UPDATE 1-Powerful snowstorm hits U.S. East Coast
* Region is major U.S. market for home heating fuel
* Heavy snow, unseasonable cold forecast
* U.S. government offices in D.C. area close early
(Updates with new details throughout)
By David Morgan
WASHINGTON, Feb 5 (Reuters) - A powerful storm slammed the U.S. mid-Atlantic on Friday, threatening record snowfall in a region heavily dependent on home heating oil and natural gas supplies.
Forecasts calling for 20 to 30 inches (50 to 76 cm) of snow and near-blizzard conditions from Virginia to southern New Jersey prompted U.S. government offices in the Washington area to close their doors four hours early.
President Barack Obama, who previously has made fun of the reaction in Washington to small amounts of snow, was not taking this storm lightly.
"I think even a transplanted Hawaiian to Chicago has sufficient respect for a forecast of nearly two feet (61 cm) of snow," White House spokesman Robert Gibbs said.
"And being from Alabama, I am happy to inform you I will be getting off the road and watching you all try to drive," Gibbs joked with reporters.
The Smithsonian museums and the National Zoo will be closed Saturday in Washington.
News of the storm brought school closings and long lines at supermarkets as frenzied area residents rushed to stock up on groceries and other supplies ahead of a traditional party weekend for watching the Super Bowl football game on Sunday.
Virginia, Maryland and the District of Columbia each declared snow emergencies. The declarations allow states to activate emergency agencies including the National Guard to help prepare for the wintry onslaught and cope with its aftermath.
The giant storm system was expected to engulf the cities of Baltimore, Washington, D.C., and Philadelphia in a heavy blanket of snow, while bringing heavy rain to sections of the southeast including the Carolinas and Georgia.
The cold helped boost New York's spot natural gas market toward winter season highs, where prices reached about $11.50 per million British thermal units on average, up more than $4 from Thursday.
Spot gas for Chicago rose 10 cents to above $5.70. Meanwhile, heating oil was little changed.
Unseasonably cold temperatures were expected in the storm's wake next week in the U.S. Northeast, which is the world's biggest heating oil market, and the Midwest, a large natural gas demand center.
"Once we get through the weekend storm, much colder air will invade the Northeast and mid-Atlantic. The outlook for the northeast third of the country next week is looking much colder than normal," said Jim Rouiller, a senior energy meteorologist at private weather forecaster Planalytics.
Airlines began canceling scheduled flights for late Friday through Saturday at the Washington-Baltimore area's three main airports.
Amtrak suspended most of its passenger rail service to destinations south of Washington but said its Silver Service trains between New York and Miami would operate normally.
The same weather system brought heavy rains to parts of the southeastern United States including the Carolinas and Georgia while fueling itself with fresh moisture from the Gulf of Mexico and the Atlantic Ocean.
The National Weather Service issued a winter-storm warning for Washington until late Saturday evening with isolated areas in for more than 30 inches (76 cm) of snow. Local weather forecasters said the storm could bring the heaviest snowfall in 100 years to the area.
Authorities in some states urged local residents to work from home rather than brave a difficult Friday evening commute.
State dispatchers ordered thousands of trucks equipped with plows and road salt to strategic locations where they could begin the job of clearing roadways once snow began falling.
Across the country on the West Coast, weather forecasters issued a winter storm warning for Southern California's mountains on Friday, calling for heavy snow and gale-force winds. Snow accumulations up to nearly two feet (61 cm) were expected through Saturday in higher elevations, and mountain travelers were warned that visibility could be cut to near zero.