January gave the windiest start of the year to Missouri in almost 30 years. Wind puts the chill in wind chill.
"Those who think winds are chillier than usual are right," says Pat Guinan, state climatologist, University of Missouri Extension. The cold and wind continues into February.
Cold dominated the weather reports since Jan. 1. "Preliminary data for January indicates the statewide average temperature was 25 F. That’s almost 5 F below long-term normal," Guinan says.
With the winds accompanying frequent fast-moving fronts, the wind chills regularly drop to minus 10-30 degrees.
A polar jet stream set up from northwest to southeast across the state. That let several Arctic cold fronts barrel through the region.
"Those fronts brought reinforcing shots of frigid air," Guinan says.
The mark of cold weather is when the daily high temperature doesn’t rise above zero degrees. That happened often across northern and central Missouri. That hadn’t happened since December 1989, he adds.
Winds are driven by differential between high-pressure and low-pressure areas. The Arctic cold fronts bring lower air pressures with them. Then the following high-pressure zones behind the fronts rush to fill the lows. The gradient between the two determines wind velocity.
"The differential is like when you push the valve on an inflated tire," Guinan says. "The energy gushes from high pressure to low pressure." The colder the air, the higher the density and the greater the air pressure.
"This winter, the polar jet dipped more often and deeper into the United States than usual," he says.
What’s unusual was that the cold fronts lacked moisture this winter, Guinan says. They delivered less than normal water despite deep snows in parts of southern and east-central Missouri. The snow in early February across the north was light and fluffy.
Moisture-laden Gulf of Mexico air has been blocked from encountering the cold fronts, which normally trigger precipitation. With few exceptions, the snow came from Pacific moisture brought in on the jet stream.