Download Correct Wind Data

Regardless of how we read wind data into the program, we're going to need to have a simple method for downloading data and storing it.  Using the gribfilter sheaff showed us in class (http://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_hd.pl?dir=%2Fgfs.2013102300%2Fmaster) let's figure out how to determine the correct file to download, given a launch time, and build some scripts to automate that.
