The pilot and passenger departed from the uncontrolled airport on a snow packed runway and flew locally for about 2 hours, then returned to land. The pilot stated that while in the traffic pattern preparing to land, the runway appeared to be in the same condition as during the departure. Instead, the runway was slush covered due to the morning sun melting the snow and the airplane veered to the left during landing rollout. The pilot was unable to maintain directional control and the airplane subsequently impacted a snowbank on the edge of the runway and nosed over, which damaged both wings and the vertical stabilizer.