The Future Tense blog at Slate.com provided some good commentary on seasonal forecasting in their blog entry from October 17. Winter seasons are the easiest to predict, because they are generally tied to the presence or absence of El Nino in the Eastern Pacific Ocean. This is especially true in the southern portions of the Southeast and in the upper Midwest. However, other patterns are more difficult to predict because they are based on shorter term variability and are highly dependent on what your location is. Weather patterns like snow or ice storms are especially hard to predict because small changes in local weather can affect where or if the frozen precipitation falls. You can read the blog here.