Interesting point about gliders.
I remember back in the '70s when the first glassfibre sailplanes were coming along that a slope-soaring Kestrel 19 had to land out when a rain shower came along and reduced lift to such an extent that the aircraft could no longer maintain lift on the slope and was too low to complete a circuit to land (at Challock 1976).
The effect of rain on the performance of the laminar flow glassfibre wing was significant.
KR
FOK