How to Read the Symbols and Colors on Weather Maps

Tiffany Means is a meteorologist and member of the American Meteorological Society who has worked for CNN, the National Oceanic and Atmospheric Administration, and more.

A weather map and its symbols are meant to convey a lot of weather information quickly and without using a lot of words. Just as equations are the language of mathematics, weather symbols are the language of weather, so that anyone looking at a map should be able to decipher the same exact information from it. that is, if you know how to read it. Here is an introduction to weather maps and their symbols.

Zulu, Z, and UTC Time on Weather Maps

One of the first coded pieces of data you might notice on a weather map is a 4-digit number followed by the letters "Z" or "UTC." Usually found at the map's top or bottom corner, this string of numbers and letters is a timestamp. It tells you when the weather map was created and also the time when the weather data in the map is valid.

Known as Zulu or Z time, this figure is included on a weather map so that all meteorological weather observations (taken at different locations and therefore, in different time zones) can be reported at the same standardized times no matter what the local time might be.

If you're new to Z time, using a conversion chart (like the one shown above) will help you easily convert between it and your local time. If you're in California (which is Pacific Coastal Time) and the UTC issue time is "1345Z" (or 1:45 p.m.), then you know that the map was constructed at 6:45 a.m. your time, that same day (5:45am when daylight saving time is in effect). When reading the chart, it's important to note whether the time of year is daylight saving time (DST)—which is never has DST—or standard time and read accordingly.

High and Low Air Pressure Centers

The large letters (Blue H's and red L's) on weather maps indicate high- and low-pressure centers. They mark where the air pressure is highest and lowest relative to the surrounding air and are often labeled with a three- or four-digit pressure reading in millibars.

Highs tend to bring clearing and stable weather, whereas lows encourage clouds and precipitation. So pressure centers are "x-marks-the-spot" areas to aid in determining where these two general conditions will occur.

Pressure centers are always marked on surface weather maps. They can also appear on upper air maps.

Isobars

Weather fronts appear as different colored lines that extend outward from the pressure center. They mark the boundary where two opposite air masses meet.

• Warm fronts are indicated by curved red lines with red semicircles.
• Cold fronts are curved blue lines with blue triangles.
• Stationary fronts have alternating sections of red curves with semicircles and blue curves with triangles.
• Occluded fronts are curved purple lines with both semicircles and triangles.

Weather fronts are found only on surface weather maps.

Surface Weather Station Plots

These symbols were established by NOAA for use in weather station plots. They tell what weather conditions are currently happening at that particular station location.

These symbols are typically only plotted if some type of precipitation is occurring or some weather event is causing reduced visibility at the time of observation.

Sky Cover Symbols

NOAA has also established sky cover symbols to use in station weather plots. In general, the percentage that the circle is filled represents the amount of sky that's covered with clouds.

The terminology used to describe cloud coverage—"few," "scattered," "broken," "overcast"—are also used in weather forecasts.

Weather Map Symbols for Clouds

Now defunct, cloud type symbols were once used in weather station plots to indicate the cloud type(s) observed at a particular station location.

Each cloud symbol is labeled with an H, M, or L for the level (high, middle, or low) where it lives in the atmosphere. The numbers 1–9 tell the priority of the cloud reported. Since there's only room to plot one cloud per level, if more than one cloud type is seen, only the cloud with the highest number priority (9 being highest) is plotted.