Beechjet 400
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 6
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Weather
Aircraft X was on a vector northbound; issued 100. I informed them of moderate turbulence in the airspace; they acknowledged and confirmed the report. I cleared them direct ZZZZZ and issued descent to 085; which was the MVA in that area. Aircraft X read back correctly. While still in the 085 MVA; I observed Aircraft X descending through 080. I told them to climb and maintain 085 due to higher terrain. They stated they were getting bumped around pretty badly and were attempting to climb. I asked them if they had the terrain in sight and could maintain visual; they replied affirmative. I observed a descent to 078 at which point they were exiting the 085 MVA and in a 074 MVA. I instructed them to cross ZZZZZ at or above 076 cleared for the RNAV Runway XX; ZZZ. Aircraft X landed without further incident.I don't have any recommendations. This seemed to be a weather-related event due to the strong winds; mountain wave activity; and turbulent rides.
TRACON Controller reported an aircraft descended below the MVA as a result of getting bumped around due to turbulence and mountain wave activity.