It's in the B777 FCOM.
"Crew may elect to obtain weather information from either the company LIDO database, or from SITA. The first preference is LIDO, due to cost benefits. Weather requests should be kept to a minimum and should only be actioned when VOLMETs are not available, the destination forecast is at or below CAT1 minima, the aircraft is within 90 minutes of the destination, and the crew deem the ACARS weather request function the most efficient means of retrieving the weather"