How accurate are Punxsutawney Phil's Groundhog Day forecasts?

How accurate are Punxsutawney Phil's Groundhog Day forecasts?

How accurate are Punxsutawney Phil's Groundhog Day forecasts?

As legend goes, if Punxsutawney Phil sees his shadow on Groundhog Day, you should expect six more weeks of winter; if he doesn’t, plan for spring.
How accurate are Punxsutawney Phil's Groundhog Day forecasts?