A strengthening weather system appears ready to strike the D.C. area Tuesday night as an enormous winter storm, forcing a scramble among emergency planners who are bracing for more than five inches of snow in a region that has been snow-starved so far this season.

"This is a significant winter storm," said Ken Widelski, a National Weather Service meteorologist. "Washington is tricky because it will be along the rain-snow line for a while. We certainly can't rule out at least six inches there."

Forecasters said the storm, which could produce more than a foot of heavy, wet snow in some locales along with high winds, would likely create dangerous conditions for motorists and threaten the region's power supply.

"The prediction seems to be getting worse as we speak," said David McKernan, director of the Fairfax County Office of Emergency Management. "Our concerns are power outages and traffic issues."

Conditions are expected to begin deteriorating late Tuesday evening before the precipitation intensifies after midnight and ends Wednesday afternoon. Officials were urging residents to travel ahead of the storm.

But authorities were simultaneously preparing for the storm's aftermath, and Metro spokesman Dan Stessel said the rail system would likely continue to operate.

"The system can operate fairly normally in five inches of snow," Stessel said. "You may see some minor delays, but nothing too significant. It's really the eight-inch mark where you start running into some problems."

Bus routes, Stessel said, were more likely to be adjusted because of conditions, and he said customers should allow extra travel time.

"This won't be the kind of day where you'll want to be running for a train," he said.

In Virginia, which meteorologists expect will suffer the worst of the storm, Dominion Virginia Power said it was already talking with utilities in the South about sending extra crews to help restore electricity.

"We do anticipate the possibility of power outages if the forecast is accurate and we have the wet snow that is being called for," said Le-Ha Anderson, a Dominion spokeswoman. "Crew-wise, equipment-wise and maintenance-wise, we are all ready to go."

Washington has not seen a major March snowfall since 2009 when it recorded more than five inches. The area's March snowfall record dates back to 1914, when the District received more than 19 inches.

Mother Nature has taunted the region this season with repeated dustings, but Widelski said forecasters were certain that the looming storm was not a bluff, even though temperatures were expected to hover around freezing.

"Our confidence is high now," Widelski said. "What's tricky in early March is you get a higher sun angle. But if you snow heavy enough for a long enough time, that could overwhelm the warm ground."