O.K. a bit of info before getting to the topic. My wife and I are new hams....went onto the FCC ULS on 11/13/07...yes BRAND NEW.
I am currently using a Yaesu 8800, 2 meter/440, as a base station with a Comet GP 6 vertical antenna. The coax is a premade, ends on, and all is done right. The antenna connection is tightly taped and not exposed to the weather.
Heres the "kicker", initially I had an SWR reading of 1.5, during and after a light rain the SWR dropped to the point of barely moving the meter.
All components are matched and correct for one another, no corners cut.
Yes, a nice low SWR is great, but why would it change?