FXUS65 KTFX 290148 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 748 PM MDT Wed Aug 28 2024 UPDATED AVIATION SECTION .SYNOPSIS... Rain and snow will continue to affect North Central MT through tonight. On Thursday, expect some morning showers over North Central, while drier and warmer air will start to move northward into Southwest MT. By this weekend, expect warm afternoon temperatures across all of North Central and Southwest MT, with dry conditions expected through Labor Day. && .UPDATE... 6 PM evening update...Updated forecast to remove high wind warning. The winter weather advisory for the Northern Rockies was extended until Midnight. Also increased Pops over North Central MT, where light rain continues to fall. Brisk winds will continue over much of the CWA through this evening. Brusda && .AVIATION... 29/00Z TAF Period Moisture wrapping around a low pressure system will bring widespread mountain-obscuring rain showers and mountain snow showers with low VFR/MVFR conditions to much of North Central (KCTB, KHVR) and Central (KGTF, KLWT, KHLN) Montana through around 12Z. Mainly high- and mid-level cloudiness will keep conditions VFR for Southwest Montana (KBZN, KEKS, KWYS). Clouds and precipitation should move east out of the area with the system starting around 08Z and continuing through around 15Z, leaving skies mostly clear through the remainder of the period. Winds will also be a concern through the period, as west to northwest winds of 15 to 20 kt will be common with gusts up to 40 kt at times, possibly causing some mountain wave turbulence and low level wind shear. Note: The observations from KCTB, KHLN, and KHVR are not readily available, so have included AMD NOT SKED in those TAFs until the communication issue is resolved. Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 450 PM MDT Wed Aug 28 2024/ Today through Thursday...Accumulating snow will continue for the higher elevations along the Rocky Mountain Front through the rest of the evening. Additional accumulations of less than 4 inches are expected at the highest peaks. Otherwise, breezy conditions will continue through the rest of the evening and through the overnight hours with widespread gusts up to 40 mph possible for north-central Montana. -thor A potent H500 longwave trough, with heights that are 1.5 to 2.5 standard deviations below normal or near the 2.5th to 10th percentile of climatology, will continue slide east and over the Northern Rockies through Thursday. At the surface an associated Pacific cold front has now pushed east and across most of Southwest through North Central Montana, with strong cold air advection in wake of the front helping to support strong and gusty west to northwest winds and temperature falls into the upper 30s to 40s. Several areas along the Rocky Mountain Front and Hi-Line out to Blaine County have already reached High Wind criteria between the late evening hours on Tuesday through early this morning with the initial frontal surge, with the focus of strongest winds through the remainder of the day today being focused to the Rocky Mountain Front and immediate eastern plains out to the I-15 corridor where EFI values range from 0.8 to 0.9 amongst a shift of tails of 1. These areas are also supported by the highest NBM probabilities for wind gusts in excess of 48kts, with a 40-70% chance of exceeding 48kts here. Continued strong cold air advection over the remainder of the plains of Central and North Central Montana through tonight will help to support wind gusts of between 35-45kts, but a few isolated instance of higher wind gusts can't be ruled out given a 20-40% chance of wind gusts exceeding 48kts. Given the aforementioned probabilities we will continue the High Wind Warning for The Rocky Mountain Front and adjacent foothills and plains, Eastern Glacier, Western Toole, and Central Pondera Counties, and Eastern Toole and Liberty Counties , but forgo expanding any further east (due to lower probabilities). In addition to the strong winds, recent deterministic and ensemble guidance have honed in on the potential for impactful snow accumulations above 5000 feet in the mountains of Glacier National Park from this morning through the evening hours tonight, especially from the mid-morning through early afternoon hours. Latest probabilities for Logan Pass suggest an 85% chance for snow accumulations of 4" or more, with a 25% chance for 6" or more. This shift to impactful snow accumulations, which began 12-24 hours ago and remains in both ensemble and deterministic guidance, has prompted the issuance of a Winter Weather Advisory for the East Glacier Park Region due to the expected impacts to travel on roads in Glacier National Park and backcountry recreation. Here slushy and slippery conditions on roadways above 5000 feet are expected; with backcountry trails, especially over mountain passes, becoming snow covered and slippery. Strong winds will also combine with the falling snow and lead to periods of limited visibility. Backcountry users of Glacier National Park should be prepared for winter conditions, which could make trail conditions hazardous. Overall dry conditions are then expected through the day on Thursday as the H500 trough slides east and over the Northern High Plains, with breezy (but decreasing) west to northwest winds. High temperatures today will be well below normal and in the 50s to near 70 degrees across lower elevations (30s to 40s in the mountains), with readings rebounding on Thursday back unto the mid-60s to mid- 70s across lower elevations. Friday through next Wednesday...ensemble clusters strongly favor overall ridging over the Northern Rockies through the period; however, beyond Sunday the upper level flow will become increasingly southwesterly as the ridge axis shifts east of the region. This transition to southwesterly flow aloft combined with weak disturbance lifting northeast within the flow will bring increasing chances for isolated to scattered showers and thunderstorms to Southwest through North Central Montana through the first half of the upcoming work week. Temperatures will fluctuate throughout the entire period from times of near normal to above/well above normal. - Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 49 77 46 88 / 90 10 0 0 CTB 44 74 44 83 / 80 0 0 0 HLN 47 79 48 89 / 20 0 0 0 BZN 39 76 42 87 / 10 0 0 0 WYS 28 69 31 78 / 0 0 0 0 DLN 35 73 40 83 / 0 0 0 0 HVR 47 75 47 85 / 80 10 0 0 LWT 46 71 46 85 / 50 10 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until midnight MDT tonight for East Glacier Park Region. && $$ http://www.weather.gov/greatfalls