National Weather Service:

Sulphur Mountain Radar Performance

AIMD-99-7: Published: Oct 16, 1998. Publicly Released: Oct 16, 1998.

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Pursuant to a legislative requirement, GAO reviewed the Rose Institute of Claremont McKenna College's study on the National Weather Service's (NWS) Next Generation Weather Radar (NEXRAD) located on Sulphur Mountain, California, focusing on whether the Sulphur Mountain NEXRAD: (1) can provide timely and accurate information for warning of flash floods; and (2) is intended to provide low-level data necessary to predict wind shear for Los Angeles International Airport.

GAO noted that: (1) since the Sulphur Mountain NEXRAD was commissioned in December 1994, the accuracy and timeliness of flash flood warnings has improved for Ventura and Los Angeles counties; (2) from January 1992 through December 1994, 18 flash flood events were reported in Ventura and Los Angeles counties; (3) however, from January 1995 through February 1998, advanced warnings were issued for 17 of the 22 reported events; (3) although the Sulphur Mountain radar is not the only source of data on which flash flood warnings are issued, NWS officials believe that the Sulphur Mountain NEXRAD is the primary reason for the increase in advanced warning lead time because it provides advanced warning of heavy precipitation, often before severe weather hits the California coast; (4) users of the Sulphur Mountain NEXRAD data told GAO that the information it provides is valuable, accurate, and timely; (5) despite the improvements in flash flood warning lead time and user satisfaction, NWS data show that the Sulphur Mountain NEXRAD is not consistently meeting its 96-percent availability requirement; (6) from October 1995 through March 1998, the Sulphur Mountain NEXRAD was available as required for 20 months; for the other 10 months, availability ranged between 79 to 95 percent; (7) if the NEXRAD is not available as required, it increases the risk that NWS will not have the data it needs to accurately and quickly predict flash floods and other severe weather; (8) NWS headquarters officials acknowledged the availability shortfalls and stated that they are monitoring the failure rates of parts and are attempting to reduce the failure rates or to more quickly replace the parts that fail most often; (9) predicting wind shear at Los Angeles International Airport is not part of NEXRAD's mission; (10) the Federal Aviation Administration (FAA) uses three different systems to predict wind shear at airports--Terminal Doppler Weather Radar (TDWR), Weather Systems Processor (WSP), and Low Level Wind Shear Alert System (LLWAS); (11) TDWR is being deployed at high traffic airports that experience severe weather; (12) WSP is an enhancement to an existing air traffic control surveillance radar that is to provide FAA with 80 to 95 percent of the capability of TDWR; (13) WSP is to be installed at high to moderate traffic airports that experience limited severe weather; (14) LLWAS is used to supplement TDWR at nine high traffic airports at greatest risk of severe weather and it is used at other airports that will not get TDWR or WSP; and (15) Los Angeles International Airport currently has LLWAS and is scheduled to get WSP in 2001.

Recommendation for Executive Action

  1. Status: Closed - Implemented

    Comments: NWS agreed with the recommendation and implemented several key changes at the Sulphur Mountain site that improved the radar availability above the 96-percent minimum requirement. For example, specific high failure components were identified and replaced, producing a much more stable environment; a new plan was implemented to expedite delivery of spare parts; a revised notification and reporting policy for electronics technicians was implemented to reduce trouble response time, and a remote terminal was installed to diagnose and restart the system. As a result of these changes, radar availability exceeded 98 percent from June 1998 through May 1999, according to data from NWS's Office of Systems Operations.

    Recommendation: Since the Sulphur Mountain NEXRAD is not always available as required, the Secretary of Commerce should direct the National Oceanic and Atmospheric Administration Assistant Administrator for Weather Services to determine all the reasons why the Sulphur Mountain NEXRAD is not meeting the 96-percent availability requirement and to correct the problems so that the radar is available as required.

    Agency Affected: Department of Commerce


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