Question about the book "Significant tornadoes" and it's ratings on tornadoes.

[MatthewCarman]

I was looking through the "Significant tornadoes" update book and noticed something I don't understand. On June 19, 1993 a tornado touched down in near Dubuque, Iowa and moved through NW Illinois ending near Grant, Wisconsin. Now the book has it listed as an F1 tornado but at the end of the description is says "Officially F3". I noticed other tornadoes with two ratings and I don't know which one to go by. Now I did look through the introduction for an answer but never found one. Is the F1 rating unofficial and why is it used? Any answers to my question is apreciated. Thanks.

 

[Bob Hartig]

Grazulis's F-scale ratings occasionally differ from the official NWS ratings. Read the second paragraph on page iii in the Introduction regarding the use of italicized descriptions. You'll note that the entry for the storm you've mentioned was italicized per the convention set in the original, much larger volume. Grazulis felt that this storm didn't fulfill F3 criteria and assigned it his own rating of an F1.

 

[MatthewCarman]

Thanks Bob, now I know where to look in the book for information on the two ratings. I apreciate the help.