Small Transport
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Commercial
Situational Awareness
Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action
Aircraft; Environment - Non Weather Related; Human Factors
During the climbout of RNO; stronger than expected downdrafts limited the aircraft climb rate and cruise altitude ultimately leading to ATC identifying as an emergency. During the climb; ATC was advised of the aircraft's slow climb rate and provided a climb vector to join J5. This and LLWS were expected per the issued Airmets and Pireps. However; upon reaching 14;000 feet MSL; the downdrafts became much stronger than anticipated and the aircraft began to sink. Max power and pitch for the conditions were utilized in an attempt to maintain altitude; but the aircraft continued to sink. ATC was informed and vectors were requested to the Sacramento Valley area where terrain would not be a factor.ATC provided their minimum vectoring altitude of 13;000 feet MSL and assigned a heading that would take the routing over South Lake Tahoe. As the aircraft approached the mountain range between the Reno valley and Tahoe; strong turbulent air; presumably from a mountain wave; caused the aircraft to begin to sink again. ATC was informed and alternate vectoring through a pass to overfly Lake Tahoe was requested. At this point ATC informed me that they were identifying an emergency on my behalf since the altitude was below their minimum vectoring altitude and provided vectoring.Once the aircraft had cleared the pass; I requested a block altitude between 13;000 and 15;000 since maintaining a steady altitude was proving difficult due to both strong down and updrafts. Despite this; I was able to climb and maintain 14;500 within reason. During these events the aircraft dipped approximately 300 feet below minimum vectoring altitude and only momentarily. The reason for the decision to continue instead of returning to RNO primarily had to do with the strong LLWS; turbulence; and downdrafts experienced right after rotation. Ultimately; it seemed safer to continue to the valley than risk possible loss of control on landing with a heavier aircraft. Also with the routing provided; there were multiple outs available had the situation become worse.Cause: Stronger than anticipated downdrafts; Turbulence; LLWS; and some downdrafts from mountain waves were expected and discussed with dispatch. The weather; while poor; should not have prevented the aircraft from reaching and maintaining a safe operating altitude for the flight.Response: Upon reaching ZZZ; both the Chief Pilot on call and dispatch were alerted.Suggestions: The main ways to prevent this from occurring again would be to have an alternate route that would take the aircraft through lower terrain with similar forecasted conditions or to cancel the flight with the same forecasted conditions.
Air taxi pilot reported strong up and down drafts prevented the heavy aircraft from climbing as expected in a mountainous area.