FIGURE 6.4 Photograph taken on March 29, 2004, from the site of the Sulphur Mountain NEXRAD looking approximately west-southwest over the Pacific Ocean and toward the Channel Islands. SOURCE: Julie Demuth, National Research Council.

months, sometimes from thunderstorms or tropical weather systems. Haynes (2001) studied storms that produced at least 3 inches of rain at three or more stations in Southern California and found that most occurred from November through March (Figure 6.5). Table 6.6 illustrates the same information for events of 4 inches or more.

Highest measured precipitation events in Southern California include more than 24 inches in 24 hours (at Haynes Canyon) in mountainous regions. Even with precipitation measured by many rain gauges, actual precipitation measurements still are available for only a small fraction of the overall area of Southern California; thus, it is possible that the largest pre-

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