Server Maintenance: Patch 4.19 (Source)You can find all changes presumed to included into this patch in our complete 4.20 PBE cycle article !
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.
League of Legends : Patch 4.20, servers maintenance
Servers will be unavailable tonight. Riot Games will deploy the new 4.20 patch on the live servers.