Change the weather is good today to a double negative sentence

The weather won't be bad today.

It will not fail to apply two negative words, which has a more positive meaning, that is to say, the weather today must be good, and the emphasis is stronger.

Double negative sentence refers to a sentence pattern that is negative twice to express a positive meaning. The tone of double negative sentences is stronger than that of affirmative sentences, which has an undoubted affirmative effect and strengthens the affirmative effect. Double negative words include "can't not", "don't not", "not not", "can't not", "have to", etc.