Alyson Hannigan (Lily) was pregnant with her first child, and wears baggy clothes or is shot from the chest up throughout the episode.
The title of this episode is a play on the title of the Pulitzer Prize-nominated Richard Greenberg play "Three Days of Rain."
The old lady sat next to Lily on the plane also appeared as the wig lady in "double meat palace", the season 6 episode of Buffy the Vampire Slayer in which Alyson Hannigan played series regular Willow.
The scene, in which Ted and Barney mixing drinks in MacLaren's bar while 'Kokomo' from Beach Boys is playing is a reference to the Tom Cruise movie, titled 'Cocktail'.
The patch on Ted's arm is a brand logo for the EVER clothing company; this logo appears several times through the series.