LORELAI: They’re snowed in.
SOOKIE: Who’s snowed in?
LORELAI: The Bracebridge group. They’re stuck in Chicago. The dinner’s off.
In real life, December 2001 was warmer than average in Chicago, and it only snowed once, which took place close to Christmas, after the events of this episode.
The writer, Daniel Palladino, must have been thinking of the previous year – there was a terrible blizzard on Tuesday December 11 which raged for hours, with very heavy snowfalls. The storms continued on and off for the rest of the month, making it one of the heaviest snowfalls of all time for the city, an entire season’s worth.
Not being psychic, of course Palladino could only refer to a past blizzard, he didn’t know what the weather would be like in the upcoming December.
(The picture shows a plane grounded at O’Hare Airport in December 2000; flights really were cancelled).
The Annotated Gilmore Girls 