December 1 is the first day of winter. The countdown for 'Nuclear Winter' led to December 1. Maybe it was just a silly second countdown for Winter?

No, December 21 is the first day of winter. The timer goes to around the 13th.

What do the coded words mean though?

What? Winter starts on the solstice, aka, December 21st.

Huh. Well, thanks for correcting me. I always thought December, January, and February were Winter. Then, March, April, and May make up Spring... June July August - Summer... And September, October, and November for Autumn?

"Winter" starts depending on reference - Winter half or quarter, academic or astronomic (and northern or southern hemisphere, but northern is typically assumed so it doesn't count). In Norway, winter starts on 21-23 of November. And spans thru December, January and 2/3rd of February.

It's a Ceasar Cipher. I'm not quite sure how many points though.

KVNGR REV ALPHA PPS VT PIZ UHMYLPVOQ CM XHWMZP. NBJB SPI'F BYQS QT D'Y BYFGEOB FI VQDYL MAQ. -NGQHT 5120-
Nuclear winter has come

http://www.gamesas.com/topic/1479703-fallout-4-speculation-suggestions-and-ideas-170/