A winter storm warning was posted this morning by the National Weather Service for the fourth nor’easter expected to ravage the state this month.The forecast, once again, is dire for the Boston area, South Shore and points west as far as Springfield.The warning takes effect for most of the state tomorrow at 8 a.m. and will remain in force until at least 8 a.m. Thursday, as 10 to 14 inches of snow is likely to top off what remains from last week’s blizzard.The weather service said travel “will be very difficult to impossible” during the storm.