Oberammergau enjoys four beautiful seasons, with temperatures averaging in the 20 to 30 degrees Celsius (68 to 86 Fahrenheit) range, in the summer to -5 degrees Celsius (23 degrees Fahrenheit) in the winter. Actual temperature can be much higher and lower at times. This ensures lots of sunshine for the summer enthusiast and plenty of snow for the winter sports fan.
Please keep in mind the German regulations on the use of winter tyres:
Winter tyres are recommended for the month of October through April. Actually, German law does not set any time limits, but it does clearly state that under icy conditions you must not drive without snow tyres on your vehicle. Fines could apply if you do not follow the regulations.
Oberammergau weather chart