Rain improve receive?

Be willing to bet, if you check SWR when it's raining you'll find its threw the roof...I had a similar problem with my pick-up...when it rained I noticed the receive got real quite...checked SWR and it was pegging 3+... was loosing ground. ..had to make some changes to my antenna mount...Noticed yesterday when it was pouring again, no more problems.

 

While the scenario that JesseJames outlined could be correct, the exact opposite can be as well. By that i mean there may be an existing loose ground and the rain completes the grounding issue temporarily.

 

Depends on the mount, location of the antenna etc. What kind of truck? West coast mirrors ground can be improved by running a ground strap from the door to the cab to the frame.

 

It is mostly because the noise that is created by static electricity all around you and is absorb by the moisture from the rain - much of it is eliminated. You hear static electricity as atmospheric noise in the radio, seeing it is AM (or SSB), the noise is not filtered out and become part of the noise floor which can be as high as 20 over S9.

 

run a piece of 1/16 stainless steel cable from a shock mount bolt to where it barely drags the ground. Just like you see the tankers running rubber straps only us cable. Made a huge difference in my "white noise"

 

This also makes a great static ground to prevent a static discharge that can ignite a brush or stubble fire if you get offroad or into grain fields.

 

Sounds perfectly normal.
Enjoy while you can.