https://www.autorouter.aero/wiki/gramet/

Areas where there are strong winds are surrounded by brown lines, called isotachs. These lines are made up of alternating dashes and dots and the combination of the two specifies what they mean. Strong winds are winds of at least 25 knots. A dash and one or more dots show strong wind is in 25 knots increments. A dash and a single dot signifies 25 knots, a dash followed by two dots 50 knots and a dash followed by 3 dots 75 knots.

Perfekt, danke!