If you don't protect these appliances and the power feeds from rain don't expect them to work for long. If excessive moisture gets into the control panel, especially on newer electronic controlled units, they will fail.
Would you leave your computer outdoors? Also remember the dryer is a 240VAC, 30amp unit and can light up your world if the the frame becomes hot, since I'm sure you don't plan on having GFIC protection on these units.
If you really have to use these outside, keep them covered well and unplugged when not in use, and keep the source power cords safe too.