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LAND STATION DEFINITONSGo to Dataset: The terms "first order" and "second order" have not been evenly applied over the years by different agencies.
First Order generally means a 24-hour per day, year-round observing schedule with trained, certified observers. There are about 270 NWS First Order Stations, most converting to ASOS. The military also operates a few hundred hourly stations in the U.S. and overseas.
Second Order generally means hourly airways observations are taken, but not in accordance with first order requirements as stated above. Of about 1000 stations, most are FAA-operated, and 170 are run by the Coast Guard. Many second order stations and staff are supervised and trained by NWS. Many are also automated via various AWOS configurations.
ASOS has confused the issue somewhat, as there are various levels of augmentation available for ASOS. Of the hundreds of ASOSs planned, 32 will be staffed continuity sites with both manual and ASOS obs taken for a few seasons to years.
Airways (not a WMO code) simply refers to the code used for hourly observations at airports, or sometimes city offices. It is the code that gives sky conditions (clear, scattered, broken, overcast); ceiling height; visibility; wind; temperature; dewpoint; etc. It is to be distinguished from the WMO SYNOP 3-hourly or 6-hourly code that is in a different format and used internationally for primary synoptic reporting stations. Airways codes are slated for replacement by a version of the WMO METAR Code in January 1996. Some overseas U.S. stations and most foreign airport stations now use WMO METAR (which is being modified and expanded by WMO).
In all there are about 1300 stations that report some form of hourly airways or coastal observations, full or part time, in the U.S.
Co-op stations are defined as stations operated by the NWS Cooperative Weather Observing Program for climate observations as documented by NWS Form B-44. They take one observation per day including precipitation (water equivalent, snowfall, snow depth) at about 8000 sites, of which about 5500 also observe max and min temperature and temperature at observation time. A few report soil temperature and/or evaporation. Many hourly reporting stations are also Co-op stations. The hydrological Hourly Precipitation Station Network contains about 2500 stations, and operates in basically the same way as the Co-op Network, except the only variable addressed is hourly water-equivalent precipitation. Instrumentation and observing schedules are documented in the NCDC Station History data base. They do vary with time and place. Virtually all NWS 24-hour manual and ASOS stations are or will likely be considered a part of the Co-op Network.
Among NWS, AWS, the US Navy, FAA, other state and federal agencies and foreign countries the variety of station types is large and overlaps are plentiful. The easiest way to classify them is probably:
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A call, E-mail, or fax to NCDC should help clarify the station and data types available in any area/time span of interest.
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| Updated 22 July 2005 |
