“When thunder roars, go indoors”

“You see, whenever thunder roars, most everybody runs indoors” was cited in print in 1933 and has been long-known advice, on Tornado Alley and elsewhere. The U.S. National Weather Service (National Oceanic and Atmospheric Administration) first used the “When Thunder Roars, Go Indoors!” slogan in 2005 and has used it annually since then.
 
The saying is sometimes worded as “When thunder roars, stay indoors” or “When thunder roars, get/head indoors.”
 
 
National Weather Service (National Oceanic and Atmospheric Administration)
Lightning Risk Reduction Outdoors
When Thunder Roars, Go Indoors!
There is little you can do to substantially reduce your risk if you are outside in a thunderstorm. The only completely safe action is to get inside a safe building or vehicle.
   
13 November 1933, The State-Times (Baton Rouge, LA), “The Tiny Mites” by Hal Cochran, pg. 14, col. 1:
“You see, whenever thunder roars, most everybody runs indoors.”
(Spoken by “The Thunder Man”—ed.)
 
Google Books
Aware: warning coordination and hazard awareness report
United States. National Weather Service.; United States. National Oceanic and Atmospheric Administration.
Washington, DC: U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration
2005
Pg. 21:
The team’s new slogan, When Thunder Roars Go Indoors, features Leon the Lion as its mascot.
 
OCLC WorldCat record
When thunder roars—go indoors!
Author: R Blumenthal
Edition/Format: Article : English
Publication: South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde, 2006 Jan; 96(1): 38-9
Database: From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
Other Databases: ArticleFirst
 
OCLC WorldCat record 
When thunder roars, go indoors : lightning safety.
Author: Betty Debnam
Publisher: [USA] : Universal Press Syndicate, ©2006.
Series: Mini pages
Edition/Format: Book : English
 
OCLC WorldCat record
Lighting[sic]/thunderstorms : when thunder roars, go indoors.<

Author: North Dakota. Department of Emergency Services.
Publisher: [Bismarck, N.D.] : North Dakota Dept. of Emergency Services, [2009]
Series: Severe summer weather
Edition/Format: eBook : Document : State or province government publication : English
 
OCLC WorldCat record
Lightning safety and preparedness : when thunder roars, go indoors!
Author: Canada. Environment Canada.
Publisher: [Ottawa] : Environment Canada, ©2012.
Edition/Format: eBook : Document : National government publication : English

Federal Emergency Management Agency (FEMA)
When Thunder Roars, Go Indoors!
Release date: June 26, 2013.
PORTSMOUTH, N.H.—Thunderstorms and lightning are in the forecast for much of New England this week. To be safe from dangerous lightning follow this simple rule: When thunder roars, go indoors.
 
Lightning kills an average of 55-60 people a year in the U.S. But 90 percent of those who are struck survive, often with permanent neurological disabilities. Eighty percent of lightning fatalities occur among men who were fishing, boating, golfing, biking, or working outdoors.