Flooding is restricting traffic on the Red Hill Valley Parkway.

Hamilton Police and city crews have placed directional signs on a portion of the east Hamilton freeway to keep traffic out of a flooded area.

The flooding was called in at about 10 p.m. Thursday and involves the northbound lane between King Street East and the CN Rail line.

Staff Sergeant Greg Doerr said shortly after 11 p.m. that if the situation gets worse authorities might have to close it down. He said it is being monitored every 30 minutes.

Meanwhile, freezing rain fell in parts of Hamilton Thursday night.

This will be the start of rain that is forecast to fall throughout the night and into Friday morning.

The amount is expected to be between 20 and 40 mms and include thunderstorms. The morning rain will start at 8, but is forecast to fall to zero by the evening.

The rain follows heavy wet snow that blanketed the Hamilton area Thursday afternoon and caused rush hour chaos.

Poor visibility and icy conditions leading to near gridlock across the city. Arteries coming into Hamilton were dealing with heavy traffic and Hamilton police said the Syndenham Hill in Dundas and various Mountain accesses were impassable due to ice. This also included the Highway 6 hill to Clappison's Corners in Flamborough and Centennial Parkway at Mud Street and Winterberry Drive in Stoney Creek.

Hamilton Police Staff Sergeant Mike Spencer were asking everyone who could avoid the roads to stay off them.

"I just got in (to police headquarters at Central station) and can tell you personally the roads are treacherous, very, very icy underneath that snow.

"If drivers can stay off the roads right now we'd very much appreciate it."

The snarled traffic was probably something of a blessing as Spencer said there were no serious ongoing collisions in the lower city at that point, but that the potential was certainly there.

The chaotic weather was the result of an unpredictable, intense weather system that reached Hamilton about 3 p.m., after spawning rain, freezing rain and "thunder snow" across other southern Ontario communities through the day.

Early Thursday, the Hamilton Conservation Authority issued a flood warning for the city in anticipation of what meteorologists then said could be up to 50 mm of rain, plus mild temperatures, over the next 24 hours ending Friday afternoon.

The concern was that snow-melting rain could create conditions for flooding.

But experience on the ground as the storm tracked across the U.S.-Canada border at mid-day Thursday showed a wild-weather mix not limited to rain. There was sleet and snow, including whiteouts, in some parts of Windsor and Detroit, and only heavy rain in others.

Social media reported widespread thunder snow, when it's snowing and thundering at the same time.

The system moved overnight Wednesday from Chicago into the western end of Lake Erie, where flood and rainfall warnings were also in effect.

In Hamilton, the conservation authority advised residents of the potential for flooding in low-lying areas within the city as the rain and melting snow create havoc for 48 to 72 hours.

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Current stream flow conditions are near normal for this time of the year, the conservation authority said, but "the potential combination of precipitation and snowmelt . may result in rapidly increasing flows and water levels in area watercourses."

It is advising people to exercise caution near all water bodies, as fast moving water and slippery banks may pose a significant hazard.

On Wednesday, city crews were racing to clear snow from hundreds of flood-prone storm water inlets across Hamilton in preparation for the storm.

City superintendent Bob Paul said crews were clearing "priority" grates, inlets and culverts in the lead-up to the rain - particularly about 900 "flooding hot spots" spread throughout the city.

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In the lower city, wards 1 and 5 are vying for the most storm water outlets subject to chronic flooding, with around 75 each. The most flood-prone suburb is Dundas with 161 hot spots, while Ancaster and Binbrook each have more than 100.

Motorists are probably most familiar with the dramatic consequences of overland flooding at old rail underpasses such as Kenilworth Avenue, Centennial Parkway and Birch Avenue, where cars have become trapped in the past.

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On the upside, Environment Canada meteorologist Geoff Coulson said the flood risk may be lessened because the warm spell will be short-lived. Temperatures are expected to hit a high of 3 C on Thursday and 5 C on Friday. By Sunday the temperatures are expected to dip below freezing again.

- Why storm flooding is inevitable in Hamilton