A slow-moving system that draped a warm front across Louisiana, dumping rain and closing roads, waterways and schools Wednesday, was predicted to keep on drenching the state through Thursday afternoon, meteorologists with the National Weather Service said.

The front, held in place by a low pressure system over south Texas and a high to the north, is a classic pattern for heavy rains more typical of early spring than winter, said meteorologist Fred Zeigler, of the weather service’s Slidell forecast office.

The unseasonably early downpour dropped 4 to 6 inches of rain across much of the Baton Rouge metro area, with parts of Livingston Parish seeing 8 inches or more, Zeigler said.

The region will remain under a heavy rain advisory and flash flood watch until 6 p.m. Thursday, he said. A flash flood watch means that conditions may develop that lead to flash flooding.

Residents can expect an additional 2 to 4 inches of rainfall across the region Thursday, with isolated areas receiving more, before the system moves north toward the Great Lakes on Friday, Zeigler said.

Mayor-President Kip Holden advised East Baton Rouge Parish residents in a news release Wednesday to expect flooding and possible sewer backups.

“We cannot overstress the importance of the care we need to take,” he said in the release.

City-parish personnel will have barricades on standby in case of any flooding, said Todd Teepell, assistant to the director of Public Works.

Residents of East Baton Rouge, Livingston and Ascension parishes also may pick up sandbags at their local fire stations, officials said.

Rivers affected by the lingering storm system are expected to crest above flood stage Thursday or Friday, Zeigler said.

The Comite at Joor Road, at 21.88 feet as of 3 p.m. Wednesday, was expected to rise 3 feet above flood stage to 23 feet by midnight Wednesday, he said.

By Thursday evening, the Amite at Denham Springs will rise to a projected 30.5 feet, he said. Flood stage is 29 feet.

Likewise, the Tickfaw at Holden will crest at 16 feet, a foot above flood stage, on Friday evening, he said.

The Tangipahoa River at Robert already had experienced minor flooding Wednesday, rising to 16.7 feet, or 1.7 feet above flood stage, with a crest of 17.5 feet projected for Thursday evening.

Livingston and Ascension parish authorities ordered the closure of waterways in both parishes to all but emergency boat traffic as of 6 p.m. Wednesday, citing concerns about possible debris in the rivers and wakes caused by the boats.

State Police warned that the additional rainfall and cresting rivers could lead to flooding along state and local roadways.

Drivers were urged to avoid being on the roads unless absolutely necessary, to be cautious of high winds, and to slow down to avoid hydroplaning and to account for increased stopping times, Trooper 1st Class Stephen Hammons said in a news release Wednesday.

Motorists also were advised to avoid roads that are under water and not to attempt to drive around barricades, even if the route appears safe, he said.

Road closure information is available by calling 511 or visiting http://www.511LA.org or http://www.lsp.org.

Hazardous road conditions may be reported by calling *LSP (*577).

Widespread flooding in Livingston Parish on Wednesday left 89 roads underwater and more than 20 closed to traffic, said Mark Harrell, director of the Livingston Parish Office of Emergency Preparedness.

The access road to Our Lady of the Lake Livingston in Walker flooded, but gravel was being added Wednesday afternoon to make the hospital’s entryway safer, Harrell said.

Three large Office of Emergency Preparedness vehicles were kept busy pulling cars out of flooded areas across the parish, and a few cases of house flooding were reported, Harrell said.

Flooding also was extensive in Ascension Parish, where water levels rose to the banks of bayous or beyond in some locations, including Francois, New River and Black.

The East Ascension Consolidated Gravity Drainage District’s array of pumps in the McElroy Swamp southeast of St. Amant and in Sorrento began pumping at 5 p.m. Tuesday and continued to run Wednesday, said Lester Kenyon, parish government spokesman.

The pumps drain much of Ascension’s east bank.

In Gonzales, a few homes on West Roosevelt Street across from Gonzales Primary School received 2 to 4 inches of water inside, residents and property owners said.

Just north of the city limits Wednesday afternoon, parents drove on side streets or through high water overtopping Cannon Road to pick up their children at Le Chateau Des Jeunes, a private day care located between Black Bayou and a tributary.

High water on several roads in St. Helena Parish prompted schools there to close at 1 p.m. Wednesday, Superintendent Kelli Joseph said.

St. Helena’s high school and elementary school, as well as the Recovery School District-run middle school, will remain closed Thursday, school officials said.

Advocate staff writers Bob Anderson, David J. Mitchell and Robert Stewart contributed to this report.