Does the national flag law stipulate that the national flag should be raised in bad weather?

Yes, the specific provisions are: if the national flag should be hoisted, it should not be hoisted in bad weather.

Attachment: People's Republic of China (PRC) National Flag Law

Article 12

Where the national flag is hoisted in accordance with the provisions of Articles 5, 6 and 7 of this Law, it shall be hoisted in the morning and lowered in the evening.

If the national flag should be hoisted in accordance with the provisions of this law, it may not be hoisted in case of bad weather.