In my experience there are two things that cause car doors to freeze shut in extreme cold: one is rain (or wet, melting snow) followed by extreme cold and wind. The other is washing your car, and parking it soon afterward and then a big temperature drop.

The 'carwash freeze' is the worst, and all doors and windows and trunk could be compromised. You might have to pick a door and pry it open with a wooden shim. This can be avoided by driving the car for 20 miles or so with the heater on before parking.

The rain/freeze can be mitigated somewhat by parking the car in the sun so only one side faces the prevailing wind. The other side will not freeze.