WEATHER DISCUSSION: Bitterly cold, arctic air has settled into central and eastern Montana. A reinforcing shot of even colder, arctic air arrives on Wednesday as highs struggle to exceed -20 in parts of central Montana on Wednesday. Lowest maximum temperature and minimum temperature records will be challenged through Friday. Some areas may see the first -40s in decades by Wednesday night. Frostbite will form on exposed skin in as little as 5-10 minutes as wind chills will be in the -40s and -50s.
A high impact winter storm impacts the region Tuesday and Wednesday. Although accumulations should remain light to moderate for most areas, the snow coupled with subzero temperatures and gusty winds (up to 40mph) will create treacherous travel region-wide. Models indicate 0.1-0.25" of liquid (up to 0.5" in higher elevations), which translates to 2-5" of snow accumulation given the high snow ratios expected in the cold temperatures. Higher elevations and locations near I-90 have the greatest potential for over 6" of snow accumulation.
The snow winds down Wednesday morning as an arctic high builds into the region, directly over central Montana. Mostly sunny skies and continued dangerous wind chills are expected on Thursday. A southwest breeze increases Thursday night creating blowing and drifting snow for the Rocky Mountain Front. Temperatures begin to moderate, but it is a slow process. Valley locations will be the last to warm up.
Temperatures should reach climatological averages by Saturday afternoon in central Montana, likely not until Christmas Day or even Monday for eastern Montana. Inversions will continue to cause colder temperatures in valleys. Overall, pre-Christmas travel looks fairly quiet. Rain and snow showers are possible on Christmas Eve and Christmas Day. The main concern is going to be blowing and drifting snow as it is going to be very breezy throughout the weekend.
MONDAY NIGHT: Mostly cloudy. A northerly breeze sustained at 3-7 MPH. Temperatures falling into the -10s and -20s, wind chills in the -30s and -40s.
TUESDAY: Snow developing during the morning. A north-northeasterly breeze sustained at 5-10 MPH. Highs in the low to mid -10s for central Montana, -0s for the Helena area. Wind chills as low as -45. Steady snow overnight as temperatures fall into the -20s. 2-4 inches of accumulation for north central and eastern Montana. 4-8" for the Helena area and the I-90 corridor from Missoula to Bozeman. 6"+ for higher elevations of central Montana and areas along the Continental Divide. A north-northwesterly breeze sustained at 5-15 MPH throughout the night, gusting at times to 35 MPH. Wind chills as low as -50.
WEDNESDAY: Snow tapering, mostly cloudy. Highs in the -10s and lower -20s. Dangerous wind chills as low as -55. Mostly cloudy overnight as temperatures fall into the -30s and -40s. A sustained NW breeze of 5-15 MPH will create wind chills in the -50s to around -60.
THURSDAY: Mostly sunny and frigid. Wind gradually shifting to the westerly direction, sustained at 5-10 MPH. Temperatures starting in the -20s and -30s rising into the -10s by the evening. Wind chills as low as -60. Temperatures will continue to climb overnight.
FRIDAY: Mostly cloudy. Slight chance of a snow shower. Temperatures climbing into the 0s by the evening. Wind chills remain subzero. Remaining mostly cloudy overnight as temperatures fall into the -0s and 0s in central Montana, -10s and -20s for the Hi-Line and eastern Montana.
CHRISTMAS EVE: Mostly cloudy and breezy. Blowing snow likely. Scattered rain and snow showers. High temperatures in the mid 30s for central Montana. 0s and 10s for eastern Montana and valley locations. Scattered snow showers overnight as temperatures fall into the 20s in central Montana, -0s and 0s for eastern Montana.
CHRISTMAS DAY: Mostly cloudy, milder and scattered rain or snow showers. Highs in the upper 30s and lower 40s, 20s for far eastern Montana. Remaining mostly cloudy overnight as temperatures fall into the low to mid 20s, with 10s for eastern Montana.
MONDAY: Mostly cloudy. Highs in the low to mid 40s for central Montana. 20s and 30s for the Hi-Line.