This story discusses the upcoming refurbishment of Big Thunder Mountain Railroad in Disney's Magic Kingdom, covering its schedule and potential project inclusions.
(UPDATE 12/15/23): Disney recently scheduled a brief refurbishment for Big Thunder Mountain from January 16, 2024, to January 20, 2024, with reopening on January 21, 2024.
Disney has not mentioned what this refurbishment is for, but it appears to be just regular maintenance and not something bigger or adding any additional show elements to enhance the ride.