Observed meteorological data for use in air quality modeling consist of physical parameters that are measured directly by instrumentation, and include temperature, dew point, wind direction, wind speed, cloud cover, cloud layer(s), ceiling height, visibility, current weather, and precipitation amount. These data are used in air quality models to capture the atmospheric conditions occurring at a source and/or receptor location, and therefore, play an important role as they effect the concentration of pollutants at receptors of interest. This site describes and provides the following programs and databases, as commonly utilized by the EPA in conducting air quality modeling:

Surface and Upper Air Databases - Surface data are meteorological data that are measured at the earth’s surface and include physical parameters that are measured directly by instrumentation, such as temperature, dew point, wind direction, wind speed, cloud cover, cloud layer(s), ceiling height, visibility, current weather, and precipitation amount. Upper air data are meteorological data that are measured in the vertical layers of the atmosphere. Much of this data is reported by the National Weather Service (NWS) 

EPA has compiled a database of observed meteorological data over the continental U.S. These data are used in adjusting air quality trends to account for year-to-year meteorological variability. A summary of the contents of the "MetDat" database is contained within the report Details on the Omnibus Meteorological Database (pdf) (7 pp, 288 KB, 01-09-2007).

Meteorological Processors and Accessory Programs - The meteorological processors are used to calculate important meteorological inputs for use in dispersion modeling. The accessory programs are applied to produce graphical or statistical outputs that can aid in the interpretation and understanding of the NWS data or dispersion modeling results.