Warm front
Also called warm front symbol, red front, half moons
Weather-map symbol. A chart convention, not a forecast icon.
Weather-map symbolsWarm front meaning
A warm-front symbol is a line with half-moons pointing where the front is moving. NOAA lessons often draw it red. The half-moons are the mark.
At a glance
- System
- Synoptic chart convention
- Used for
- An advancing warm-air boundary
- Not the same as
- A cold front
A line with half-moons in the direction of motion. Warmer air is advancing.
The name. Half-moons on the side of motion. Red is the usual teaching color, not the shape.
Where it comes from
JetStream draws a warm front as a red line with half-moons in the direction of motion, usually east of the low. The half-moons point into the cooler air the warm air is overrunning. This drawing keeps the half-moons and drops the red, so the symbol still reads in gilt. A cold front’s triangles are the other ornament. Stationary and occluded fronts mix the two.
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
Warmer air is advancing. The weather ahead of it is often a wide cloud and precipitation shield, but the symbol does not draw that shield. Precipitation area, if the map paints one, is a separate convention. The front is the boundary.
Questions
What does a warm front look like on a map?
Half-moons on a line, on the side the front is moving. JetStream draws the line red and places the front usually east of the low.
Why not just use red for warm?
Color helps, and it fails in one ink and for some readers. The half-moon is the shape NOAA’s lesson pairs with the warm front.
Near this
- Cold frontA line with triangles in the direction of motion. Cold air is advancing. The color is a publisher’s aid.
- Stationary frontA front that is not moving. Ornaments sit on opposite sides of the line.
- Occluded frontA front that has caught up. Alternating triangles and half-moons share one side of the line.
- Low pressureAn L for a low-pressure center. Not a rain icon, and not a cold front.
Sources
Named when the entry depends on a text, a date, or a standard. Catalog numbers are not invented.
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symbol.wiki, edited as Sigilla. Last reviewed 18 October 2026. A reading of public tradition, not a ruling.