“What kind of shorts do clouds wear?”/“Thunderwear.”

A popular children’s joke about the weather is:
 
Q: What kind of shorts do clouds wear?
A: Thunderwear.
 
The “thunderwear” joke has been cited in print since at least 1990. The joke has been printed on GIFs.
   
   
Google Books
Weather or Not:
Riddles for Rain and Shine
By Rick Walton, Ann Walton and Susan Slattery Burke
Minneapolis, MN: Lerner Publications Co.
1990
Pg. ?:
Q: What do clouds wear under their raincoats?
A: Thunderwear.
 
Google Groups: za.humour
Ozayr:JOKE4
UCT Student
3/3/99
What do clouds wear under their clothes?
Thunderwear.
 
Google Books
Kids’ Silliest Riddles
By Jacqueline Horsfall
Illustrated by Buck Jones
New York, NY: Sterling Publishing Company, Inc.
2003
Pg. 29:
What do rain clouds wear under their raincoats?
Thunderwear.
 
Google Groups: alt.humor.puns
Kids Puns of the Weak 09-21-04
Stan Kegel
9/21/04
(...)
What kind of shorts do clouds wear?
Thunderwear! (Rachel, 9)
     
Twitter
DMphotog
‏@DMphotog
What do clouds wear under their clothes?  Thunderwear!  #badjokes
9:10 AM - 6 Feb 2009
 
Google Books
Best Ever Classroom Jokes:
Because some of us never grow up
By Mike Haskins
New York, NY: Pavilion Books
2015
Pg. ?:
What kind of pants do clouds wear?
Thunderwear.
 
Twitter
Errol
‏@ErrolCeralvo
What kind of underwear do clouds wear? Thunderwear 🙂
11:28 PM - 22 Mar 2016