NorthAviMet, the best source for NAMcon countries - Denmark, Estonia, Finland, Iceland, Latvia, Norway and Sweden, requires a Login which is granted upon request for pilots expressing interest to fly there.
Weatheronline or
Wetterzentrale Topkarten the comprehensive access to data for weather calculations with all common models including GFS (US), ECMWF (European), WRF and ICON (German), HIRLAM (Dutch), ARPEGE (French) and GEM (Canadian). Requires to build up some interpretation skills, as the flood of information may look confusing at first.