We used to have occasional problems on the 135 after engine washes. If the wash is carried out with engines not running then during the drying run the heater is switched on. This would then waft a gentle flow of nice hot, very moist air over the cool screens; instant fog on the insides!
If we got a job immediately after the wash then it was not unusual to go IMC for half a minute just after takeoff!
TeeS