import netCDF4

url='http://nomads.ncep.noaa.gov:9090/dods/rtofs/rtofs_global20140303/rtofs_glo_2ds_forecast_daily_prog'


nc = netCDF4.Dataset(url)

ncv = nc.variables

ncv['lon'][:10]

u = ncv['u_velocity'][0,0,0:100:3,0:100:3]
v = ncv['v_velocity'][0,0,0:100:3,0:100:3]
print shape(u)
print shape(v)