CHICAGO - - A snow storm that has taken a breather through Friday afternoon threatens to strike with renewed vigor Friday night and could leave up to 8 inches of snow by the time things calm down again early Saturday.

 
The first punch from the storm Friday morning snarled traffic for the morning rush and led to the cancellation of more than 200 flights at O\'Hare.

A National Weather Service winter weather advisory re mains in effect for northern Illinois and northwest Indiana until 6 a.m. Saturday.

The forecast calls for snow to pick up in intensity Friday night, mainly after 8 p.m. The weather service is calling for a 100 percent chance of snow overnight, with new accumulation of 3 to 5 inches possible.

The snow will continue through the night, and should mostly be over by 8 a.m. Saturday, according to the weather service. When it\'s all over, there could be up to 8 inches on the ground in some northern suburbs, up to 6 in the city and 4 or less to the south.

The city’s Department of Streets & Sanitation deployed 184 snow-fighting trucks to the main roads about 2:30 a.m. Friday, according to a department release.

An update from Streets & San said those trucks were moving to the side streets for plowing only about 2:30 p.m. when the snow let up, but were ready to resume work on main roads later Friday. It said snow is expected to resume as early as 7 p.m.

Once the snow system has left the area and main routes are plowed and salted, trucks will again be shifted to the side streets to plow and salt , according to the release. That is not expected to occur until Saturday morning.

At the airports, as of 3:30 p.m., delays at O\'Hare are averaging 15 to 30 minutes, according to a release from the Department of Aviation.

Airlines have canceled more than 200 flights Friday, according to the release, which said there were no delays as of 3:30 p.m. at Midway and only minor cancellations.

Passengers traveling through O\'Hare or Midway this evening should check their airline\'s Web site or contact by phone to check the status of their flight. 

The storm brought traffic on the expressways to a crawl during the morning rush, prompting ISP District Chicago, Elgin District and District 15 (Tollways) to institute the emergency snow plan, meaning ISP will only be responding to accidents with personal injury or non-drivable property damage, according to an ISP release.

A motorist in drivable property damage crashes should exchange information in a safe location and make a report at the nearest State Police District within seven days.

As of late Friday morning, ISP has responded to numerous calls for service ranging from motorist assists, vehicles driving off the road and multiple vehicle crashes involving minor injuries, the release said.

Motorists are urged to use extreme caution when driving, slow down and allow plenty of time to make it safely to their destinations while yielding to emergency vehicles including highway maintenance vehicles displaying oscillating, rotating or flashing lights, the release said.

Scott’s Law requires a driver to change lanes, if it is safe to do so, or reduce speed and proceed with caution when approaching a stationary emergency vehicle displaying flashing warning lights, the release said.

ISP indicated that hazardous conditions are expected throughout the day Friday and there are the following safety tips motorists should adhere to:

--Plan ahead and makes sure before leaving that your trip is necessary;

--Don\'t crowd a snow plow and remember the operator\'s field of vision is restricted;

--Watch out for black ice and roads that appear treacherous and take it slower when approaching intersections, off-ramps, bridges and shady areas because they are all prone to icing;

--Dress warmly and in layers of loose-fitting, lightweight clothing in anticipation of emergencies;

--Make sure someone is aware of your travel route;

--Always keep an emergency car care kit that contains jumper cables, flares or reflectors, windshield washer fluid, a small ice scraper, traction material, blankets, non-perishable food and a first aid kid;

--Always carry a cell phone and wear a seat beat.

The snow could cause havoc with the evening rush as well.