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127 <br /> Also of importance is the sequence of the four 15-min incremental PMP <br /> values. We recommend a time distribution, table 4.8, giving the greatest <br /> intensity in the first 15-min interval (U.S. Weather Bureau 1947). This <br /> is based on data from a broad geographical region. Additional support for <br /> this time distribution is found in the reports of specific storm by Keppell <br /> (1963) and Osborn and Renard (1969). <br /> Table 4.8.—Time sequence for 15-min incremental PMP within 1 hr. <br /> Increment Sequence Position <br /> Largest 15-min amount First <br /> 2nd largest Second <br /> 3rd largest Third <br /> least Last <br /> 4.8 Seasonal Distribution <br /> The time of the year when local-storm PMP is most likely is of interest. <br /> Guidance was obtained from analysis of the distribution of maximum 1-hr <br /> thunderstorm events through the warm season at the recording stations in <br /> Utah, Arizona, and in southern California (south of 37°N and east of the <br /> Sierra Nevada ridgeline). The period of record used was for 1940-72 with an <br /> average record length for the stations considered of 27 years. The month <br /> with the one greatest thunderstorm rainfall for the period of record at each <br /> station was noted. The totals of these events for each month, by States, <br /> are shown in cable 4.9. <br /> Table 4.9.--Seasonal distribution of thunderstorm rainfalls. <br /> (The maximum event at each of 108 stations, period of record 1940-72.) <br /> 1 <br /> Month <br /> M J J A S 0 No. of Cases <br /> Utah 1 5 9 14 5 34 <br /> Arizona 4 16 19 4 43 <br /> S. Calif.* 14 10 7 31 <br /> • <br /> No. of cases/mo. 1 23 35 40 9 0 <br /> *South of 37°N and east of Sierra Nevada ridgeline. <br /> 1 <br />