by Mike Hamernik twitter @Mike Hamernik
Calm winds and clear skies overnight led to patchy dense fog as well as a heavy frost this morning. The frost is resulting in slick spots on bridges and overpasses. Fog is especially thick in northwest Indiana where visibility is limited to just a few hundred feet along stretches of Interstates 80, 90, 94 and 65. The fog should quickly dissipate by 9AM.
RIGHT: Low lying dense fog in Akron, Indiana shortly before 7AM
by Mike Hamernik twitter @Mike Hamernik
Rain changed over to snow last night on the northern fringe of a large precipitiation shield that still stretches from Texas to the Midwest. The majority of the rain, snow and sleet fell along and south of the I-88/Eisenhower corridor. While there was little or no accumulation in northeast Illinois, the snow did stick just to the southeast of Chicago.
Over six inches of snow fell in Fort Wayne, Indiana this morning. As of 8AM, radar indicates the heaviest snow has shifted east into Ohio. Periods of light rain and snow will persists this afternoon, mainly along and south of Interstate 80. However any additional accumulation will be limited to one inch or less. Recent snowfall reports include:
6.8" Fort Wayne, IN
5.5" Columbia City, IN
1.2" Valparaiso, IN
1.0" Crown Point
0.9" La Porte, IN
0.6" South Bend, IN
0.6" Crete, IL
0.4" Homewood, IL
0.2" Peotone, IL
TOP RIGHT: A wet, slushy snow in Akron, Indiana.
TOP BOTTOM: Parkview Field in Fort Wayne, Indana.
by Mike Hamernik twitter @Mike Hamernik
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UPDATE 8:45AM: A few snowfall accumulation reports from across the Chicago area
2.3" Kenosha, WI
1.4" Bull Valley, IL
0.9" Lake Geneva, WI
0.8" Gurnee, IL
0.8" Wonder Lake, IL
0.2" Batavia, IL
0.1" Winnetka, IL
ABOVE: Snow obscuring the Chicago skyline at 8:45AM
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UPDATE 8:01 AM: Bursts moderate to heavy snow are being observed over some of Chicago's northern and western suburbs. The snow will end by 11AM with up to 1" of accumulation.
RIGHT: Illinois RT 22 at RT 83 near Long Grove and Vernon Hills.
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6:30AM: A weak and relatively moisture starved low pressure system is racing across southern Wisconsin this morning producing several fast moving bands of snow. The snow won't last long as the system will be east of Chicago by 11AM. The most significant accumulation (0.5" to 1.0") is expected to occur over Chicago's northern suburbs.
RIGHT: Snow falling at Grand and Sheridan Ave. in Waukegan shortly after 5AM
by Mike Hamernik twitter @Mike Hamernik
Around 1 inch of snow fell across the Chicago metro area overnight leaving many secondary and untreated roads slick and icy. Walking may also be a hazardous adventure this morning as some sidewalks, parking lots and stairs are snow and ice covered.
Here are a few snowfall totals from across region:
0.8" Chicago- O'Hare (official)
1.8" Westmont
1.8" Downers Grove
1.4" Elgin
1.4" Romeoville
1.2" Woodridge
1.2" Lakes of the Four Seasons, IN
1.0" Naperville
0.6" Gurnee
0.5" Chicago- Wrigley Field
0.3" Chicago- Hyde Park
ABOVE: Sunshine reflecting off a fresh snowcover in Northbrook, Illinois this morning
by Mike Hamernik twitter @Mike Hamernik
Freezing drizzle and very light snow likely through mid-afternoon
Patchy light freezing drizzle, freezing fog and flurries are possible across the Chicago area through late afternoon until temperatures rise above the freezing mark. Until surface temps reach 32 or 33 degrees, untreated road surfaces may be icy due to the light misty precipitation.
A Winter Weather Advisory is in effect for the I-39 corridor counties of De Kalb, Boone, La Salle, Winnebago, Lee and Ogle until 6PM tonight.
A Freezing Drizzle Advisory has been posted for portions of western Illinois including Galena and Moline as well as stretches of Interstates 80 and 88 until 6PM Sunday.
RIGHT: Freezing drizzle advisory for western Illinois as well as eastern Iowa.
Fog expected to be dense tonight
Warm moist air overrunning a thick blanket of snow that covers most of northern Illinois is a perfect recipe for dense fog. Fog may reduce visibility to 100 feet at times tonight, especially in rural areas.
