Fog is quite frequent on Zagreb-Ljubljana road (mostly proper highway, finally). I had some memorable night drives there myself. Should you choose air transport, today it would be A320 (or ATR42, worst case )
Let me know if your plans firm up!
Cheers!
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Dragi "Bonzi" Raos
Q#5196
MkII #080000376, 18GB green
MkIIa #040103247, 60GB blue