The winter storm moving up from the U.S. southern states has brought heavy snow and freezing sleet to the Northeast on Thursday, closing up federal agencies, schools and airports while leaving half a million people without electricity. "The same storm that brought heavy snow and significant ice accumulations to the Southeast earlier this week has moved up the East Coast, bringing with it significant winter weather to the Mid- Atlantic and Northeast on Thursday and Friday," National Weather Service said. Forecasters said this winter storm could be the biggest of the season to many areas alongside its route. Areas around the country's capital have braced for a dangerous combination of heavy snow, sleet and wind overnight, receiving about 28 cm of snow as of Thursday morning. Although the snowfall has tapered off, all runways of the Reagan National Airport in the capital area have been closed due to accumulated snowfall. Only one runway of the Dulles International Airport in the area is open to aircraft arrivals and departures. The airports have warned passengers of additional snowfall and accumulation later Thursday evening. The winter storm caused significant flight cancellation nationwide on Thursday. As of 3 p.m. ET, 6,300 flights within, into or out of the United States have been canceled, according data released by Flightaware.com The snow and ice has made travel difficult for commuters in downtown D.C. area as the local government urged residents to stay inside and off the hazardous roads. Good news is the federal government has instructed all non-emergency workers to stay at home on Thursday and schools were also closed. Highways appeared to be virtually empty in the morning commute. The nasty storm has also knocked out power to over half a million residents across 14 states from Southeast to Northeast, including Georgia and Virginia. A heavy snowfall between 20 to 38 cm is expected in metropolitan areas of Philadelphia, New York and Boston by the end of Thursday.