How to Read a METAR Report, Page 2 of 10

Weather observations usually contain the following elements, which I have listed here in alphabetical order:

Maximum and minimum temperatures. Again, how can you forecast what will happen tomorrow if you don't know what happened today?
Precipitation. Usually you want to know not just whether it's raining, but how much it's raining. We will be forecasting precipitation amounts, not just precipitation probabilities.
Present Weather. Usually, whether it's raining or not is of profound importance. Since METAR reports are directed toward pilots, "weather" in a METAR report amounts to anything which reduces the visibility, including not just things like rain or snow, but less exciting events like fog or blowing dust. The definition is bent a little to include things like funnel clouds, which only affect the visibility in certain directions.
Pressure. Not as important as you might think, but useful for diagnosing frontal passages, etc.
Station and Time. Fundamental, but often overlooked.
Temperature. Of obvious importance. This is what we'll be forecasting.
Wind. In a few hours, air can travel over a hundred miles. You need to look upstream to find out what temperatures will be like downstream. And a wind off the water can feel a lot different from wind coming off the mountains.

There are about fifty other types of weather elements, and most of them are essential to weather forecasting at one time or another. I'll be describing them as we encounter them in specific examples.

Which one of these elements would you say is most important for making a weather forecast?

As a general rule, the raw, undecoded reports are more reliable. As a report gets decoded by computer, information gets lost or misinterpreted. With a perfect decoder (and perfectly coded observations), this might not be a problem, but unfortunately, most decoders are far from perfect. So, I'll start by showing you how to access and read the decoded reports, and then progress to the raw reports, the ones that REAL meteorologists read.

Questions or Comments

Technical: E-mail John Fulton < jdfult@nimbus.met.tamu.edu >
Scientific: E-mail Dr. John Nielsen-Gammon. < nielsen@ariel.met.tamu.edu >