There were lots of wind issues on Wednesday in DCA as well as weather/volume enroute up and down the east coast. This led to ATC holds and delays which resulted in several cancellations.

Also, keep in mind that US wasnt running a full Shuttle schedule for the holidays and 1/2 was the first day after the break so it is possible some aircraft may not have made it back into position due to issues elsewhere in the system.

Generally, the shuttle flights are pretty much on schedule. ATC holds are the biggest source of delays and cancellations - usually LGA flights. We do rotate in other aircraft at times when inbound shuttles are delayed.