The site is extensive. As Mr. Hoffman found, the deeper into the site you go, the more technical the information becomes. To prepare forecasts, the National Weather Service and the Federal Aviation Administration collect data from weather stations at most airports and other sites once every hour. Doppler radar detects the location and intensity of rain, snow and other forms of precipitation. Meteorologists at the National Weather Service and some independent weather companies, like AccuWeather and the Weather Channel, run the weather service information through computer models that generate forecasts.
Meteorologists then interpret the data.
The information is packaged and sent to media organizations and is also put on Web sites. Local meteorologists often gather additional information to compile forecasts. The data is culled from instruments, including Doppler radar owned by the broadcast stations, and from local weather stations, including one or more of roughly 4,000 schools set up with instruments through a program sponsored by AWS through its School WeatherNet program. Despite the vast amount of information, weather forecasting is still inexact. One model might indicate rain in the morning, Ms. Church said, while another might predict rain later in the day.