The vote-to-close privilege page on Super User states the following (emphasis added):
You may cast up to 24 close votes per day. (This ceiling increases dependent on your flag weight and is set at a default of 50 on Stack Overflow.)
How does this limit increase as my flag weight increases? I haven't received more than 24 votes to close in spite of a high flag weight on SU (673.8296 as of the time of this post).