881 FXUS65 KTFX 170415 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 915 PM MST Tue Dec 16 2014 .UPDATE... A band of light snow continues to push northward from Southwest Montana into Central Montana. However...as this band pushes northward...it is weakening a bit. Thus Bozeman...Helena...Great Falls and Lewistown look to be on the edges of this system and these locations will generally see just some minor snow accumulations. The heavier swath of around an inch of snowfall should move through the Dillon...Whitehall...Townsend and Kings Hill region. I have precip extending northward into the Havre area on Wednesday morning...but any snowfall in this region will be quite light...generally less than a quarter of an inch. In terms of fog...I have left the highlights alone...as patchy dense fog continues to affect portions of the region. The fog might not be as widespread in the Great Falls/Stanford areas right now...but just enough fog around to keep the highlight going for now. The Cut Bank area continues to have visibility around 1/4SM so the advisory looks good in this region. Overnight lows are on track...with just a few minor adjustments towards current readings. Brusda && .AVIATION... UPDATED 2350Z. Light snow continues to push northward into Southwest MT. Expect visibilities to generally be 1SM in areas of snow along with mountains obscured. The snow will spread into the Helena/Bozeman areas this evening...and then into the Great Falls/Lewistown areas over night. The snow should move into the Havre area on Wednesday morning. Areas of dense fog will continue to affect the Cut Bank area until Wednesday morning. Brusda && .PREV DISCUSSION... /ISSUED 450 PM MST Tue Dec 16 2014/ Tonight through Thursday...Relatively quiet conditions over central and north central Montana during the period. Areas of freezing fog continue to cover portions of north central Montana this afternoon...and those areas that did burn off will likely see the fog redevelop late this afternoon or this evening. Have extended the Freezing Fog Advisory for most of north central Montana until 11 a.m. Wednesday. Upper air pattern shows a high pressure ridge over the Rocky Mountain states with a low pressure trough over the west coast. Idiosyncrasies in the pattern are resulting in a split flow aloft over southwest and central Montana...and small weather systems embedded in the flow, and being steered into Montana, are being sheared apart and weakened. Best chance for snow from these systems will be over the southwest Montana mountains. Probabilities decrease to only slight chances as the system moves to the northeast over central Montana. As the high pressure ridge shifts east and the trough begins to move inland, another system will approach the area during the day Thursday. This again brings slight chances for snow mainly over the west and southwest mountains. Temperatures will remain near seasonal averages for this time of year. Thursday Night through Tuesday...A weak upper level ridge of high pressure will keep the forecast area mostly dry Thursday night and Friday. A shortwave trough will then move into the area Friday night into Saturday, bringing an increased chance of mountain snow. However, breezy westerly downslope winds will keep the plains dry. The weather pattern will change somewhat beginning on Sunday. An upper level ridge of high pressure will strengthen off the California coast and an upper level trough of low pressure will deepen from Hudson Bay into the Great Lakes. This will put Montana under the influence of a strong northwesterly flow aloft. The strongest winds aloft (60 to 70 kt at 700 mb) will occur Sunday into Monday with the passage of a disturbance embedded in the flow. This set- up will bring gusty westerly downslope winds to much of the area, but especially over the plains of north central Montana. In fact, some areas along the Rocky Mountain Front could approach High Wind criteria (40 mph sustained/58 mph gusts). Confidence is increasing that High Wind highlights may be needed for this event. There is also significant moisture with this disturbance, so have increased the chance for precipitation out onto the plains. Although the winds will decrease somewhat after the passage of the disturbance, the northwesterly flow aloft will remain fairly moist, so have kept the chance for precipitation above climatological normals across the area into Tuesday. The breezy winds throughout the period will keep temperatures around 10 degrees above normal. The warmest day of the period appears to be Monday, when most lower elevation locations should get well into the 40s. Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 17 37 25 37 / 50 30 10 10 CTB 18 34 22 36 / 10 10 10 10 HLN 23 31 18 33 / 80 20 10 20 BZN 18 31 14 30 / 90 20 10 20 WEY 21 31 17 28 / 100 40 20 30 DLN 22 33 17 33 / 100 20 10 20 HVR 17 31 19 35 / 0 30 20 10 LWT 14 38 22 39 / 60 40 10 10 && .TFX WATCHES/WARNINGS/ADVISORIES... FREEZING FOG ADVISORY until 11 AM MST Wednesday Cascade... Eastern Teton...Judith Basin...Southern Rocky Mountain Front. FREEZING FOG ADVISORY until 11 AM MST Wednesday Eastern Glacier...Eastern Pondera...Northern Rocky Mountain Front... Toole. && $$ weather.gov/greatfalls www.twitter.com/NWSGreatFalls www.facebook.com/NWSGreatFalls