Bass are more likely to bite in the rain if it is a light rain. This is because light rain tends to make fish very active. In the early seasons rain can cause warming in the water which tends to make fish more active during this time. During the hot days of summer, rain can also be used to help cool the water down which often invokes species such as the largemouth bass to become more active.
When it rains it causes insects to inhabit areas around the water, as a result of this smaller fish that eat insects may thrive to these areas, thus drawing bass to the surface of the water as well, creating a feeding frenzy for all.
Another reason bass may be more attracted to thrive upon rainy days is because they are sensitive to light. Usually when it rains the sky darkens up a bit. Bass enjoy this and are also able to sense the change in wind and sky conditions causing them to feed more during this time. For this reason it has been said that some of the best fishing can be done when a cold front is approaching. The bass love to fill up on smaller fish, insects, etc. that come alive during a light rain.
When it begins to storm however, it usually will scare fish off and it is extremely hard during this time to try and entice a bass to bite an artificial lure. After this, the fish may be unwilling to eat for the next few days.
Still, some fishermen insist on continuing to try their luck at fishing during a storm. If you are still determined to do so, it is important to use the lightest line possible as well as the smallest lure possible. This should be practiced in order to not scare away the bass even more. Fishing can often prove to be difficult in muddy conditions as well as severe thunderstorms. It can also obviously bring more potential dangers.