745 FXUS65 KTFX 100532 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1132 PM MDT Tue Oct 9 2018 Updated Aviation Discussion .SYNOPSIS... Snow continues tonight over the mountains of Western and Southwest Montana, with a mixture of rain and snow at lower elevations. Travel over mountain passes could be difficult with areas of fog and snow covered or icy roads. Precipitation ends for most areas by mid-day Wednesday, except snow will continue over the Southern Rocky Mountain Front. Temperatures will be well below average in the 30s to low 40s through Wednesday. && .UPDATE... Updated forecast is out. Main change was to increase pops mainly along/west of I-15. Good snowfall rates continue in the mountains this evening from northwest of Helena to west of Choteau. Snow falling around Helena, but roads seem pretty good in the Helena valley so held off on the advisory in the Helena valley, but did include it elsewhere in the county. Snowing fairly good over Kings Hill but seems fairly local in that area, so held off on expanding the advisory there. Otherwise, overall the snow should begin to slowly diminish after Midnight, but will likely take until late Wed afternoon before it diminishes completely. Overnight lows look on track, and with temperatures going well below freezing in many areas tonight, wet roadways/bridges will likely ice over by Wednesday morning. Brusda && .AVIATION... Updated 0600Z. Moist easterly flow continues across the region through much of the day on Wednesday, keeping low clouds in place across much of the area. Precipitation and lower visibility in snow is most widespread along the continental divide and adjacent areas through much of tonight with precipitation likely to diminish in coverage and intensity through the day on Wednesday. Hoenisch && .PREV DISCUSSION... /ISSUED 555 PM MDT Tue Oct 9 2018/ Tonight through Thursday...An early season snowfall continues tonight as a closed upper low tracks through western and southwest Montana. Easterly surface winds on the north side of the low are producing upslope snowfall over the Northern Rockies and adjacent Rocky Mountain Front. Snow and valley rain or rain/snow mix will expand across Southwest Montana tonight with the passing disturbance. Several inches of new snow are expected over mountain areas across the Southwest. The system is moving along quickly, so precipitation will end for most lower-elevation areas early Wednesday morning, while snow may linger over the mountains. Snow covered roads are likely over most of the mountain passes, and even at lower elevations wet road surfaces could freeze and create icy conditions for early Wednesday morning. A weak secondary wave organizes and passes through the region Wednesday night, creating chances for light rain or snow. The large scale upper level ridge finally shifts over western Montana on Thursday, yielding clearing skies and gradually warmer temperatures. Thursday night through Tuesday...Dry conditions are expected Thursday night into Friday morning as westerly downslope winds increase ahead of a Canadian cold front. The strengthening pressure gradient along the Northern and Southern Rocky Mountain Fronts Thursday night and into the day on Friday will likely lead to strong winds along the immediate east slopes of the Continental Divide and in wind favored areas, with gusts approaching 55 mph over this time frame. These westerly winds will also cause temperatures to warm within 10 degrees of normal across the CWA. 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 (with the exception of the Central Montana mountains Sunday morning, where some light precipitation is possible due to weak mid-level frontogenetical forcing). The latest forecast model runs continue to indicate that another shortwave trough may move through the area Monday into Monday night (especially impacting northeastern portions of the CWA). There is a lot of uncertainty in the strength/track of this disturbance, so have kept the probability for precipitation in 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/Moldan && .PRELIMINARY POINT TEMPS/POPS... GTF 29 40 27 43 / 100 10 10 10 CTB 26 34 24 41 / 100 50 20 10 HLN 32 41 30 44 / 100 20 20 20 BZN 30 40 26 42 / 60 10 20 20 WEY 23 40 24 40 / 70 30 60 40 DLN 27 38 25 42 / 100 20 20 20 HVR 30 41 28 44 / 30 0 10 10 LWT 28 35 26 39 / 60 20 20 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 6000 feet for Beaverhead. Winter Weather Advisory until 9 AM MDT Wednesday above 4000 feet for Broadwater. Winter Weather Advisory until 9 AM MDT Wednesday Jefferson. Winter Weather Advisory until 9 AM MDT Wednesday Central and Southern Lewis and Clark except the Helena valley is not in the advisory. && $$ http://www.weather.gov/greatfalls