6:00 AM, Tuesday, December 19, 2017
Two cold fronts, one Wednesday night and a colder one Friday evening are on the way. We will likely have two snowy days, Thursday and Saturday, as we head into the holiday weekend. The change will seem especially abrupt given that Wednesday is likely to see high temperatures around 60 in many low elevation areas.
Cold & snow, round 1
A cold front Wednesday night and a storm system moving across southern Colorado Thursday will make it seem like winter, and Thursday is the winter solstice. High temperatures on Thursday will probably remain below freezing which will be the first below-freezing day this season for many low elevation areas. Snow is likely to be underway before sunrise from Denver north. Most snow accumulation is expected during the morning to midday hours, but some snow may linger into the evening, especially from Denver south.
3-6 inches: Mountains and foothills. north slope of the Palmer Divide, and places immediate along the foothills (including Castle Rock , western suburbs of Denver, Boulder, Cheyenne)
1-3 inches: Denver/DIA, Colorado Springs, Longmont, Fort Collins
I will update accumulation forecast Wednesday.
Arctic cold & snow, round 2
The next cold front Friday evening will bring an airmass from the Canadian arctic. Temperatures on Saturday and Sunday will struggle to reach 20 even in low elevation areas, and locations along the urban corridor will probably get a night that slips below zero by Sunday and/or Monday morning.
Intervals of snow are likely Friday night and Saturday. Heavy accumulations are not likely, but given the cold, even light snow can have impacts on major highways.
If you are traveling by air this weekend, major airports on the West Coast are probably okay in terms of weather. East Coast airports will be ahead of the arctic air and may see intervals with rain, fog, and low clouds. Chicago should be mainly dry, but with arctic air sweeping in over the weekend, there will probably be delays due to slower ground operations in the cold.