We start with data -- winds that are measured about 10 m above the surface at locations throughout Northern California. The map shows the locations of sites from which the data that we use are frequently obtained. The National Weather Service (NWS), FAA, Navy, Coast Guard and Air Force all provide input observations, as do several private and local government organizations such as the Bay Area Air Quality Management District (BAAQMD), Lawrence Livermore National Laboratory, utilities and oil companies. Data are not available every hour from every station, but we usually have data from 20 or more sites. Data are also obtained from other sites not shown, e. g. Sacramento, Fresno etc. Winds and temperatures aloft are only available twice daily (about 4 a.m. and 4 p.m.) from a balloon launched by the National Weather Service from the Oakland airport. The most recently measured upper air information is collected for use.