The Washington area will be guaranteed a white Christmas this year.  WeatherEye Meteorologist Paul Trambley says the criteria for a white Christmas is having at least one inch of snow on the ground on Christmas Day.  He says the snow could fall before Christmas and still qualify.  Trambley adds that depending on where you are in Iowa determines how much of a chance you have of seeing a white Christmas.  He says based on the last 50 years of data, southern Iowa has a one in three chance of having a white Christmas, where northern Iowa has a 2 out of three chance of having a white Christmas.  To hear the complete interview with Meteorologist Paul Trambley, Radio Plus.