The Chicago National Weather Service Forecast Office has updated the Winter Weather Advisory for later today, tonight and Saturday to include Cook County/Chicago. Thus the portion of the Chicago area south of Interstate-80 and Cook County is under a Winter Weather Advisory for 4 to 6-inches of snow generally from 6PM this evening and tonight through Saturday afternoon. Over the remainder of the Chicago area and northeast Illinois snowfall will gradually taper off as you go north to the Illinois-Wisconsin state line (see blowup of NE Illinois map below).
Much of Missouri, Illinois, Indiana, Lower Michigan and Ohio into Pennsylvania is under the Winter Weather Advisory, as shown on the U.S. map below. A center of low pressure is forecast to move east-northeast out of the Texas Panhandle today with southerly winds opening up the flow of Gulf of Mexico moisture into the developing system.
Freezing rain, sleet and eventually snow is expected to begin over southern Missouri today with rain to the south. As the storm approaches Illinois, snow will form and spread across northern Missouri and southern Illinois – working its way north into the area along and south of Interstate-80 later this afternoon and early evening – eventually covering all of northeast Illinois tonight. . Low pressure will move through southern Illinois Saturday and track off to the east.
Northeast flow on the north side of the storm could prolong snowfall in Chicago by enhancing the impact of lake-effect snow. To the north along the Wisconsin Lake Michigan shoreline and inland a Lake Effect Snow Watch is in effect for 3 to 5 inches of snow with greater amounts along the immediate shoreline possible.
For the 12th time this season, snow’s headed for Chicago. While flurries flutter earthward over sections of the area as early as Friday afternoon and evening—particularly in northern and lakeside areas—-the bulk of the accumulating snow being predicted is to take place from late Friday night into Saturday.
All the elements for snow-production appear in place. A disturbance, lifting out the Texas Panhandle, is to force moist Gulf air back into the cold air here, stoking the precipitation-production process.
What’s more, strong pockets of jet stream winds are positioned to produce maximum “lift” of the air. That’s important because, when air is lifted, it cools to condensation—also fostering cloud and precipitation growth.
Mildest daytime temps in a week precede the incoming snow
Chicagoans are being treated to bit of a break in the arctic cold Friday! Temperatures are to surge well into the 20s, making this the mildest day in 9!
That’s quite a change from the brutally cold temperatures which have gripped the area for a week.
Readings in coming days are to reach the low and mid 30s Saturday then plunge to the teens for a day Sunday as frigid arctic air filters back into the Chicago area.
Best estimate of potential accumulation: 2 to 6 inches—heaviest south, lightest northwest
Two to 6 inches of snow are on the way Friday night and Saturday if current forecast trends hold.
Far northwest sections of the greater Chicago area are likely to see the least snow while various snowfall forecast techniques produce numbers as high as six inches in southern sections of the metro area.
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.
Photo courtesy of Brenda Culver
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.
Photo courtesy of John Kleeman, Mount Prospect, IL