Thursday is the midpoint of meteorological winter -- a point which should offer
winter-weary Chicagoans at least some solace. The 18 inches of snow which had by late Wednesday
accumulated over a record-tying 9 consecutive days of measurable snow -- only 11.3 inches
falls in an entire January -- has provided the warmth-suppressing snowpack over which
the frigid air has invaded. Snow is extraordinarily reflective, preventing sunlight from
warming the air above.
The current air mass swept into Alaska and the Yukon from Siberia more than three weeks
ago then stalled. But, a band of warm southerly winds, extending from Hawaii into the
49th state, have dislodged the chill and sent it spilling into the Lower 48. Temperatures
within the southbound air mass plunged to 47 degrees below zero Wednesday morning in
Embarrass and 45 below in Sea Gull Lake -- both in Minnesota. It's the reason Chicagoans face
winter's coldest readings, which threaten to include a nearly 40-consecutive hour spell of
subzero readings through midday Friday. It's not the city's longest subzero streak.
That occurred over 100 hours in December 1983. Uninterrupted subzero readings haven't
occurred here over a full calendar day here since Feb. 3, 1996.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune
