Refer to figure.
Minimum Control Speed (Air) - V_MCA

When an engine fails or is inoperative in-flight, the rudder is used to counteract the asymmetrical thrust yawing moment, however for a given size of the vertical tail with rudder, there is a speed below which the generated rudder side force is not large enough to counteract the asymmetrical thrust and the heading and/or bank angle cannot be maintained below this speed. This speed is called Minimum Control Speed V_MC.

With regards to this question,
Cold air and higher atmospheric pressure make the air more dense. This makes means the engines are able to produce more power due to being able to achieve a higher mass flow with the higher density air. As power increases, the operative engine requires more rudder authority to maintain directional stability due to the higher amount of thrust. As a result, the airplane requires higher indicated airspeeds to maintain directional stability. Therefore, we have a high V_MCA in this scenario. Since the difference between aircraft's speed and V_MCA is low, the aircraft will also have much reduced controllability. The bigger the difference between both speeds, the better the controllability of the aircraft.