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Surface Map Help Page

This product is one of many graphical products used in meteorology. The surface map is created to show the general pattern of the weather occuring across the country at a certain time. As the name would lend itself to, a surface map shows what is going on at the surface (ground level). On a surface map many things are plotted and displayed.

Typical surface map used in meteorology

1) Station Data Plot
White circles with stick coming out of them with green numbers surrounding them



Example of a station data plot


White Circle: Indication of fraction of cloud coverage (in fourths) at a given location.
Example: If circle is completly white, then the weather at that station is overcast.

Stick: Represents the wind direction and speed at the station.

Direction: Stick points to bottom of map = wind from the south; Stick points to left of map = wind from the west; Stick points to top of map = wind from the north; Stick points to right of map = wind from the east
Speed Wind speed is determined by the number and length of lines coming out of the end of the stick.: Short line = 5 mph (miles per hour); Long line = 10 mph; Triangle = 50 mph
Green Numbers: The three numbers on the station plot represent the TEMPERATURE (upper left number), the DEWPOINT, and the PRESSURE number (right number).

The pressure number is in millibars and if the first number is 9, then the pressure is just the number given.

Example: number is 997, pressure is 997 millibars

if first number is 0 or 1, then you need to add 1000 to FIRST TWO numbers and then place decimal.

Example: number is 162, then the pressure is 1016.2 millibars.


2) High Pressure (H), Low Pressure (L), and Pressure Lines
On the surface map you will find the High Pressure areas and Low Pressure areas and their respective pressure values.

High Pressure
marked with a blue 'H'
Fair Weather

Low Pressure
marked with a red ' L '
Stormy weather

Pressure Lines
On the surface map you will also find contoured pressure lines (white)
These lines point out where areas of identical pressure values are located.


3) Fronts, Trofs, and Dry-Lines

Cold Fronts, marked with a blue line on the map
Warm Fronts, marked with a red line on the map
Stationary Fronts, marked with alternating red and blue line on the map
Occluded Fronts, marked with a purple line on the map

For more information on fronts, check out this page.

Trofs, marked with a yellow dashed line on the map
Dry lines, marked with a brown dashed line on the map


4) Severe Watch Boxes
If there have been either Tornado or Severe Thunderstorm Watches issued recently they will show up on the map outlined by a green polygon. In the polygon will be two things: Type of watch issued and the time it is valid until.

Type of Watch
The watches that are shown on this surface map are either of the severe thunderstorm or tornado variety. The way to tell the two apart on the map is to look for the leading letter in the first line of code in the watch box. If the leading letter is a S, then you are dealing with a severe thunderstorm watch. If the leading letter is a T, then what you have is a tornado watch.

Expiration Time
All watches on this map have expiration times given in Zulu Time. Usually severe weather watches have a "lifetime" of about five hours.



Here is an example of a watch on the surface map. This is a severe thunderstorm watch, note the S, issued for northern Wyoming and southern Montana until 4Z (11 PM CDT).
Helpful Questions and Answers:

What should we look for on a surface map to help us predict severe weather?
On a surface map, we should first look and see if there are any fronts (cold, warm, or stationary) on the map. Fronts are good lifting mechanisms for air and storms can usually be found near or ahead of a front. Drylines are depicted by a dashed yellow line and can also be a good indicator of severe weather because it shows where a sharp moisture gradient is occurring.