Where can I find sites for archived SYNOP, METAR, TAF data etc?
There are a growing number of sites that fit the bill: the ones listed below are simply a selection that I use routinely. Some will archive data for limited periods (say a month or less), others longer.
[ rolling archive of European SYNOP's ]
[ archive of METAR's, TAF's, SYNOP's etc., both coded & decoded ]
[ archive of coded data, including upper air ]