Does weather change that drastically over the duration of an average flight? Pilots get weather forecasts before take-off, are they inadequate? How does knowin

Does weather change that drastically over the duration of an average flight? Pilots get weather forecasts before take-off, are they inadequate? How does knowing the weather at the destination help with the immediate task of flying a plane through a thunderstorm that you knew was going to be there anyway and you can see on your radar? How more weather information change the impact of a major weather event e.g. East Coast winter storm, on air travel? I don't see how it could, the decisions are made far ahead of time because weather forecasts are pretty good.