Add a reasonable time range.  Can probably be improved by actually checking masked data.
Add a reasonable time range.  Can probably be improved by actually checking masked data.

git-svn-id: acf0ef94bfce630b1a882387fc03ab8593ec6522@89 150532fb-1d5b-0410-a8ab-efec50f980d4

deeplycloudy/MetPy,dopplershift/MetPy,ahaberlie/MetPy,ahaberlie/MetPy,Unidata/MetPy,dopplershift/MetPy,Unidata/MetPy,jrleeman/MetPy,jrleeman/MetPy,ShawnMurd/MetPy,ahill818/MetPy