GET READY, WINTER IS WAKING UP...
Old man winter has been taking a big old nap for the better part of the last 3 weeks here in the central Midwest. Mild temperatures and rain instead of snow has been the rule. Heck, we even had a couple of extremely rare tornadoes for good measure Monday. Here's the temperature departures sinc December 28th. From Hudson Bay through the Gulf of Mexico, North America was cooking by January standards!
For some perspective, here's the high temperatures at the Quad City International Airport since December 28th. For the 3 week period ending January 17th the coldest high temperature has been just 30 degrees. Only 2 of the 21 days have seen highs below freezing. The warmest day of the period was the 29th with a record breaking 67! Every single low has been above normal with the coldest reading 15 degrees. To date, the month is running over 10 degrees above normal per day. Man, that is toasty.
Here's the high and low temperature plots relative to average. That is impressive.
Measurable snowfall over much of my area the past 3 weeks ranges from nothing to 2 inches. Notice how quickly amounts go up though in far NW Iowa, SE South Dakota, and SW Minnesota where a swath of 18 to 24 inches extends from ne Sioux Falls to Minneapolis. You are in or you are out!
TIME FOR SOME PAY-BACK
As everybody knows, all good things come to an end and that's definately going to be the case with the mild snowfree environment of January to date. Before we get to snow chances, just a quick mention of something going on in the stratosphere, where a well defined area of low pressure resides known as the "polar vortex". It's at its strongest in the winter and is focused near the North Pole, 10-30 miles above the Earth's surface in a layer known as the stratosphere. It contains the coldest air in the Northern Hemisphere. It can slosh around, stretch, and even break into two pieces.
Generally the plar vortex is stable and keeps the worst of it's cold confined to northern latitudes well removed from the U.S. Every so often (but not every winter), the strong winds that circulate around the vortex weaken or are disrupted. That allows the vortex to stretch and send an Arctic air mass into the lower latitudes of the Midwest. You can see in the graphic the typical stable vortex on the left and the disrupted one on the right.
Now, look at what the EURO is indicating January 19th at 10mb in the stratosphere. Instead of one stable