On a rainy day, we can hardly take the sun, so it causes melatonin released a lot. As a result, People can be blue. When we feel blue, our brain notices it and requires warm flour-based food. Protein and Vitamin B in flour is raise blood sugar in our body, so we feel better.
Another reason is some people have stomachache on a rainy day. Natural anti-diarrhea in spring onion can help them. It can be called "killing two birds with one stone" as eating delicious food and being healthy.