The directories listed above contain GIF files with names of the form: yymmddhh_jetstream_anal.gif yymmddhh_jetstream_small.gif where yymmddhh is the UTC date and hour. In particular:

yy is the last two digits of the year;

mm is the month (a two digit number);

dd is the day of the month (a two digit number); and

hh is the hour of the day (a two digit number).