Farmer's Almanac after 230 years averages as well as our best modern US weather forecasts.

The Old Farmer’s Almanac has been making yearly long-term weather forecasts for 230 years. We pay attention to them because they are normally 80% accurate. They did not do as well last winter but were 72% in predicting the direction of temperature change, and 78% accurate in the change in precipitation. This is pretty remarkable because while the U.S. weather forecasts are 90% accurate five days in advance, they are only 80% accurate seven days out. The Old Farmer’s Almanac forecasts are far less specific, they only predict the direction of change, but their forecasts are for twelve months in the future, quite impressive.

From Wattsupwiththat.com and written by Andy May.
It's not based on what the groundhog saw in February.  From the start with Robert Thomas in1792, it's been based on solar cycles, blended with temperature records and increasingly incorporating large weather elements that are affected by insolation.  Currently several dozen elements are factored in like the El Nino current and the North Atlantic Oscillation.