Trough
Also called surface trough, trof, dashed line
Weather-map symbol. A chart convention, not a forecast icon.
Weather-map symbolsTrough meaning
A trough on a weather map is an elongated area of lower pressure, with a wind shift, and JetStream says it is not an air-mass boundary.
At a glance
- System
- Synoptic chart convention
- Used for
- Elongated lower pressure
- Not the same as
- A cold front or a low
Elongated lower pressure and a wind shift. Not a front. The dash is a common habit, not a second alphabet.
The name. An elongated area of lower pressure. JetStream says it is not an air-mass boundary.
Where it comes from
NOAA’s JetStream lesson defines a trough as elongated lower pressure and a wind shift, and it says the trough is not an air-mass boundary. Fronts are the boundaries, with triangles or half-moons. Charts often draw a trough as a dashed line. The dash in this cabinet is that common habit, so the page has a shape. It is not a claim of one international dash pattern. A low is the closed center. A trough can extend from it.
The line drawing is original to this cabinet. It is not an agency logo, a vendor icon, or the emoji for the same idea.
Weather
What it means
Pressure sags along a line, and the wind shifts across it. There may be weather. There may not be a front. If you need the air-mass change, look for triangles, half-moons, or the legend. The dashed line alone, without a legend, should be read cautiously. This page tells you the concept the word means in that NOAA lesson.
Questions
What is a trough symbol?
A trough is elongated lower pressure and a wind shift. JetStream is explicit that it is not an air-mass boundary. Dashed lines are a common way to draw one. The dash is not, by itself, a second official alphabet.
How is a trough different from a front?
Fronts carry triangles or half-moons and mark air-mass boundaries. A trough marks a pressure shape and a wind shift.
Near this
- RidgeElongated higher pressure. The zigzag is a reading aid, not a WMO code.
- Low pressureAn L for a low-pressure center. Not a rain icon, and not a cold front.
- Cold frontA line with triangles in the direction of motion. Cold air is advancing. The color is a publisher’s aid.
- IsobarA line joining equal pressure. The number is the pressure. The line is not a front.
Sources
Named when the entry depends on a text, a date, or a standard. Catalog numbers are not invented.
Your margin
Private. It stays in this browser and never joins the canon.
symbol.wiki, edited as Sigilla. Last reviewed 18 October 2026. A reading of public tradition, not a ruling.