619 FXUS65 KMSO 060046 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 546 PM MST Tue Feb 5 2019 .UPDATE...A low pressure system currently located on the Oregon and Idaho border, will track off to the east overnight, clipping Southwest Montana. It has brought in light snow for Lost Trail Pass, Lemhi County, and the Bitterroot Valley. Conditions in the Bitterroot have quickly deteriorated to snow covered and slick roads, with reduced visibility. Therefore, we have added a winter weather advisory through Wednesday morning. Light snow will spread further north through the evening. As the low passes off to our east around midnight, intensities will decrease, although light snow is expected to persist for at least Central and Southwest Montana through late afternoon Wednesday. && .AVIATION... Low clouds and widespread light snow will be present over Northern Rockies air space for much of the next 24 hours. KSMN and KBTM are the terminals that will be most impacted, with long-lived low ceilings and visibility due to snow. Conditions at KSMN and KBTM will slowly improve after 06/1200Z. Though less long lived, KMSO and KGPI will also see periods of lowered ceiling and visibility due to light snow through the night. Elsewhere across the region, terrain obscurations will be common. && .PREV DISCUSSION... /ISSUED 243 PM MST Tue Feb 5 2019/ DISCUSSION... Light snow and very cold wind chill will return to the Northern Rockies this evening through Wednesday. Pacific moisture streaming up from the southwest will move over Lemhi County Idaho and southwest Montana, producing snow accumulations in the 2 to 5 inch range for valleys and 6 to 8 inch range for Lost Trail and Bannock Passes. Other areas across the region will also see snow accumulations up to 2 inches. Prepare for snow covered roadways and allow extra travel time. Wind chill temperatures down to minus 30 degrees will exist near the Continental Divide and will also be evident within terrain gaps (such as Badrock Canyon on Highway 2 east of Kalispell). Snow and wind will diminish gradually through Wednesday, with temperatures remaining well below the seasonal average. A relatively dry scenario will develop over the Northern Rockies on Thursday, however clouds and cold temperatures will remain in place ahead of the next storm system soon to follow. The active winter pattern will be returning to the Northern Rockies by the end of the day on Friday, and remaining active and cold through the weekend. A resurgence of cold Canadian arctic air will again spill across western Montana sometime during the day Friday and/or early Saturday. At the same time, a moist Pacific airmass is expected to overrun the arctic airmass. This looks similar to what we just experienced this past weekend. Some differences, in terms of available moisture and the strength of the arctic winds look to be there with this one though. We do see less moisture, and not as strong of wind. But expect widespread valley and mountain snow, as well as cold east-northeast winds producing dangerous wind chills, especially along the Continental Divide. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...Winter Weather Advisory until 11 AM MST Wednesday Bitterroot/Sapphire Mountains...Butte/Blackfoot Region. Wind Chill Advisory from 11 PM this evening to 10 AM MST Wednesday Flathead/Mission Valleys...West Glacier Region. Winter Weather Advisory until 11 AM MST Wednesday Missoula/Bitterroot Valleys. ID...Winter Weather Advisory until 11 AM MST Wednesday Eastern Lemhi County...Western Lemhi County. && $$