If the parachute doesn’t open, or open correctly, you cut it away and deploy the reserve. The main parachute is packed by the owner; the reserve is packed by an FAA certificated rigger. Outside temp depends on altitude, time of year, location, etc. Currently the temp here in eastern NC at 24k feet MSL is -19C. I've seen it snow in August inside the aircraft when the tail gate is opened at 24k feet. A 90+ degree temperature difference between exit and landing isn't outside the norm.