I have had the wonderful opportunity to experience this myself, back in 2004. I was flying as a pax from Athens, Greece, to Milan, Italy on Alitalia. It had just snowed in Athens, the airport was unprepared, and there was little to no available de-ice fluid. It was some variant of the DC-9/MD-88 etc. and I was sitting aft of the right wing, just like this guy. A couple of inches of slushy wet snow were on the wing, and away we went.

I'm pretty sure I held my breath until I was blue in the face.