Forget leaves on the line, or the wrong kind of snow. Transport for London has a far more serious problem: there are severe delays on the Piccadilly line, thanks to a shortage of staff.
Passengers have been advised to avoid using the line completely if at all possible.
TfL said there was a "shortage of train operators," which has resulted in severe delays across the whole line, and partial closures. At the moment, the line is closed completely between Cockfosters and Uxbridge.
TfL said customers' tickets will be accepted on the local buses and Great Northern train services instead.
The delays have been going on all day. TfL's first tweet alerting passengers to severe delays on the line due to a "temporary lack" of operators was 20 hours ago, just after 8pm last night. The situation was exacerbated by ice on the line earlier today.