Winter storm warnings have been issued for six counties in central and southern New Jersey as the state braces for up to 6 or 7 inches of snow and potentially dangerous travel conditions on Friday. The warnings take effect at 4 a.m. Friday and run until 6 p.m. Friday in Burlington, Camden, Gloucester, Monmouth, Ocean and Salem, the National Weather Service said. Most other counties in the Garden State remain under winter weather advisories, because lighter snow is anticipated. “Travel could be very difficult,” the weather service said in its storm warnings. “The hazardous conditions could impa…