99 Corolla CE auto does not start after sitting in rain/snow

Hi,

I have a very weird problem in my Corolla (99 CE auto 72 K miles): If my car sits in the rain for more than few hours than engine does not start just crank. Once the rain is stopped and weather becomes dry than engine starts only after jump-starting. After than it runs fine until next rain. I will highly appreciate any kind of help. Thanks.