Real-World Computing: Weather

The US National Weather Service makes a huge amount of weather information available for free on the Internet and other media. The ultimate purpose of this effort is to save lives; the sooner people hear about severe weather conditions, the better prepared they will be when it arrives. Even minutes can make a difference.

Current Conditions. The current conditions at most airports around the world are gathered hourly, either automatically or manually, and submitted in METAR format. This format is a compact string that represents location, time, temperature, visibility, cloud cover, atmospheric pressure, precipitation, etc. This information is available via FTP or EMWIN (see below).

There is also personal weather station hardware made by Oregon Scientific and others. These systems would allow real-time collection of current conditions data.

Radar Images. The NEXRAD system collects huge amounts of radar data from 154 sites around the country. This information is compiled into graphics files available via FTP. It is also available live in streaming form, if you connect a T1 network connection directly to the NWS, can receive 35 gigabytes of information per day, and can pay the recurring maintenance fees. Unfortunately, that's not really feasible for most of us.

The EMWIN system broadcasts a very coarse radar image that shows the entire United States precipitation activity.

Watches and Warnings. The EMWIN system broadcasts a stream of information via satellite, radio, and internet. This stream contains warnings, watches, forecasts, current observations, climate data, and even some graphics. It is available at no cost and you are free to do anything you like with the information. Warnings and other time-sensitive information are broadcast immediately over the EMWIN network, and are available within seconds of their publication. Of course, to effectively receive this information, you must be either permanently connected to the internet, have a radio receiver, or have a satellite downlink system.

Forecasts. One of the types of information EMWIN broadcasts is forecast information of various types.

The EMWIN System

As you can see from the above list, the EMWIN system is a great source for all kinds of weather information. Fortunately for internet users, this information is available over the internet for free. All you need is software to receive and decode the information stream.

There are several commercial vendors that sell programs to receive and process the EMWIM data stream. I am also in the process of writing my own software to receive this data.

Greg Hewgill <>