507 FXUS65 KTFX 091749 AAC AFDTFX Area Forecast Discussion...UPDATED National Weather Service Great Falls MT 914 AM MDT Tue Oct 9 2018 Aviation Section Updated. .UPDATE... Web Cam and surface observations indicate snow levels are lower than the existing winter weather advisories cover. Therefore, the winter weather advisories have been expanded to include lower elevations, but still exclude most major cities where roads should remain wet even through snowfall. We will continue to monitor for potential impacts from snow and ice that could develop overnight. .PREV UPDATE... /ISSUED 914 AM MDT Tue Oct 9 2018/ Updated current conditions to reflect areas of fog over the western portions of North-Central Montana. Increasing chances of PoPs mainly over Central and South-West Montana as an upper level low continues to track across south-West Montana. Otherwise the forecast remains on track and minimal changes were needed. && .SYNOPSIS... A cold storm system moving southeast through Idaho today and tonight will bring snow to the mountains of western and southwest Montana with a mixture of rain and snow at lower elevations. Travel over mountain passes along the continental divide could be difficult tonight as temperatures drop below freezing and road surfaces become snow covered and slick. Little or no snow accumulation is expected across the lower elevations however temperatures will be well below average in the 30s to low 40s through Wednesday. && .AVIATION... Updated 1740Z. Cold and moist storm system tracks SE across the Northern Rockies today and tonight with moist SE to E flow aloft circulating across the region. Precipitation increases across western portions of north- central and SW MT with widespread snow and low ceilings over the continental divide through tonight. Though widespread precipitation will be focused along and adjacent to the continental divide, occasional light precipitation, low clouds and potential for areas fog/drizzle will persist across many areas further east though tonight. && .PREV DISCUSSION... /ISSUED 530 AM MDT Tue Oct 9 2018/ Today through Wednesday...A fairly potent upper level wave and jet streak currently moving from BC south into WA and ID this morning will continue southeast through ID today, pivoting across UT and WY tonight. Rain and snow developed overnight along the east slopes of the Rockies and western plains of N-central MT thanks to moist easterly upslope flow to the east of the mid level circulation and precipitation will continue along the Rocky Mtn Front and immediate east slopes through today and tonight before diminishing Wednesday. Precipitation currently observed across northern ID and eastern WA more directly associated with the upper level wave will shift southeast today with rain and snow developing over western portions of central and SW MT later this morning and continuing through this evening before diminishing to showers on Wednesday. Main impacts with this system continue to look to be focused along the continental divide and adjacent areas including the immediate east slope areas along the Rocky Mtn Front and a Winter Weather Advisory will be issued to highlight potential difficult travel over mtn passes in these areas. Through this afternoon it is likely that road surfaces will remain warm enough to prevent snow accumulation with greater impacts to travel over Mtn passes likely this evening as road surface temperatures dip, allowing for wet and/or slushy conditions to freeze up with additional light snow accumulations occurring overnight as well. Snow levels currently ranging from around 3000 feet in the north to around 6000 feet in the south will fluctuate some through today before further lowering tonight. Moist and cyclonic flow aloft lingers over the Northern Rockies and MT behind the exiting upper level wave through Wednesday night with some showers continuing, primarily across the mountains of western and SW MT. Hoenisch Thursday through Tuesday...Lingering light snow over southwest Montana will diminish during the day on Thursday as the low pressure trough exits the area to the southeast. Dry conditions are expected Thursday night into Friday morning as westerly downslope winds increase ahead of a Canadian cold front. This will also cause temperatures to warm within 10 degrees of normal. However, the shortwave trough in the northwest flow will strengthen as it moves south into the Montana/Wyoming/Dakotas area Friday afternoon into Friday night. This strengthening and movement a bit farther west will bring a better chance for precipitation than originally thought, as well as much cooler temperatures. Have therefore increased PoPs into the likely category in the favored upslope areas of the east slopes of the Rockies on Friday night. This low pressure trough will be slow to exit the area to the east, so have kept a chance of precipitation through the day on Saturday. The high pressure ridge off the Pacific coast will then gradually move east to the coast itself Sunday through Tuesday. Sunday and Sunday night will be dry between systems, but this latest forecast model run indicates that another shortwave trough may move through the area Monday into Monday night. There is a lot of uncertainty in the strength of this disturbance, so have increased the probability for precipitation into the slight chance to chance range and will re- evaluate adjust as necessary over the next couple of days. Temperatures will warm back closer to normal again for Monday and Tuesday. Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 42 29 40 25 / 30 30 20 20 CTB 36 27 35 22 / 60 40 40 10 HLN 42 32 41 29 / 60 50 20 30 BZN 42 29 41 24 / 40 30 20 20 WEY 39 23 41 24 / 70 70 40 50 DLN 40 27 38 24 / 80 80 30 30 HVR 43 30 42 26 / 10 10 10 10 LWT 37 27 35 25 / 30 50 30 20 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 9 AM MDT Wednesday Northern Rocky Mountain Front...Southern Rocky Mountain Front. Winter Weather Advisory until 9 AM MDT Wednesday above 4000 feet for Broadwater...Central and Southern Lewis and Clark... Jefferson. Winter Weather Advisory until 9 AM MDT Wednesday above 6000 feet for Beaverhead. && $$ http://www.weather.gov/greatfalls