The current conditions are a crucial part to every forecast. Temperature, sky cover, wind direction, etc. are reported by trained weather spotters, the public, and automated systems (typically located at an airport). In fact, our graphics system takes in automated readings from local airports across New York, Pennsylvania, and Canada and generates many of our graphics using them.
Automated Surface Observing Systems, or ASOS, are the most common automated weather systems. Across the United States there are around 1000 federally funded systems that observe temperature, dew point temperature, humidity, air pressure, wind speed and direction, cloud cover, cloud height, horizontal and vertical visibility, weather, and accumulated precipitation. Generally updated once an hour, the systems can take up to twelve reports per hour depending on the severity of the weather.
ASOS only reports what is directly overhead. So, unlike Doppler Radar, is doesn’t detect approaching storms. It also can’t measure snowfall depth. Therefore, a person (typically National Weather Service employee) must take this measurement and adjust any other bad data. ASOS is helpful in determining if precipitation indicated on Doppler Radar is actually hitting the ground or not (known as Virga). It also helps provide a general idea of the weather over a rather large area.
Radiosondes, buoys, and satellites also take information about what is currently happening in the atmosphere; at the surface and aloft. All of this information is important because current conditions are combined with various algorithms to predict what will happen in the future. So good information in gets you good information out. Bad information in gets bad information out and a forecast that isn’t as reliable.
Click here to see New York’s ASOS network.