Two pieces of direct evidence in support of Phil's comments:
1. Shot a surprisingly good image in 99.9% RH (even managed to avoid dew problems
). The local air temp was 19C, so the moisture loading was very high. SQL 20.8. From the subs, seeing was ~2.5" - a little better than average for the venue.
2. Had a perfect looking night - low RH, 21+ SQL - ruined by what proved to be high level smoke haze which was not obvious at the start of the run and escaped detection by my RH and SQL monitors (I don't have a cloud sensor).
The only solution I can see for the second example is to be there watching the subs deteriorate. (I WAS there, but not watching
)
Mark