518 FXUS65 KTFX 082136 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 236 PM MST Tue Dec 8 2020 .SYNOPSIS... Winds will gradually decrease through the overnight hours tonight across Central and North Central Montana after a breezy to windy day. A fast moving disturbance will move across the Northern Rockies on Wednesday, bringing a return chance for mountain snow during the daylight hours. A cold front moving south from Canada during the late afternoon and through the overnight hours on Wednesday will then allow for snow to expand further east over the plains. && .DISCUSSION... Rest of today through tonight...primary concerns throughout the period will continue to be the on-going winds across Central and North Central Montana through early this evening. As of early this afternoon strong and gusty southwest winds continue to be experienced across portions of Central and North Central Montana, most notably in the Great Falls Area and along the Rocky Mountain. While the surface pressure gradient was weakening this morning and continued to weaken early this afternoon along the eastern slopes of the Rocky Mountain Front and northern slopes of the Central Montana mountains, winds have remained strong to at times very strong thanks to a nearly stationary mountain across the region. This stationary mountain wave, which has remained over the Great Falls Area since approximately 4:30am, has led to sustained winds of 35-45 mph and gusts as high as 61 mph at the Great Falls Airport through this afternoon. Thankfully, areas outside of the immediate Great Falls Area have seen wind speeds more along the lines of 25-35 mph, with gusts approaching 45-55 mph; therefore I will continue to hold-off on issuing a High Wind Warning for Cascade County as the winds appear to be rather localized, albeit over the main population core of Cascade County. Further to the northeast across Hill and Blaine Counties winds have so far remained below high wind criteria; and while the number of hours for peak mixing continues to decrease, the fact that H850 winds will remain within the 50-60kts range through 00z has me concerned that any mixing or mountain wave activity could very easily lead to high wind criteria speeds or gusts. Therefore I will continue to High Wind Warning for these two counties until 01z Wednesday for now. Decreasing winds through the overnight hours tonight allow temperatures to cool into the 30s and low 40s over Central and North Central Montana (versus the mid-40s to low 50s the night prior), with the teens and 20s expected in most valley locations of Southwest Montana (Yellowstone/Hebgen Valley will likely fall into the single digits above zero). Wednesday through Wednesday night...primary concern over the period will be the risk for accumulating snow in the mountains and even at some lower elevations (mainly over Central and North Central Montana). A broad Pacific trough crossing the Northern Rockies on Wednesday will usher in cooler and unsettled conditions to the region. High temperatures on Wednesday will cool into the 30s and 40s for most locations. Any snow/rain shower activity during the day on Wednesday is expected to be mostly along the Divide; however, a few isolated showers could sneak off of the mountains and over the plains/valleys. Guidance continues to show a surface low developing over North central Montana early Wednesday morning, before sliding southeast to Southeast Montana by Wednesday afternoon. As the surface low slides southeast Wednesday afternoon, a cold front will begin to push south across North Central Montana before stalling along the Central Montana mountains Wednesday night. This surface front, in addition to a mid-level front, should provide sufficient frontogenetic forcing for additional precipitation to develop over the plains of Central and North Central Montana late Wednesday afternoon and through the overnight hours. This type of set up usually favors the northern upslope regions of the Central Montana mountains and locations in between Great Falls and Lewistown. Snowfall amounts will likely be on the light side in these areas and not exceed 1 inch; however, some isolated locations could approach 3 inches. This situation will be monitored for the need of winter weather products should confidence in higher amounts increase. Further to the northwest along the Northern Rocky Mountain Front snowfall amounts of 1 to 2 inches are expected at lower elevations, with 2 to 5 inches over Marias Pass. Given the higher confidence in snowfall amounts over the Northern Rocky Mountain Font, will issue a Winter Weather Advisory for the period from 12z Wednesday through 06z Thursday to cover the potential impacts to travel, especially Wednesday afternoon through early Wednesday evening. - Moldan/RCG Thursday through next Tuesday...Temperatures will rebound back to the 30s and lower 40s on Thursday as a shortwave ridge of high pressure moves in and partial clearing takes place. Teens and 20s can be expected for low temperatures once again Thursday night, though the cooler southwest valleys may dip into the single digits above and below zero. General anticyclonic flow continues on Friday, providing more seasonable temperatures and mostly dry conditions. Still a few mountain snow showers can't be ruled out, especially over the southwest. There is some uncertainty for the weekend into early next week but it appears that the unsettled pattern will continue along with slightly above normal temperatures. RCG && .AVIATION... 1114 AM MST Tue Dec 8 2020 (08/18Z TAF period) No change from the previous discussion. Primarily VFR conditions over the next 24 hours across the region, though there will be an abundance of high and mid-level cloudiness for much of the period. Areas along the Northern Divide will likely observe a period of mountain obscuration this afternoon as some snow showers move into the area. Gusty southwesterly surface winds can be expected and may gust gusts up to 45 kts over the plains. Stronger and more westerly winds aloft may result in periods of LLWS for the plains terminals, especially during times of lighter surface winds. Expect widespread turbulence and mountain wave activity through this evening. Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 42 50 25 38 / 20 20 40 0 CTB 33 42 22 34 / 30 40 30 0 HLN 28 44 24 37 / 0 10 20 0 BZN 20 45 19 35 / 0 10 20 0 WYS 2 30 4 24 / 0 10 10 0 DLN 22 43 16 30 / 0 10 10 0 HVR 31 42 24 35 / 20 30 30 0 LWT 35 51 23 35 / 10 20 30 0 && .TFX WATCHES/WARNINGS/ADVISORIES... High Wind Warning until 5 PM MST this afternoon Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky Mountain Front. High Wind Warning until 6 PM MST this evening Blaine...Hill. && $$ http://www.weather.gov/greatfalls