Two fronts will slide across Missouri and Illinois this week, and that means two separate shots of very cold Canadian air. The second front will usher in the coldest air of the season so far, possibly the coldest air in several years.
Front #1 arrives Monday evening. It looks like it will be blowing through between 7:00 PM and Midnight. Temperatures will climb into the 40s ahead of the front, but highs behind the front will only be in the 20s Tuesday. With gusty northwest winds, it will feel even colder.
Front #2, the leading edge of even cooler air, will be rolling through Wednesday evening. After a brief warm-up into the upper 30s Wednesday afternoon, temperatures will tumble into the single digits Wednesday night and Thursday morning, only bouncing back into the teens Thursday afternoon. Friday morning looks to be the coldest period of this entire chilly snap, with lows possibly near zero!
It's been more than 10 years since the official St. Louis weather reporting station recorded a temperature below zero, the longest such period in recorded history. The last time we dipped below zero was January 5, 1999, when the mercury dropped to -5 degrees.
Snow on the ground can certainly have an impact on local temperatures, esepcialy overnight. In fact, a quick review of the last 10 times St. Louis has dipped below zero reveals that snow was on the ground for 8 of those occurrences. Here are the last 10 cold air outbreaks that resulted in sub-zero temperatures...
January 5, 1999: -5 (snow depth of 7 inches)
January 12, 1997: -3 (snow depth of 6 inches)
February 3 1996: -12 (no snow cover)
January 18 1994: -8 (snow depth of 3 inches)
February 18 1993: -1 (snow depth of 6 inches)
December 22 1989: -16 (snow depth of 4 inches)
February 12 1988: -3 (snow depth of 5 inches)
January 27 1986: -1 (no snow cover)
January 20 1985: -18 (snow depth of a trace)
January 20 1984: -6 (snow depth of 1 inch)