availability of the Sulphur Mountain radar exceeded the availability requirements established by the NWS.

The committee performed its own calculations of low-level radar coverage using 30-m digital terrain elevation model data, considering the full extent of the radar beam (i.e., not just the axis, as in some prior studies) and assuming standard atmospheric propagation conditions. An integrated analysis of the coverage provided by the Sulphur Mountain NEXRAD and the adjoining Vandenberg Air Force Base, Santa Ana Mountain, Edwards Air Force Base, and San Diego NEXRADs reveals overlapping coverage for much of the area. However, there is an area southwest of the Sulphur Mountain radar over the Pacific Ocean that is covered exclusively by this radar. Low-level coverage of this area from which storms often approach is important for monitoring incoming storms and assessing their flash flood potential before they move onshore. Although the center of the Sulphur Mountain radar beam at the current minimum antenna elevation angle of 0.5° rises above 1.83-km (6000-ft) altitude beyond 75 km from the radar site, half of the radar beam is below that level at this range and has enabled detection of approaching storms. The committee did a hypothetical analysis with the radar antenna lowered to 0.0° and found that this would provide beam-axis coverage at or below 1.83 km (6000 ft) out to 125 km.

The committee examined the LOX WFO’s flash flood warning statistics and found that it has an excellent record of issuing flash flood warnings. The proportion of flash flood events with advance warning and the average warning lead time more than doubled following the commissioning of NEXRADs nationwide, including the Sulphur Mountain radar. When the LOX statistics are compared with those of the other 115 WFOs throughout the continental United States, their percentage of flash flood events with advance warnings, at 79 percent, is better than the national average of 69 percent. LOX’s ratio of flash flood events that were forecast but failed to materialize (called the false alarm ratio) is less than the national average.

The average lead time for flash flood warnings from LOX is less than the national average. The national statistics, however, are skewed by the large numbers of WFOs that forecast for regions with little to no relief in the surrounding topography. A more accurate assessment of the LOX WFO’s performance is gained by comparing LOX with the 2004 goals of the NWS Western Region, which are established by considering the complex terrain in the western United States and thus the greater tendency for rapid onset of flash flooding. LOX’s average lead time, as well as the percentage of forecast events and the false alarm ratio, is superior to the 2004 Western Region

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