I found an interesting article which provides an illustration based on a Germany map with probabilities for snow on Christmas based on long-term averages.
Important facts:
- In Germany there is no place with a snow guarantee, maybe only exception is Zugspitze.
- The probability for snow increases with the altitude of a travel destination.
- The weather forecast horizon in Germany is max. between 5 and 7 days, often shorter around 3-5 days.
- The last white Christmas all over Germany was in 2010, and before that it was in 1981. So it is becoming an increasingly rare event anyway.
Link to full article in German language:
https://www.tagesschau.de/wetter/wetterthema/whitechristmas-100.html
Tip: when you plan to travel Germany by rental car in winter always book winter tires. They are mandatory by law in winter road conditions, i.e., black ice, snow, slush, ice, or frost. So, even when only expecting low temperatures (rule of thumb thumb: lower than 7° C) you may only drive with winter tires (details).
Happy travels.