2003 Chevy Astro won't start on rainy days

Hi:
The most common cause is plug wires. Has the check engine light ever come on?

Here is an easy way to check the plug wires. When it's dark, open the hood to see if you can see if there are any archs shorting from the plug wires. If not, take a spray bottle and mist the wires to see if the begin to short.

Let me know what you find.
Joe