Condensation from the car sitting for a period of time is burning off inside the exhaust. If you continue to have the issue after a few warm dry days then start to worry. Depends on how much "white smoke" your getting out. I once looked at a wagon for sale that had a lot of white smoke/steam. It didn't change after warming up a while. I found out the guy had been driving it with a broken thermostat and with the needle reaching the red. He held the coolant outtake hose going to the radiator and told me its never got hot before. Of coarse that was because no coolant was circulating. But the car had a large plume of steam looking smoke.

My two wagons like to spit a little bit of drops out. One more than the other for sure.