Low pressure
Also called low, cyclone, L on a map
Weather-map symbol. A chart convention, not a forecast icon.
Weather-map symbolsLow pressure meaning
Low pressure on a weather map is the letter L at a pressure center. NESDIS teaches it in red. The letter is the symbol, not the color.
At a glance
- System
- Synoptic chart convention
- Used for
- A low-pressure center
- Not the same as
- A rain icon or a front
An L for a low-pressure center. Not a rain icon, and not a cold front.
The name. The letter L is the mark. Red is a common aid. Storms are usual nearby, not spelled by the letter alone.
Where it comes from
NESDIS marks a low with a red L and says lows usually bring clouds and storms. The National Hurricane Center glossary names a red L as well. JetStream hangs fronts on lows: cold fronts typically to the south or west, warm fronts usually to the east. The L is the center. The fronts are the boundaries. Rain painted across a state is a third graphic.
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 is lower there than around it. The circulation and the fronts do the weather. Reading an L as “rain icon” skips the map’s grammar. A trough is lower pressure stretched into a line, and it is not given this letter.
Questions
What does L mean on a weather map?
A low-pressure center. NESDIS draws it red and associates lows with clouds and storms. Fronts are drawn separately, with triangles or half-moons.
Is a low the same as a hurricane symbol?
No. A low is the pressure center. Tropical-cyclone graphics are a further set and are not this letter.
Near this
- High pressureAn H for a high-pressure center. The letter is the symbol. Color is extra.
- Cold frontA line with triangles in the direction of motion. Cold air is advancing. The color is a publisher’s aid.
- Warm frontA line with half-moons in the direction of motion. Warmer air is advancing.
- TroughElongated lower pressure and a wind shift. Not a front. The dash is a common habit, not a second alphabet.
Sources
- NESDIS, how to read a weather map
- National Hurricane Center, USA glossary
- NOAA JetStream, surface weather maps
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.