110 FXUS65 KMSO 132203 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 303 PM MST SUN DEC 13 2015 ...Second round of snow tonight will heavily impact travel across portions of central Idaho and southwest Montana... .DISCUSSION... While today's winter storm has been mostly underwhelming for western Montana valleys from the Bitterroot to the Flathead, higher elevations and mountain passes have seen plenty of snow over the last 24 hours, with just shy of a foot reported at several locations. The valleys of MT which have missed out thus far have another shot at accumulating snow this afternoon and evening as a cold front sweeps through the area, ending the south winds which have dried out the lower atmosphere thus far today and prevented precipitation from reaching the ground in those areas. The focus of the storm now shifts to an area stretching from central Idaho to southwest Montana, where nearly a foot of snow is possible in some areas overnight. Valleys south of I-90 will pick up several inches as well, especially the upper reaches of the Clark Fork. In addition, the front pushing through tonight will cause winds to increase across southern Lemhi County ID and along the I-90 corridor from Deer Lodge eastward, leading to reduced visibilities. A winter storm warning continues for those areas. Another winter storm warning lingers for the mountains of west- central MT and central ID into tonight, as several more rounds of snow may impact travel in those areas. Elsewhere, advisories cover much of our area, with the exception of northwest MT which has likely seen most of its impactful snow already; only a few showers are expected overnight in that area. Colder air moving in tonight will lead to a colder day Monday, with most locations below freezing through the day. Wrap-around snow will continue to impact southwest Montana, especially areas near the Continental Divide. In addition, northerly flow and lingering moisture could lead to continued snow showers for the Camas Prairie of Idaho. Elsewhere, occasional snow showers are possible, but widespread impacts to travel are not expected. A northerly flow behind the exiting low pressure will keep light snow showers in the forecast for the day Tuesday, especially for areas east of Missoula and south of I-90. Only light additional snow accumulations are expected. Models continue to show a shortwave trough sliding through a northwesterly flow on Wednesday. Some models are trending the wave stronger each run, with a mid level low pressure moving over north- central Idaho. This type of weather pattern is historically very good for snow production in all valley locations of western Montana and central Idaho. How much snow is still in question, as models still differ on the placement of the heaviest precipitation. There is still an outside chance that this system continues to strengthen which could push the majority of the energy south of the area. Stay tuned to the forecast as we continue to iron out the details. Much cooler air will spill south out of Canada for the rest of the week. Low temperatures for western Montana will be in the low teens, with the highs struggling to get out of the 20s. North- central Idaho will also see below normal temperatures, with highs around the freezing mark. As we get to next weekend, another North Pacific system will impact the Northern Rockies. A warmer airmass will be associated with this system, that could setup an overrunning scenario. Long range forecast models differ with how much of a warm airmass will move in, and the location of where the boundary sets up. More details on this in the coming days. && .AVIATION... Snow will continue for north-central Idaho and southwest Montana this afternoon through Monday with persistent terrain obscurations. Northwest Montana could see isolated light showers linger through Monday, but minimal impact is expected. Snow showers in west-central Montana will decrease as well, as a cold front moves from northwest to southeast this evening. The cold front is expected to reach KMSO around 14/0000Z; light scattered snow showers with lower ceilings are then possible through around 14/04000Z. Looking at current model and satellite trends, the next round of moderate snowfall, low visibility, and low ceilings for KBTM and KSMN are forecast to be after 14/0400Z. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...Winter Storm Warning until 11 PM MST Monday Butte/Blackfoot Region. Winter Storm Warning until 11 AM MST Monday Bitterroot/Sapphire Mountains...Lower Clark Fork Region. Winter Weather Advisory until 11 AM MST Monday Missoula/Bitterroot Valleys. Winter Weather Advisory until 11 AM MST Monday Flathead/Mission Valleys. Winter Weather Advisory until 11 AM MST Monday Potomac/Seeley Lake Region...West Glacier Region. ID...Winter Storm Warning until 11 PM MST Monday Eastern Lemhi County. Winter Storm Warning until 11 AM MST /10 AM PST/ Monday Lower Hells Canyon/Salmon River Region...Northern Clearwater Mountains...Southern Clearwater Mountains...Western Lemhi County. Winter Weather Advisory until 10 AM PST Monday ABOVE 3000 FEET for the Orofino/Grangeville Region. && $$