A weather station model is a standardized, compact display of meteorological observations for a specific location. Meteorologists created this symbolic shorthand to convey complex weather data in a small space on a synoptic weather map. This plotting system allows analysts to quickly view and compare conditions like temperature, pressure, wind, and sky cover across a wide geographic area at a single moment in time. By learning to decode the numbers and symbols, anyone can gain insight into the current state of the atmosphere at the station’s location.
Understanding the Standard Layout
The structure of the station model is designed for efficiency, with each observation occupying a fixed position relative to the central station circle. The shading of this central circle indicates the fraction of the sky covered by clouds. The air temperature is conventionally located in the upper-left position. Directly below the temperature, in the lower-left area, is the dew point temperature, which indicates the moisture content of the air.
On the upper-right side, the atmospheric pressure is plotted, with the pressure tendency—the change over the last three hours—positioned below it. Current weather phenomena, such as rain or fog, are represented by a symbol placed to the left of the central circle. Extending from the central circle is the wind barb, which graphically depicts both the wind’s direction and speed.
Decoding Numerical Data: Temperature and Pressure
Temperature and dew point readings are located on the left side of the model. The upper-left number is the air temperature, and the one directly below it is the dew point temperature. Both are often given in degrees Fahrenheit or Celsius. These values represent the current thermal conditions and moisture saturation level of the air. A small difference between these two numbers signifies high humidity, as the air temperature is close to the condensation point.
Atmospheric pressure, plotted in the upper-right, requires a specific conversion because it is abbreviated to save space. The model displays only the last three digits of the sea-level pressure, measured in tenths of millibars (or hectopascals). To reconstruct the full pressure value, a decimal point must be placed before the final digit. For example, a plotted reading of “997” becomes 99.7, and “028” becomes 02.8.
The next step is to determine the missing leading digits, typically a ‘9’ or a ’10’. Choose the leading digit that results in a value closest to the standard atmospheric pressure of 1000 millibars. If the three-digit number is less than 500, a ’10’ is usually placed in front (e.g., “028” becomes 1002.8 mb). Conversely, if the three-digit number is 500 or greater, a ‘9’ is typically prefixed (e.g., “997” decodes to 999.7 mb).
Below the abbreviated pressure is a two-digit number and a symbol indicating the pressure tendency. The number represents the net change in pressure over the past three hours, measured in tenths of millibars. A value of “12” means the pressure changed by 1.2 mb. An accompanying symbol, such as a line slanting up and to the right, indicates a steady rise. Rising pressure often suggests improving weather, while falling pressure can precede the arrival of a storm system.
Interpreting Symbolic Data: Wind and Sky Conditions
Wind data is conveyed through the wind barb, a line extending from the central circle. The direction of this line indicates the direction from which the wind is blowing. For example, a barb pointing toward the northeast signifies a southwest wind. Wind speed is determined by the combination of short lines, long lines, and pennants attached to the barb’s end, with speeds measured in knots.
Calculating Wind Speed
Each long line, or full barb, represents 10 knots, while a short line, or half barb, adds 5 knots to the total speed. A solid triangular flag, known as a pennant, signifies 50 knots. To calculate the wind speed, the values of all attached barbs and pennants are simply added together. For instance, one pennant, one long barb, and one short barb would total 65 knots.
Sky Conditions
Sky conditions are illustrated by the shading within the central station circle, which represents the total cloud cover in eighths, known as oktas. An empty circle denotes a clear sky, while a completely filled circle signifies overcast conditions. Various levels of partial shading correspond to different cloud fractions like scattered or partly cloudy skies.
Current Weather
The current weather symbol is located to the left of the central circle and uses a specific icon to represent present conditions. These symbols depict phenomena such as rain, snow, fog, or thunderstorms. For example, three dots could represent moderate rain, while an asterisk symbol would indicate snow. This visual element gives an immediate summary of the precipitation or visibility conditions occurring at the station.
Applying the Knowledge: A Step-by-Step Read
Reading a complete weather station model involves systematically translating each element using the established layout and conversion rules. Begin with the numbers on the left: the air temperature in the upper position and the dew point below it. Next, observe the central circle’s shading to determine the cloud cover. If a symbol is present next to the circle, identify the current weather condition it represents.
The wind barb is then interpreted to determine the wind’s direction and speed in knots. Finally, decode the atmospheric pressure in the upper-right corner by adding a decimal point and prefixing a ‘9’ or ’10’ to find the full millibar value. Below the pressure, interpret the two-digit number and accompanying symbol to understand the pressure trend.