Through lines pseudo fronts

Trough line are elongated area of relatively lower pressure, often without a strong temperature contrast like a front represented by orange barbed lines with barbs pointing toward the pressure fall side.

Through line overs France, 14 August 2025

The orange barbs are heading towards left and right. 

So how this differs from an occluded front with blue triangles and red circles alternating in purple colours?

A trough line as in the above picture represents an elongated area of relatively lower pressure (T), often without a strong temperature contrast like a front. In many ECMWF-derived synoptic charts orange lines with short barbs are pointing toward the pressure fall side.

Weather meaning:

• Often the focus for showers or thunderstorms, especially in warm, humid air.
• Less organised than a front, the change in temperature, wind, and pressure can be subtle until the convection starts.
• Can trigger squalls if embedded in unstable air, particularly over warm seas.
• For sailors in the Adriatic: a trough line moving over warm summer waters can be the spark for sudden thunderstorms or gust fronts, even if the general synoptic pattern looks calm.
• Can be tied to a Nevera in the Adriatic, including the type that hit Rovinj/Šibenic in June 2025.

Sailors meaning:

• the the ambush predator → sudden, violent, short-lived; 
• often summer thunderstorms; 
• ambush predator → sudden, violent, short-lived.