WEATHER DISCUSSION: Dangerous cold will persist for most of the upcoming week. The worst of the extreme cold is going to be Wednesday and Thursday, where wind chills will be as low as the -40s and -50s at times. Although, temperatures and wind chills remain dangerous throughout the entire week. Temperatures likely do not rise above 0 until Friday for central Montana and Saturday or Sunday for eastern Montana. Frostbite can form in as little as 10 minutes in these kind of wind chills. Prepare yourself, your family and your pets or livestock for these very dangerous temperatures.
A winter storm impacts the I-90 corridor Tuesday afternoon through Wednesday morning. Moderate to heavy snow accumulations are possible, especially for locations above 5000 feet. Gusty winds (up to 40mpg) will create blowing and drifting snow. Travel is going to be extremely dangerous, especially considering wind chills of as low as -40 to -50 around this time. Conditions improve some Wednesday afternoon, but remaining brutally cold.
A pattern change is expected late week into the weekend. Temperatures begin to warm gradually across the plains, taking a bit longer to warm up in river valleys and in eastern Montana. However, most areas should get into the 30s and 40s by Christmas day. A storm system will bring rain and snow to the region Friday and Saturday, impacting pre-Christmas and Christmas Eve travel. Some freezing rain is possible as warmer air is going to move overhead the colder, shallow air.
SUNDAY NIGHT: Light snow showers. Accumulating a coating to 2 inches by Monday morning. Overnight lows in the -10s, wind chills as low as -30.
MONDAY: Mostly cloudy and frigid with spotty snow showers. Highs in the -0s and -10s. Partly cloudy throughout the night. Overnight lows in the -10s for the Helena area, -20s in central Montana and -30s for the Hi-Line. Wind chills as low as -45.
TUESDAY: Mostly cloudy and frigid with snow showers developing late. Highs in the -0s in central Montana, -10s for the Hi-Line. Steady snow continuing overnight for the I-90 corridor, scattered snow showers elsewhere. Overnight lows in the -10s for the Helena area, -20s throughout the rest of central and eastern Montana.
WEDNESDAY: Dangerously cold. Steady snow tapering to snow showers. Highs in the -0s for the Helena area, -10s for the rest of central and eastern Montana. Gradual clearing overnight as temperatures fall into the -30s and -40s, wind chills as low as -55.
THURSDAY: Dangerously cold. Becoming mostly sunny. Wind chills in the -40s and -50s during the morning. Gradually warming to the -10s and -0s by day's end. Temperatures continue to warm overnight as a SW breeze increases. River valleys remain frigid, also very cold in eastern Montana.
FRIDAY: Scattered snow showers. Highs in the 10s for central Montana, -0s and 0s for the Hi-Line and eastern Montana. Snow, potentially mixing with freezing rain, continues overnight as temperatures fall into the 0s and 10s for central Montana, -0s and -10s in eastern Montana.
CHRISTMAS EVE: Rain and snow showers, possibly mixed with freezing rain. Highs in the low to mid 30s for central Montana, 20s for the Hi-Line and 0s/10s for northeastern Montana. Temperatures falling into the upper 10s and low 20s for central Montana, -0s and 0s for the Hi-Line and eastern Montana.
CHRISTMAS DAY: Scattered rain and snow showers, breezy and mostly cloudy. Highs in the upper 30s and lower 40s for central Montana, 20s for eastern Montana.