National Weather Service

In 1994, the National Weather Service began to operate a Next Generation Weather Radar on Sulphur Mountain in Ventura County, California. A recent study by the Rose Institute of Claremont McKenna College concluded that the radar's location prevented it from providing accurate and timely information to be used for warnings about flash floods and wind shear. This report determines whether the Sulphur Mountain Next Generation Weather Radar (1) can provide timely and accurate information for warnings about flash floods in nearby communities 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.

Recommendations

Our recommendations from this work are listed below with a Contact for more information. Status will change from "In process" to "Open," "Closed - implemented," or "Closed - not implemented" based on our follow up work.

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