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.01of 10
Zulu, Z, and UTC Time on Weather Maps
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 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 5:45 a.m. your time, that same day. (When reading the chart, note whether the time of year is daylight saving time or standard time and read accordingly.)02of 10
High and Low Air Pressure CentersHigh- and-low pressure centers are shown over the Pacific Ocean. NOAA Ocean Prediction Center
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.03of 10
IsobarsNOAA 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 has them. Be careful not to mistake isobars for the many other lines that can appear on weather maps, such as isotherms (lines of equal temperature).04of 10
Weather Fronts and Featuresadapted 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 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.05of 10
Surface Weather Station PlotsNOAA/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. They include reports of a variety of weather data at that location:
- Air temperature (in degrees Fahrenheit)
- Dewpoint temperature (degrees Fahrenheit)
- Current weather (marked as one of dozens of symbols established by National Oceanic and Atmospheric Administration or NOAA)
- Sky cover (also as one of NOAA's symbols)
- Atmospheric pressure (in millibars)
- Pressure tendency
- 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.06of 10
Weather Map Symbols for Current WeatherThese symbols describe the current station plot weather.
NOAA JetStream School for Weather
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
Adapted from NOAA NWS JetStream Online School for Weather
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.08of 10
Weather Map Symbols for CloudsFAA
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.09of 10
Wind Direction and Wind Speed SymbolsNOAA
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 from which the wind is blowing.
Wind speed is indicated by the shorter lines, called "barbs," which extend from the longer line. Wind speed is measured in knots (1 knot = 1.15 miles per hour) and is always rounded to the nearest 5 knots. 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
Precipitation Areas and SymbolsNOAA 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 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