Lesson 1. An Introduction to Atmospheric Variables

This is a sample lesson page from the Certificate of Achievement in Weather Forecasting offered by the Penn State Department of Meteorology. Any questions about this program can be directed to: Steve Seman


Young child standing next to an instrument shelter
A cooperative weather station at Granger, Utah (circa 1930).
Credit: NOAA Photo Library

Like many scientists, meteorologists rely on an army of technical assistants to take observations in their "open-air laboratory" (a.k.a. the atmosphere). Approximately 11,000 "cooperative observers" volunteer to observe daily precipitation and maximum and minimum temperatures in their hometowns. These ordinary citizens (many of whom are weather enthusiasts) provide crucial data that supplement the National Weather Service's primary network of observations (taken at approximately 1500 airports across the nation).

At these "primary" airports, however, trained government observers or automated weather instruments are responsible for collecting routine weather observations. The set of routinely collected measurements includes temperature, moisture, air pressure, wind direction, wind speed, cloud cover, visibility, precipitation and several other atmospheric variables.

This lesson will immerse you in the culture of weather observation. You will learn about some of the key weather variables and why forecasters are interested in these parameters. You will also learn about how all of these observations can be easily displayed on weather maps. This knowledge allows you to take the first step toward your goal of becoming a competent apprentice forecaster. By gaining insight on the atmosphere's present state, you will be better prepared to fashion your own weather forecast, or at the very least, give more context to the weather forecasts you see and hear on television and radio.

Lesson Objectives

After completing this lesson, you should be able to:

  • Explain when the standard hourly observations are collected and for what hour a particular observation qualifies based on its time stamp. (2)
  • Convert times displayed on weather maps in GMT to a station's local time (and conversely, be able to convert a station's local time to GMT/UTC using appropriate nomenclature).(1)
  • Identify the temperature variable (with proper units) from a station model and convert to the observation to other units.(1)
  • Identify, decode, and interpret the visibility observation on a station model (if displayed).(1)
  • Explain when an "obstruction to visibility" symbol (that is, present weather) must be listed along on a station model, and identify and decode the "present weather" symbol  (if shown).(1)
  • Identify and explain the dew point temperature variable (with proper units) from a station model.(1)
  • Interpret a station model's sky coverage symbol, giving the official cloud coverage classification and fractional equivalent.(1)
  • Identify and decode the sea-level pressure variable from a station model.(1)
  • Express the wind direction and speed (including the units) for a given station model "flag."(1)

(Numbers denote mapping to course objectives)