On November 20TH at 3:00 AM PDT for NA, 5:00 GMT for EUW and 02:00 GMT for EUNE, servers will go down for maintenance and the 4.20 patch will be applied.
Here's NA version of the Network Operations maintenance announcement:
"On 11/20/2014, starting at 01:30 AM PST, ranked queues will be disabled in preparation for patch 4.20. At 03:00 AM PST, the servers will be shut down and all games currently in progress will end in a draw and stats will not be recorded. We estimate the battlegrounds will be unavailable for 6 hours."Here's a collection of the patch 4.20 maintenance threads for each server:
I'll keep you updated as more information on what the patch contains and patch notes become available. While the latest PBE content is usually a good indicator of what's to come, please remember that it is tentative and not everything may make it to live. This patch WILL INCLUDE the preseason changes to jungle, objectives, itemization, and more!