On Tuesday November 18, 1997, at 1500 Universal Time Coordinated (UTC), the NWS Office of Systems Operations (OSO) will begin implementing phase one of the Communications Identifier Changes. In phase I, guidance and public forecast WMO headers will change as part of the transition to the Advanced Weather Interactive Processing System (AWIPS) era. A list of the affected products and their headers is available on the OSO Systems Operations Change Notices web page at : http://www.nws.noaa.gov/oso/notices/notices.shtml. (Click on CID 97-3 Phase I Communications ID Implementation Plan Heading Changes list.)
During a review of ground station reporting records, the WMO Working Group on Observations found that the transition away from omega sondes was proceeding well. 176 of the 241 radiosonde worldwide sites using omega frequencies were planning to use alternate systems (GPS being the most popular alternative), 46 sites had no definite plans, and 19 sites were not heard from. Overall in September , 656 upper air stations were making radiosonde observations worldwide at 00 and 12 UTC. This represents approximately 75% of the raobs requested for the global observing system. After the omega frequency denial in October 1997, approximately 50 stations stopped reporting.
Deletion of the visible check in the cloud detection algorithm has alleviated a problem with spurious clouds in mountainous terrain. Spurious clouds have recently been detected around the 19-23 UTC time window in the mountainous and rough terrain regions of Colorado, Wyoming, New Mexico, Arizona, Nevada, and California. The cause is probably a relatively high surface albedo observed by the GOES 9 visible sounder. These are probably due to a thin layer of snow and/or lack of vegetation at this time of year. The incorrectly defined cloudy regions prevented useful temperature/moisture retrieval and created a false relative maximum of low level cloud top pressures.
