Making Observations of the Atmosphere

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


By the time you are finished reading this page, make sure that you understand when standard hourly observations are collected and for what hour a particular observation qualifies based on its time stamp. 


Forecasters worth their salt routinely use current weather and recent history as the basis for predicting the future. That's because current and past weather can, and often does, offer clues about how the atmosphere will evolve. During winter and early spring, for example, powerful Pacific storm systems that make news on the West Coast by spawning heavy coastal rains and mountain snows often make news a few days later when they arrive over the Middle West, generating fierce thunderstorms that can spawn tornadoes.

However, even in more benign weather patterns, conscientious forecasters routinely study weather conditions "upstream" of their location (by upstream, I mean where weather systems are coming from), hoping to extrapolate these conditions into the future to get a more accurate beat on the local weather forecast. There's a big payoff to forecasters who are sticklers for such details. Indeed, the wealth of surface observations taken hourly across the nation often tips the atmosphere's hand and gives meteorologists a leg up on important clues to the weather forecast.

At all U.S. airports, standard hourly weather observations are taken once each hour, typically several minutes before the top of the hour. So, for example, the standard 3:00 PM observation might have a time stamp such as 2:53 PM. More formally, standard hourly weather observations are issued between 50 minutes past the hour and the top of the next hour, so a standard 3:00 PM observation could be time stamped between 2:50 PM and 3:00 PM. When weather conditions rapidly change, however, you'll often see special observations, known as SPECI reports, at other times. A "special ob" taken at 3:15 PM, for example, falls under the umbrella of the 3:00 PM observation, even though the standard observation was taken a little before 3:00 PM. In general, all observations time-stamped between (hh-1):50 to hh:49 are part of the hh observation cycle (hh represents any given hour). So, continuing with our example, any observation time-stamped between 2:50 PM and 3:49 PM belongs to the 3 PM observation cycle. The 4:00 PM observation cycle begins at 3:50 PM, and so on.

A collection of weather instruments alongside of a runway
An automated observing system at the airport in Elko, Nevada. Many airports in the United States use the Automated Surface Observing System (ASOS). Read more about ASOS.

As you might expect, there's an avalanche of surface weather observations each hour from all the airports across the country (and across the world, for that matter). In order to simplify life and create easy-to-read weather maps, the National Weather Service organizes hourly observations onto templates called station models. In the remainder of this lesson, you'll learn how to decode surface station models (and thus determine local weather conditions). However, before we tackle the rules and conventions for decoding station models, you'll need to know how weather observers all over the world synchronize their watches in order to standardize the times that weather observations are taken.

Quiz Yourself...

Try your hand at the questions below to make sure you have a handle on observation times.

Explore Further...

If you want to look ahead, here's the most recent surface map of station models for the contiguous states. Please note that the map was purposely designed to include a limited number of station models (a map with all the station models would be very cluttered). We'll work on decoding station models later in the lesson, but If you want to skip ahead and try decoding a few on your own, check out this explanation on decoding station models from the Weather Prediction Center.