I don't think it is, unless temperature stays constant or there is incoming source of water vapor. It reaches 100% when it is coldest in the night and all water

I don't think it is, unless temperature stays constant or there is incoming source of water vapor. It reaches 100% when it is coldest in the night and all water deposits down as frost (to provide exercise to people parking outside), then it warms up and the air is dryer. Bigger the temp swings drier the air outside. Applies to continental climate though, when you are near sea you probably have air constantly replaced with humid air.