9.2: Synoptic Weather Maps

The Station Model

Surface weather observations from many weather stations at a given time can be shown on a weather map using a station plot model, as shown in Figure 9.2.1. Station plot models typically display wind information via wind barbs, along with current weather conditions, sea-level pressure, temperature, dew point, visibility, and cloud cover. Sometimes, additional information, such as pressure tendency, cloud type, and precipitation amounts, is also provided.

Figure \(\PageIndex{1}\): Diagram illustrating a standard meteorological station model used on weather maps. Labels identify each element of the station model and explain how multiple weather variables are encoded in a compact visual format for meteorological analysis. (Public Domain; The station plot via NOAA).

As illustrated in \(\PageIndex{1}\), the top left number 57 in the station model example indicates the current air temperature at the station's location in Fahrenheit (F). Similarly, the bottom-left number 56 indicates the dew point, the top-right number 107 indicates the sea-level pressure, and the bottom-right number -6 indicates the pressure trend. Additional symbols and numbers indicate current weather conditions and recent pressure changes.

At sea level, average pressure typically ranges from 950 to 1050 mb (millibars). With a decimal point, this can require four or five digits to be displayed. Instead, the station model abbreviates the pressure to three decimal places, with the last digit indicating the nearest tenth. The initial 9 or 10 is also left out. Thus, when a reading station models pressure, first place a decimal point to the left of the third (last) digit. If the three-digit number is less than 500, then a 10 is placed to the left of the number. If the three-digit number is greater than 500, then a 9 is placed to the left. So, “147” is actually 1014.7 mb, and “998” would be 999.8 mb.

Just below the sea-level pressure value is the pressure trend, measured in mb. It has two components: a number and a symbol to indicate how much (in tenths of millibars) the pressure changed over the past 3 hours and the trend in that change. In \(\PageIndex{1}\), the pressure decreased by 6 mb and then became steady at the current value. Table \(\PageIndex{1}\) shows the meanings of the different pressure trend symbols.

Table \(\PageIndex{1}\): Pressure trend symbols and their meanings.

Symbol	Meaning
	Steady
	Continuously Rising
	Continuously Falling
	Rising, then steady
	Falling, then steady
	Rising after slightly falling
	Rising, then slowly falling
	Falling after slightly rising
	Falling, then slowly rising

A barbed line extending from the station model's central circle represents wind, with its orientation and markings indicating wind direction and speed. When reading wind barbs, keep in mind that the flag always points in the direction that the wind is coming from. You can think of it as an arrow flying from a bow; the flag represents the feathers, which are at the back of the arrow in the direction the arrow is coming from. The tip is the direction the arrow is flying toward. The barbs on the pole indicate wind speed. Table \(\PageIndex{2}\) illustrates what each wind barb symbol represents. The total wind speed is calculated by adding all the barbs and pennants. On many weather maps, wind speeds are given in knots, though different maps may use different units, so it is always good to check.

Table \(\PageIndex{2}\): Wind barb table illustrating the symbols used to denote wind speeds.

Symbol	Wind speed	Description
	Calm	two concentric circles
	1 - 2 knots	a line with no barbs
	5 knots	a half barb
	10 knots	a full barb
	50 knots	a pennant (triangle)

The center symbol indicates cloud cover, and Table \(\PageIndex{3}\) links numerical sky-cover values measured in Oktas (eighths) to standardized sky-cover categories, abbreviations, and equivalent tenths of sky coverage. Categories range from clear sky to overcast conditions, through few clouds, scattered clouds, and broken clouds. An additional row describes cases in which the sky is obscured or not measured. Each category is paired with its corresponding circular symbol used on weather maps, enabling users to interpret sky-cover information from plotted station observations.

Table \(\PageIndex{3}\): Sky cover symbols used in meteorological station models.

Sky cover scale in Oktas	Symbols	Name	Abbreviation	Sky cover fraction (tenths)
0		Sky clear	SKC	0
1		Few clouds	FEW	1
2				2 to 3
3		Scattered clouds	SCT	4
4				5
5		Broken clouds	BKN	6
6				7 to 8
7				9
8		Overcast	OVC	10
(9)		Sky obscured		unknown

Finally, in Figure \(\PageIndex{1}\), notice that the two temperatures on the left side are separated by a series of dots representing precipitation. An excellent guide to precipitation symbols can be found in Figure \(\PageIndex{2}\) and Table \(\PageIndex{4}\).

Figure \(\PageIndex{2}\): The NOAA convention showing precipitation type and intensity on a station model. (Public Domain; Station Model via NOAA/NWS)

Table \(\PageIndex{4}\): Precipitation symbols on a station model and their meaning.

Symbols	Meaning
One, two, or three solid dots in a column	Rain (light, moderate, heavy)
One, two, or three asterisks in a column	Snow (light, moderate, heavy)
A lightning bolt with a dot or asterisk	Thunderstorm (with rain, snow, or no precipitation)
An inverted triangle with a dot or asterisk	Shower (rain or snow)
Two short apostrophe-like marks	Drizzle
Curved lines resembling the number 2	Freezing rain or freezing drizzle
Triangle with a dot	Ice pellets or sleet
Two or three stacked horizontal bars	Fog (thin or thick)
Infinity symbol	Haze