RIGHT: Dense fog in the Champaign-Urbana area headed north toward Chicago.
Rain and thunderstorms tonight
As this potent storm system starts to intensify this evening, showers and thunderstorms are expected to break out over the middle part of the country. A few of these thunderstorms may push as far north as Chicago. A major severe weather and tornado outbreak is possible from southern Illinois and southern Indiana southward to the Gulf coast. The main severe weather threat will lie south of a St. Louis to Champaign to Fort Wayne line. Here in the Chicago area, the threat of any organized severe thunderstorm activity remains low for a number of reasons, including the lack of sufficient low low level moisture as well as the fact we have a 5" blanket of snow on the ground.
by Mike Hamernik twitter @Mike Hamernik
Lake effect snow has been falling lightly this morning over portions of southern Cook county as well as northern Lake County in Indiana. This plume of snow is impacting the Dan Ryan Expressway as well as the Chicago Skyway. Accumulation will be less than 1" over southeast Cook county and the snow will end by early Saturday afternoon as winds aloft turn southerly.
RIGHT: 6AM to Noon projected snow accumulation from our in house RPM computer model.
Over 90% of the Chicago area snowfall reports from Friday's storm fell within a 5" to 8" window. The heaviest snow was concentrated in a small 5 mile wide band that fell over northern Will County eastward into central Lake County Indiana.
The offical numbers that will go in the books
5.4" Chicago- O'Hare
7.3" Chicago- Midway
Snowfall roundup courtesy of the National Weather Service
JOLIET LOCK/DAM (WILL)........................8.3
PLAINFIELD 1SW (WILL).........................8.2
DOWNERS GROVE 2SE (DU PAGE)...................8.0
SCHERERVILLE (LAKE IN)...............8.2
JOLIET 2N (WILL)..............................8.0
MONEE (WILL)..................................7.7
by Mike Hamernik twitter @Mike Hamernik
RIGHT: Winter Storm Warning Friday and Friday night for 4" to 8" of snow. Most of the snow will fall between 10AM and 7PM. 
UPDATE: 9:29PM: The National Weather Service has replaced Friday's Winter Weather Advisory with a Winter Storm Warning. The warning means there is the potential for 6 inches or more of snow.
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4:30PM: A Winter Weather Advisory has been issued by the National Weather Service effective Friday and Friday night for most of the Chicago area.
WHAT, HOW MUCH: This advisory replaces the Winter Storm Watch issued yesterday. Despite the change in "headlines" from the National Weather Service, there is little change to the going forecast of 4 to 8 inches of snow by Saturday morning, with locally heavier totals of 9 inches possible in a narrow 5-10 mile wide band.
South of the advisory area, 1" to 3" of snow is expected at this point. Check back with us throughout the night and during the storm tomorrow, as storm totals will need to be adjusted if the system deviates from it's expected track.
WHO, WHERE: Locally, the advisory includes Cook, Lake(IL), McHenry, Kane, De Kalb, Du Page, Kendall, Will, Lake(IN), Porter(IN), LaPorte(IN), Berrien(MI), Kenosha(WI) and Walworth(WI) counties.
WHEN: Snow is expected to move in to northeast Illinois between 7AM and 10AM Friday, lasting most of the day and into the evening before tapering to flurries Friday night. Due to the fact the majority of the snow will be falling on a weekday, and during daylight hours, this is expected to be a high impact storm for commuters.
WHY: Because it's January in Chicago.
BELOW: Winter Weather Advisories extend beyond Chicago into Indiana, Michigan, Wisconsin and Iowa.
by Mike Hamernik twitter @Mike Hamernik
Sometimes snowstorms are all about timing. Several factors are coming together to produce what looks to be a medium to high impact snowstorm for Chicago area commuters. A few of these factors are:
1) The majority of the snow will fall during the day.
2) The heaviest snow is expected during the afternoon and evening.
3) It's a weekday.
4) It's a Friday.
5) Cold temperatures- Road crews will be challenged by temperatures well below freezing, in the teens to around 20 degrees. Chemicals used to melt snow and ice don't work as well, or as quickly as they do at 30 to 32 degrees.
The bottom line- all 4 to 8 inch snowstorms are not equal. Chicago snowstorms that hit at night, or on the weekend, tend to have a much lower impact on travel.
BELOW: Forecast map for 11:30AM Friday. Snow is expected to overspread most of northern Illinois during the late morning hours.
