar 5 2024 Updated Aviation Discussion .SYNOPSIS... Snowfall returns to Southwestern Montana today as a fast moving weather system moves across the Snake River Valley. Further north, expect temperatures to moderate a bit with most areas seeing temperatures in the mid 20s to mid 30s. Beyond tomorrow, expect temperatures to warm up across the area through the end of the week. && .UPDATE... Embedded features within broad troughing will result in snow developing across Southwest Montana today, 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. High resolution ensembles are highlighting the ~2 PM to midnight timeframe this afternoon/evening as the most favorable 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. 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. Surface observations above 4200 ft or so are already in the 20s F, demonstrating this inversion may be even more shallow in spots across the plains. This will be the challenge at lower elevations on the plains today, determining how much of this inversion is eroded away and thus what the forecast high temperatures will be. I have opted to be more on the optimistic side (Higher temperatures) closer to terrain, but favored a blend down across the plains, largely east of I-15 and north of MT-200. -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. && .PREV DISCUSSION... /ISSUED 521 AM MST Tue Mar 5 2024/ A low pressure system will move through southern Montana today bringing snow to area now through tomorrow morning. Snow totals in southwestern Montana, compared to the last forecast, decreased slightly with accumulations still more than enough to justify an advisory but not enough to upgrade to a warning. That being said, there is still a concern for both snow bands developing and blowing snow this afternoon as winds will be gusting up to 40 mph at times. Should these two come together with a greater force than what is currently forecasted, the advisory will need to be upgraded. Snow showers will taper off overnight and end by late Wednesday morning. Behind this system, temperatures will warm up as a ridge starts to build over the western CONUS with weekend temperatures in the 40s and 50s across lower elevations. Heading into early next week, long range models continue to point towards the ridge breaking down which will bring unsettled weather back to the region. However the specifics remain uncertain at this time. -thor && .PRELIMINARY POINT TEMPS/POPS... GTF 34 12 34 14 / 0 0 0 0 CTB 25 3 27 7 / 0 10 0 0 HLN 33 13 35 12 / 10 10 0 0 BZN 30 11 32 9 / 50 40 0 0 WYS 28 7 29 7 / 90 90 30 10 DLN 30 11 32 10 / 50 30 0 0 HVR 15 1 23 4 / 0 30 10 0 LWT 31 11 28 11 / 20 20 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