NOAA/ESRL/PSD Catalog http://www.esrl.noaa.gov/psd/thredds/catalog/Datasets/dai_pdsi/catalog.html

Dataset Size Last Modified
     Folder  dai_pdsi   --
         Folder  old/   --
         pdsi.mon.mean.nc 51.71 Mbytes 2016-04-06T14:11:40Z
         pdsi.mon.mean.selfcalibrated.nc 62.74 Mbytes 2016-10-28T20:30:25Z

NOAA/ESRL/PSD at NOAA ESRL PSD see Info
THREDDS Data Server [Version 4.3.15 - 20121218.1126] Documentation