UPDATE 1-Snowstorm to hit north central U.S., mid-Atlantic

* Upper Midwest could get 4 to 8 inches of snow

* Washington could get its biggest snowfall of the year

March 4 (Reuters) - A snowstorm was forecast to hit the north central United States on Monday and move eastward over the mid-Atlantic states, giving the Washington area its biggest snowfall of the winter, the National Weather Service said.

Blizzard and winter storm warnings were in effect for parts of Montana, the Dakotas and the upper Midwest, National Weather Service forecaster Bruce Sullivan said.

The storm was expected to dump 4 to 8 inches (10 to 20 cm) of snow from North Dakota to northern Iowa and Illinois on Monday.

Heavier amounts of up to a foot (30 cm) of snow are possible in the upper Midwest and some areas could see freezing rain, leading to hazardous travel conditions, forecasters said. Temperatures in the 20s and 30s were expected.

The storm was forecast to move east, reaching the Ohio Valley, the mid-Atlantic states and the Washington area on Tuesday and Wednesday.

"This will be certainly the biggest snowstorm for the winter in this area," said Sullivan, who is in Maryland.

Forecasting models varied, but the system could dump anywhere from 12 to 20 inches (30 to 51 cm) of snow over northern Virginia and parts of Maryland, Sullivan said.

It will bring a cold, dry snow over the mountains of Virginia and a heavy, wet snow east of Washington, he said.

One of the more challenging aspects of the storm is predicting how much snow would fall on or east of heavily traveled Interstate 95 in Virginia and Maryland, the forecasters said.

"We are into March now. It may start out as a little bit of rain and just how quickly it changes into snow will impact how much we get," Sullivan said.

"Every computer model we're showing right now has Washington getting some snow."