177 FXUS65 KTFX 140509 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1109 PM MDT Sun Apr 13 2025 Aviation Section Updated. .KEY MESSAGES... - Gusty winds diminish through the afternoon and early evening today. - Trending warmer and dry through Tuesday. - Transitioning to cooler and wetter for Wednesday evening into Thursday, with large uncertainty in precipitation amounts and potential impacts. && .UPDATE... /Issued 817 PM MDT Sun Apr 13 2025/ 8:15 PM MDT : Skies are clearing quickly, and winds subsiding, from west to east this evening, with these conditions promoting ideal conditions for radiational cooling overnight tonight. Have thus lowered temperatures by 2-4 degrees from the on-going forecast to account for these ideal conditions. Otherwise the remainder of the forecast remains on track. Still some concerns for fog developing in the valleys of Southwest and Central Montana where recent precipitation has fallen over the past 12-24 hours, but with BUFKIT soundings still supporting a very dry boundary layer overnight I have kept any mention of fog out at this time. Surface observations within these valleys in Southwest and Central Montana currently have dewpoint depressions of 20 to nearly 40 degrees, which helps to support the aforementioned BUFKIT soundings. None-the-less, would not be surprised if a few localized areas (especially near water sources and where recent precipitation has fallen) see patchy fog through Monday morning. - Moldan 6:45 PM MDT : Early evening update has been published; which resulted in the addition of low end (i.e. 15%) PoPs for areas along and northeast of a line from Judith Gap, to Great Falls, to Marias Pass where scattered radar returns have been persistent so far early this evening. - Moldan && .DISCUSSION... /Issued 817 PM MDT Sun Apr 13 2025/ - Meteorological Overview: Upper level troughing over eastern MT and the Dakotas is quickly exiting eastward this afternoon, allowing for upper level ridging to begin building in. At the surface, low pressure across ND is also exiting eastward, which has allowed for precipitation to largely diminish. Strong mid level northwesterly flow behind this surface low is quickly diminishing, which was the source for strong wind gusts in Fergus county and vicinity this morning and early afternoon. Given this opportunity for strong winds has subsided, the High Wind Warning has been canceled. Largely benign conditions will build in tonight as skies clear and winds further diminish. Recent precipitation combined with light winds and clear skies may promote some fog formation toward sunrise tomorrow, but forecast soundings aren`t too enthused with these prospects. For this reason I have withheld mention of fog at this time. Other than that, Monday and Tuesday are looking pleasant, with temperatures near or a touch above average Monday and above average on Tuesday. Heading into Wednesday flow aloft begins to become more zonal as troughing from BC begins sliding southward toward WA/OR/ID. This troughing slows and becomes a closed upper low at some point Wednesday evening or night across the aforementioned states. There is general agreement for this system to continue sliding southward toward CA/NV and vicinity toward Thursday and Friday. The track of this system will bring colder air into the region behind a Canadian cold front Wednesday afternoon or evening, with a period of snow likely to develop in tandem. Ahead of this front there looks to be enough instability for showers or perhaps a few thunderstorms, mostly across Southwest Montana Wednesday afternoon. There is quite a bit of uncertainty with this system, but at least some lower elevation snow is appearing likely Wednesday afternoon/evening through Thursday. Additional concerns and a discussion on scenarios/uncertainty is included below in the forecast confidence and uncertainty section. Heading toward Friday and Saturday, clusters are in relatively good agreement that brief, weak ridging will attempt to build in across the region promoting a trend toward drier and warmer conditions again. By Sunday confidence becomes much lower in the evolution of the pattern, with low-end opportunities for precipitation creeping back into the forecast. -AM - Forecast Confidence & Scenarios: The range of scenarios for the Wednesday/Thursday timeframe is quite large. The more aggressive scenario portrayed by the GFS, holds on to the upper disturbance in the WA/OR/ID area longer than other guidance. This would result in a longer duration window for snow at all elevations, with wind becoming a greater concern. This more aggressive scenario features a barrier jet along the Rocky Mountain Front, which would raise concerns for blowing snow in addition to falling snow for this area. Guidance that is quicker to send the upper disturbance southward towards CA/NV results in a more narrow window for snow, and as a result has much lower precipitation amounts. These quicker scenarios also feature less of a wind concern at lower elevations. To put into perspective the spread of potential outcomes, the difference between 10th percentile snow amounts (Reasonable low-end amount) and 90th percentile (Reasonable high-end amount) is greater than 5 inches for Cut Bank, Great Falls, Lewistown, Helena and Bozeman, among other locations. That spread between low and high-end amounts increases to around a foot or more over passes such as Marias Pass, Rogers Pass, and Kings Hill Pass. The takeaway at this point is for at least a period of cooler weather and mountain snow Wednesday PM into Thursday, with higher end scenarios including heavy mountain snow and impactful lower elevation snow and wind as well. -AM && .AVIATION... 14/06Z TAF Period VFR condtions will prevail at all terminals during the duration of this TAF period. There will be light winds with few high-level clouds around for the most part due to an upper-level ridge building in over North-central, Central, and Southwestern Montana. -IG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 26 60 37 71 / 10 10 0 0 CTB 25 58 32 67 / 20 10 0 0 HLN 27 61 36 72 / 10 0 0 0 BZN 20 57 30 70 / 10 0 0 0 WYS 9 54 19 62 / 10 0 0 0 DLN 23 60 33 70 / 10 0 0 0 HVR 25 58 30 74 / 20 20 0 0 LWT 23 52 33 68 / 10 10 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls