In most cases fair weather fans are bandwagoners who join in on the hype of a team or sporting event. Examples of this are: The Superbowl, The World Series, and Playoffs in general.
In other cases fair weather fans are people who just watch the sport or certain games when 'the weather is right'(when they feel like it). These fans are not characterized as bandwagoners because they have been fans of the sport/team before the hype and or big game (ex. Superbowl).
This is an example of a fair weather fan that is also a bandwagoner:
My brother: The World Series on tonight! I can't wait!
Me: Since when did you like baseball?
My brother: I don't, but its the World Series!
This is an example of a fair weather fan:
My friend: Celtics are on tonight.
Me: Since when do you watch basketball?
My friend: I watch it occasionally, plus its the playoffs.
Regular fan: "How would you know? You left right when Favre threw the pick six in the 2nd and if I recall you didn't even start rooting for Green Bay until 2 weeks ago."
Fair weather fan: "... GO PACK!"
(After the playoff game the fair weather fan immediately became a Pats fan and stowed all Packer memorabilia away.)
Fair Weather Fan's creed:
Last to join, first to leave.
Who Dat: it is Stand up and get Crunk
Who Dat 2: who in the fuck is that?
Who Dat: Another fucking New Dat
Who Dat2: Where were all of them 8 weeks ago?
Who Dat: Leaching of the corndogs at LSU. Don't worry they won't be here long.
Who Dat 2: Good I hate the fair weather fans, they are fucking useless and they are raising the ticket prices.
"Georgia (Bulldogs) are the opposite of fair weather fans, they are DAWGS to the core, win or lose."
Most often the term is used incorrectly to describe a fan who is extremely critical of their team during unsuccessful periods.
His favorite team didn't Slang That Eppley so he is pulling for someone new today.