NOAA/PSL Catalog http://psl.noaa.gov/thredds/catalog/Datasets/dai_pdsi/catalog.html

Dataset Size Last Modified
     Folder  dai_pdsi   --
         Folder  old/   --
         pdsi.mon.mean.nc 51.71 Mbytes 2020-04-13T14:30:45Z
         pdsi.mon.mean.selfcalibrated.nc 62.74 Mbytes 2020-04-13T14:30:45Z

NOAA/PSL at NOAA PSL see Info
THREDDS Data Server [Version 4.6.15-SNAPSHOT - 2020-01-28T04:01:10+0000] Documentation