For the period 2011-04-22 to 2011-06-06, this directory is missing
KVNX2011051308.tar through KVNX2011051309.tar, KVNX2011052614.tar, 
and KVNX2011060213.tar through KVNX2011060215.tar (6 files total).
NCDC did not include these files in the order and they are presumed
unavailable.