111 FXUS65 KTFX 301638 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 938 AM MST Sat Nov 30 2019 .UPDATE... We have cancelled the Winter Weather Advisory for our northwestern areas. With increasing cross-barrier winds expected to develop as early as this evening across the immediate Rocky Mountain Front, we have issued a Blizzard Warning for expected ground blizzard conditions developing. Those conditions are expected to become even more widespread across the Northern Rocky Mountain Front as winds increase further Sunday night through Monday, with significant impacts and disruptions to everyday tasks/routines very likely to be impacted. For the Southern Rocky Mountain Front and eastern Glacier County, there is a bit more uncertainty in the development of ground blizzard conditions, but at the very least expectations are that there will be significant blowing and drifting of snow. For this reason, a Winter Storm Watch for potential ground blizzard conditions has been issued beginning Sunday evening and lasting through Monday night. As strong winds move off of the Rocky Mountain Front and out onto the adjacent plains, including the Interstate 15 and US Highways 87 and 2 corridors, blowing and drifting snow is likely to become a concern especially late Sunday night through Monday. We will continue to assess the need for winter weather highlights to the east leading up to that time. && .SYNOPSIS... Light snow over the region will diminish from the west this morning, and skies should become partly cloudy during the afternoon. However, this could cause patchy fog to form overnight. Temperatures will remain well below normal, but a slight increasing in westerly winds on Sunday should help warm temperatures closer to normal. Breezy winds Monday into Tuesday will help keep the area dry, as temperatures warm to above normal, but these increasing winds could cause areas of blowing snow. && .AVIATION... Updated 445 AM MST Sat Nov 30 2019 (30/12Z TAF Period) The winter storm over the region will continue to move east out of the area through 17Z, causing the widespread low MVFR/IFR conditions with mountain obscuration in snow, fog, and low clouds to decrease from the west. Weak high pressure will start to build into the area after 17Z, causing conditions to improve to mostly VFR as skies gradually clear through 00Z. Although the clearing skies will likely cause patchy mainly valley fog to develop after 03Z, confidence in exact locations and density of this fog is low, so will keep mention out of the TAFs at this time. Coulston && .PREV DISCUSSION... /ISSUED 445 AM MST Sat Nov 30 2019/ Today through Sunday... The low pressure system responsible for the snow the last couple of days is over the central Great Plains as of early this morning. It seems to be taking more of an easterly track than previously expected, which is likely why the snow is decreasing a bit quicker than previously expected. The snow is still fairly widespread across North Central and Southwest Montana, but the heavy snow is currently limited to the Little Belt Mountains and east into the Lewistown area. The snow should continue decreasing throughout the morning, yielding mostly an additional inch or two. Will therefore continue the Winter Warnings and Advisories as is through the morning and possibly cancel areas early where the snow ends. Otherwise, weak high pressure aloft gradually builds into the forecast area this afternoon, tonight, and into Sunday between the Great Plains system and a low pressure area along the Pacific Northwest coast. This will help bring clearing skies to the area during this time, which should cause at least patchy fog to develop overnight in the southwest valleys and over the eastern plains (including the Havre and Lewistown areas). Light to breezy westerly surface winds will develop over the east slopes of the Rockies throughout the weekend, which will hinder fog development there, but it may be enough wind close to the Rocky Mountain Front to cause areas of blowing snow. The cold airmass will remain in place through tonight, keeping temperatures 15 to 20 degrees below normal, but the clearing skies and wind development should help warm temperatures closer to normal for Sunday. Coulston Sunday Night through next Saturday... A weakening shortwave disturbance in westerly flow aloft moves across the region Sunday night through Monday morning, bringing a chance of mainly mountain snow showers. More importantly, winds aloft and surface pressure gradient across the Rockies look to peak Monday morning with the passage of this system and gusts to over 50 mph are a possibility along the Rocky Mtn Front and areas immediately east with gusts to 30-40 mph further east across the plains of north-central MT. Windy, but mainly dry conditions persist through Wednesday, keeping temperatures somewhat above seasonal averages for early December. Greatest temperature departures from average will be across north-central MT with daytime temperatures potentially warming well into the 40s if/where snow can be melted/scoured by winds. Warming will be more subdued across SW MT valleys where winds will be lighter. A weather disturbance moving along the US/Canadian border late Wednesday and Thursday looks to push a relatively weak Canadian cold front through the area, cooling temperatures some as well as bringing a chance for some light snow showers. Temperatures look to rebound fairly quickly however as ridging rebuilds Friday and Saturday ahead of the next more organized upper level through moving onto the west coast next weekend. Hoenisch && .PRELIMINARY POINT TEMPS/POPS... GTF 18 9 32 25 / 70 0 0 10 CTB 17 8 32 24 / 30 0 0 10 HLN 20 4 30 16 / 60 0 0 10 BZN 21 1 31 15 / 70 0 0 10 WEY 20 -2 26 11 / 60 10 0 20 DLN 22 3 28 16 / 60 0 10 10 HVR 19 3 27 17 / 80 10 0 10 LWT 17 3 34 23 / 90 10 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 11 AM MST this morning Beaverhead...Broadwater...Jefferson...Madison. Winter Storm Warning until 11 AM MST this morning Blaine... Cascade...Chouteau...Fergus...Gallatin...Hill...Judith Basin... Meagher. Winter Storm Watch from Sunday evening through late Monday night Eastern Glacier...Southern Rocky Mountain Front. Blizzard Warning from 9 PM this evening to 6 AM MST Tuesday Northern Rocky Mountain Front. && $$ http://www.weather.gov/greatfalls