The coldest air of the season will be diving south with a polar express beginning this weekend, with all 50 states in the US, including Hawaii, expected to reach below freezing temperatures on Monday morning. The Metro forecast calls for temperatures closer to February norms after spring-like conditions so far this week.
Expect light snow Thursday through Monday in Bonners Ferry, with above normal temps in the mid to upper 30s until Saturday, when 30 degrees is the expected high. Look for 37 Sunday, then cooling into mid- to upper-20s for highs on Monday and into the teens overnight.
It will be a little cooler and not as snowy in Troy and Libby, with overnight lows into the teens beginning Friday night.
In Creston, a slight chance of snow Thursday and Saturday and cooling down Saturday, with -4 for a high and -15 overnight … next Wednesday, -11 for a high and dropping to -22 overnight.
The polar vortex is a large area of low pressure and cold air surrounding the Earth’s North and South poles. The term vortex refers to the counter-clockwise flow of air that helps keep the colder air close to the poles, as depicted on the left in the graphic.
Often during winter in the Northern Hemisphere, the polar vortex will become less stable and expand, sending cold Arctic air southward over the United States with the jet stream, as shown on the right.