This is the final installment of the synoptic meteorology series which will help you read and understand weather maps:
Surface Weather Plots
A complete surface weather station plot.
On some surface maps you will see station weather plots. Since meteorologists must convey a lot of information without using a lot of words, these plots are used to describe the weather at a station for a specific time. When all stations are plotted on a map, a “picture” of where the high- and low-pressure areas are located, as well as the location of fronts, can be obtained.
There are a large number of weather symbols used for station plotting. Some are used for weather elements such as rain, snow, and lightning. Others represent the speed of the wind, types of clouds, air temperature, and air pressure. All of these symbols help meteorologists depict the weather occurring at a weather observing station.
This sample plot represents the maximum amount of information about the current weather at an observing station. Hand plotted maps usually contain the full weather information. However, nowadays it is rare to see the full plot as most computer-generated surface weather maps omit some data such as clouds types, cloud heights and past weather.
Before computers, the plotting of weather maps was considered an art. In fact, Aerographers (weathermen) in the U.S. Navy continue to plots maps by hand. A skilled plotter can easily fit the above information under the space covered by a dime.
Decoding these plots is easier than it may seem. The values are located in a form similar to a tic-tac-toe pattern. Print key. (pdf)
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In the upper left, the temperature is plotted in Fahrenheit. In this example, the temperature is 77°F. |
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Along the center, the cloud types are indicated. These cloud types use the same cloud codes as found in the cloud chart section. The top symbol is the high-level cloud type followed by the mid-level cloud type. The lowest symbol represents low-level cloud over a number which tells the height of the base of that cloud (in hundreds of feet) In this example, the high-level cloud is Cirrus, the mid-level cloud is Altocumulus and the low-level clouds is a cumulonimbus with a base height of 2000 feet. [more on these symbols] |
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At the upper right is the atmospheric pressure reduced to mean sea level in millibars (mb) to the nearest tenth with the leading 9 or 10 omitted. In this case the pressure would be 999.8 mb. If the pressure was plotted as 024 it would be 1002.4 mb. When trying to determine whether to add a 9 or 10 use the number that will give you a value closest to 1000 mb. |
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On the second row, the far-left number is the visibility in miles. In this example, the visibility is 5 miles. |
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Next to the visibility is the present weather symbol. There 95 symbols which represent the weather that is either presently occurring or has ended within the previous hour. In this example, a light rain shower was occurring at the time of the observation. [See all the symbols] |
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The circle symbol in the center represents the amount of total cloud cover reported in eighths. This cloud cover includes all low, middle, and high-level clouds. In this example, 7/8th of the sky was covered with clouds. [see the complete list of symbols] |
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This number and symbol tell how much the pressure has changed (in tenths of millibars) in the past three hours and the trend in the change of the pressure during that same period. In this example, the pressure was steady then fell (lowered) becoming 0.3 millibars LOWER than it was three hours ago. [see all pressure tendency symbols] |
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These lines indicate wind direction and speed rounded to the nearest 5 knots. The longest line, extending from the sky cover plot, points in the direction that the wind is blowing FROM. Thus, in this case, the wind is blowing FROM the southwest. The shorter lines, called barbs, indicate the wind speed in knots (kt). The speed of the wind is determined by the barbs. Each long barb represents 10 kt with short barbs representing 5 kt. In this example, the station plot contains two long barbs so the wind speed is 20 kt, or about 24 mph. [more about wind barbs] |
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The “71” at the lower left is the dew point temperature. The dew point temperature is the temperature the air would have to cool to become saturated, or in other words reach a relative humidity of 100%. |
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The lower right area is reserved for the past weather, which is the most significant weather that has occurred within the past six hours excluding the most recent hour. [see the complete past weather symbols] |
Analyzing Weather Maps
Once you can read a station plot you can begin to perform map analyses. Meteorologists use the station plots to draw lines of constant pressure (isobars), temperature (isotherms), and dew point (isodrosotherms) to achieve an understanding of the current state of the atmosphere. This knowledge ultimately leads to better weather forecasts and warnings.
It felt like a typical Fall weekend just a tad cooler. We had hail here yesterday. Today was dry. Thanks for all the info this past week MV, great post yesterday Slim. I notice around here some trees are brilliant and some have lost their leaves.
I still find it interesting how so many leaves are on the trees with all of the cool weather we have been experiencing lately. I would assume the rainy year is a big factor in keeping them staying around longer.
P.S. I am really excited for the first big snow, but I will keep my hype down until it happens.
Good morning. Yesterday Grand Rapids seen a mix of weather conditions. There was some sun (not much) several heavy hail/snow/rain showers some on the hail/snow showers had light acclamations here at my house. The H/L was 43/35, there was 0.33” of total precip with a T of snow fall at GRR. For today the average H/L is 53/37. The record high is 76 set in 2015 and the record low is 17 set in 1951. The record snow fall amount is 10.4” in 1991. That year the high of November 3rd was just 23 and of course we had a… Read more »
A ton of good info the past week MV! I’m kind of nervous for the test. Ha
The test is tomorrow – I made a page with much of the info under the MIReady menu/Synoptic Meteorology
Current 32* degrees out at thee YARDofBRICKS NE of GR we had about 3 hours of wet snow last night it was great and we have more on thr way tonight already off to a cool start to November I believe this will be our 6th day in roll below normal keep the furnace running winter coats and hats on have a super Sunday….INDY