Methods of weather forecasting and navigation in the N-Atlantic in the Middle Ages tested with a modern NWP tool

Weather forecasting in the Middle Ages was most likely mostly based on persistence, and there are indications that persistence and correlation between elements of the sensible weather, in particular fog, helped in navigation in the N-Atlantic during the Viking age.

Investigation of the weather in the CARRA dataset, produced by dynamic downscaling, reveals that the connection between wind directions and fog is different on the leg between Iceland and Greenland from what it is between Iceland and Norway.  Consequently, the same navigational rules could not be applied on both these legs, making navigation from Iceland to Greenland even more difficult than navigation from Norway to Iceland.  This, in addition to very high frequency of fog and of strong winds in the vicinity of Greenland, made sailing and navigation between Iceland and the Medieval Nordic settlements in Greenland exceptionally difficult.