As SFGate points out, it is possible to keep a regular refrigerator outside, although it may cost a little more to run and require additional maintenance. Standard refrigerators should not stay outside in extreme weather. Refrigerators specifically designed for outdoor use have the required weatherproofing and rust resistance.
If a refrigerator is being used outdoors in a location where electricity is not readily at hand, a generator is needed to power it. If the generator is turned off, the food in the refrigerator spoils easily. Place an outdoor refrigerator away from direct sunlight for better energy efficiency, and place it on blocks above the ground if there is any danger of flooding. Keep it dry to prevent rust, and clean the area around the pump frequently.
Standard refrigerators are not built to withstand extreme weather. In very humid or dry environments, the seals and gaskets around the door crack and break. In extremely cold temperatures, especially when it is below 0 degrees Fahrenheit, refrigerators are likely to stop working. In this situation, simply turn the refrigerator off, since the outside temperature is colder than that inside the refrigerator.
Outdoor refrigerators are typically made of stainless steel to withstand rust. They are also weatherproofed to remain safe in rain and other wet conditions. They are specifically designed to maintain a constant interior temperature no matter what the exterior weather is like.