How to Read the Symbols and Colors on Weather Maps

meteteorologist in-training
H. Armstrong Roberts/ClassicStock/Archive Photos/ Getty

The weather map is a quintessential weather tool.

Much like how equations are the language of mathematics, weather maps are meant to convey a lot of weather information quickly and without using a lot of words. The easiest way to achieve this is by using weather symbols, so that anyone looking at a map can decipher the same exact information from it...  that is, if you know how to read it! Need an intro or refresher  to this? We've got you covered.

01
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Zulu, Z, and UTC Time on Weather Maps

UTC chart-vertical
A "Z Time" conversion chart for U.S. time zones. NOAA Jetstream School for Weather

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 time stamp. It tells you when the weather map was created and also when the weather data in it is valid for.

Known as Z time, this time is used 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.

02
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High and Low Air Pressure Centers

pressure centers wx map
High and low pressure centers are shown over the Pacific Ocean. NOAA Ocean Prediction Center

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.

Highs tend to bring clearing and stable weather, whereas lows encourage clouds and precipitation; so pressure centers are sort of "x-marks-the-spot" areas for 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.

03
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Isobars

weather map-isobars
NOAA Weather Prediction Center

On some weather maps you may notice lines surrounding and encircling the "highs" and "lows." These lines are called isobars because they connect areas where the air pressure is the same ("iso-" meaning equal and "-bar" meaning pressure). The more closely the isobars are spaced together, the stronger the pressure change (pressure gradient) is over a distance. On the other hand, widely-spaced isobars indicate a more gradual change in pressure.

Isobars are found ONLY on surface weather maps -- although not every surface map. Be careful not to mistake isobars for the many other lines that can appear on weather maps, like isotherms (lines of equal temperature)!

04
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Weather Fronts and Features

weather maps-front symbols
Weather front and weather feature symbols. adapted from NOAA NWS

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 red curved lines with red semi-circles.
  • Cold fronts are blue curved lines with blue triangles.
  • Stationary fronts have alternating sections of red curves with semi-circles and blue curves with triangles.
  • Occluded fronts are purple curved lines with both semicircles and triangles.

Weather fronts are found ONLY on surface weather maps.

05
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Surface Weather Station Plots

wx station model plot
A typical surface station weather plot. NOAA/NWS NCEP WPC

As seen here, some surface weather maps include groupings of numbers and symbols known as weather station plots. Station plots describe the weather at a station location, including reports of that location's...

  • air temperature (degrees Fahrenheit),
  • dewpoint temperature (degrees Fahrenheit),
  • current weather,
  • sky cover,
  • atmospheric pressure (in millibars),
  • pressure tendency, and
  • wind direction and speed (in knots).

If a weather map has already been analyzed, you'll find little use for the station plot data. But if you'll be analyzing a weather map by hand, station plot data is often the only information you start off with. Having all stations plotted on a map guides you as to where high and low pressure systems, fronts, and the like are located which ultimately helps you decide where to draw them in.

06
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Weather Map Symbols for Current Weather

station plot weather symbols
These symbols describe the current station plot weather. NOAA Jetstream School for Weather

These symbols are used in weather station plots. They tell what weather conditions are currently happening at that particular station location.

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

07
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Sky Cover Symbols

weather maps-cloud cover symbols
adapted from NOAA NWS Jetsream Online School for Weather

Sky cover symbols are used in station weather plots. The amount 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.

08
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Weather Map Symbols for Clouds

weather maps-cloud symbols
FAA

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.

09
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Wind Direction and Wind Speed Symbols

weather map-wind symbols
NOAA

Wind direction is indicated by the line that extends out from the station plot sky cover circle. The direction the line points is the direction that the wind is blowing from.

Wind speed is indicated by the shorter lines, called "barbs," which extend from this longer line. The total wind speed is determined by adding together the different sizes of barbs according to the following winds speeds that each represents:

  • Half barb = 5 knots
  • Long barb = 10 knots
  • Pennant (flag) = 50 knots 

Wind speed is measured in knots and is always rounded to the nearest 5 knots.

10
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Precipitation Areas and Symbols

weather map-radar
NOAA Weather Prediction Center

Some surface maps include a radar image overlay (called a radar composite) that depicts where precipitation is falling based on returns from a weather radar. The intensity of rain, snow, sleet, or hail is estimated based on color, where light blue represents light rain (or snow) and red/magenta indicates flooding rains and/or severe storms.

Weather Watch Box Colors

If precipitation is severe, watch boxes will also show up in addition to precipitation intensity.

  • Red dashed = tornado watch
  • Red solid = tornado warning
  • Yellow dashed = severe thunderstorm watch
  • Yellow solid = severe thunderstorm warning
  • Green = flash flood warning 
11
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Continue Your Weather Map Learning

Watercolour world map in soft colours
David Malan / Getty Images

Now that you've got reading surface weather charts down pat, why not try your hand at reading upper air forecast maps or these specialty weather maps and symbols used in flying and aviation.