I seem to recall that the method for computing wind chill was revised some years ago. How would that have changed the calculation of the wind chill on Christmas Eve 1983?
— Kenneth B. Lejkowski
Dear Ken, Christmas Eve 1983 was brutally cold with a high of 11 below zero and a low of 25 below zero. Its average temperature of 18 below zero made it the coldest day in Chicago’s history dating back to late 1870. The severe cold was exacerbated by very strong winds, which led to the city’s record low wind chill of 82 below zero. Tests determined that the computed wind chill values were too low, so the National Weather Service revised the formula in 2001 to generate more realistic values. Using the new formula, the Christmas Eve 1983 conditions produced a still frigid, but not as extreme, wind chill of 57 below.
The Chicago National Weather Service Forecast Office has issued a Winter Weather Advisory effective from 6PM CST Friday until noon CST Saturday for in general the Chicago area and northwest Indiana along and south of Interstate-80.
The following northeastern Illinois and northwestern Indiana counties are included in the Advisory: In northeast Illinois…LaSalle, Grundy, Will, Kankakee, Livingston, Iroquois, and Ford…In Indiana..Lake, Porter, Newton, Jasper, and Benton. This will include the following cities…Ottawa, Morris, Joliet, Kankakee, Pontiac, Rensselaer, Watseka, Paxton, Gary, Valparaiso, Morocco, and Fowler.
Snow is forecast to spread north and east over the area early Friday evening and persist through the night into Saturday morning with total accumulations of 3 to 6-inches. Snowfall rates could be up to one-half inch per hour reducing visibilities with roads becoming snow covered – making for dangerous travel conditions. The snow should spread north over the remainder of the Chicago area during this same timeframe with a gradient of lesser snowfall north to the Illinois-Wisconsin border.
Note that the southern portion of the Chicago area under the Winter Weather Advisory is but a small portion of a much larger Winter Weather Advisory area (shaded in purple on map below) that includes all or a portion of Illinois south of Interstate-80, Indiana, western Ohio, extreme southern Lower Michigan, and southern Missouri.
Brenda Culver was good enough to send us this shot of geometric ice formations which occurred in this morning’s chill on her windshield. The crystallization process yields some fascinating results in extreme cold–and here’s a great example. Makes for awfully interesting viewing.
John Kleeman celebrates the important role played by our area’s crossing guards—-on duty come cold or snow—to protect children on their way to school.
Kathy Kowalac snapped this wintry, snow-covered scene on a walk with her dogs on her farm–the Dancing Hearts Farm—near Manhattan, IL.
Streamers of snow fall from the clouds Wednesday near Valparaiso, IN.