The 'fringing' in jet stream cirrus, seen in the imagery, indicates the likelihood of severe turbulence.
13 July 2022
14 November 2013
As the jet stream propagates in a northeasterly direction towards Iceland, 'fringes', or bands of white cirrus cloud, can be seen across the flow. This cloud formation indicates the likelihood of severe turbulence in and near the cloud.
At this time Iceland issued warnings, and aircraft were reporting encountering severe turbulence.
Airmass RGB, 06:00 UTC, with 300 hPa isotachs overlaid (source: EUMeTrain)