Washington - A fast-moving cold front will plunge the US Midwest into a deep freeze on Tuesday and dump up to a 30cm of snow on parts of the East Coast, forecasters said.In Washington, federal government offices were closed, the Office of Personnel Management said in an early morning e-mail. There was no precipitation in the capital at the start of the morning rush hour.Meanwhile, nearly 2 000 flights in the United States had been cancelled by early Tuesday, according to Flight Aware, a tracking service.The cold front will drop temperatures below freezing as far south as northern Florida. The high in and around Minnesota and the St Lawrence Valley will not top -18°C during Tuesday's daylight hours, forecaster AccuWeather said."Travel conditions will deteriorate with slippery roads and flight delays expected to unfold even in areas that avoid heavy snow," AccuWeather said.The cold front across the eastern half of the country could drop up to 5cm of snow from the Dakotas to the Ohio Valley. The snow will increase as the cold air picks up moisture near the Atlantic coast, AccuWeather said.The mountains of Virginia and West Virginia will probably get up to 15cm of snow. Other sites near the mid-Atlantic and southeastern New England coast could get 15 to 30cm through late Tuesday.For parts of the region, the snow could be the heaviest of the winter. Washington could see the most snow since January 2011, when about 12.7cm fell, AccuWeather said.Code BlueBaltimore officials, expecting up to 25cm of snow in central and southern Maryland, on Tuesday issued a Code Blue alert for potentially dangerous conditions, according to the Baltimore Sun newspaper.Philadelphia was expecting 12 to 25cm of snow, with wind chills in the Poconos mountains dipping down to an icy -20°C, according to local CBS News station KYW-TV.The National Weather Service said the cold air would produce snow downwind from the Great Lakes.The polar front will be something of a repeat of the cold snap that gripped much of the United States at the start of the year. Cold and snow snarled air and road travel, shattered temperature records and contributed to at least nine deaths.In the middle of the cold front on Monday, Grand Marais, Minnesota, recorded -27°C, the lowest temperature in the United States outside Alaska, the weather service said.