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. "..,.>:;",~ ,-,~.,:.."i,~!.i..~,-,Lu~_' From the CG maps it appears the Opal storm beg;an along a gust front which propagated northward up the plateau surrounding Opal. Initial storm formation began between 1530 LDT and 1600 LDT to the southeast of area where the heaviest rain eventually fell. Between 1600 LDT and 1630 LDT a roughly west to east line of multi... cell thunderstorms formed and became stationary from Nutria to 20 miles east of Nutria. The heavy rainfall center remained east of US 30. The most intense rain period began about 1630 LDT and ended about 1715 LDT. The storm area shrank and rainfall diminished between 1715 LDT and 1745 LDT and by 1800 LDT the Opal stonn had ended. A summary of the CG production and aerial coverage of storm cells for] 5 minute periods is presented in Table 2. The aerial coverage pertains to the estimated area in square miles covered by 5 or 6 level radar echoes or the region of heavy rainfall. The moderate rain area was much larger than this heavy rain area. On the other side ofthe slash ( 1 ) are the number of CG' s produced by the storm cell during the 15 minute time perio(l. From Table 2 it is apparent that the heavy rain area fi'om the thunderstorm complex was typically about 30 to 50 square miles during the heaviest ]5 minute portion of the storm. While the stOlID line was roughly stationary, some movement of the heavy rain areas was noted. The total aerial coverage of the heavy rain area where amounts reached or exceeded 1.5 inches is shown in Figure 23. Two heavy rainfall centers of more than 1.5 inches ofrain appear. One c{~nter is about 9.4 miles by 8.6 miles or 80.6 square miles in area while the other eenter is 6.25 miles by 3 miles or 18.75 square miles nn area. Thus the aerial coverage of the Opal stonn is about 100 square miles with gi'eater than 1.5 inehes of rain and about 50 square miles with greater than 5 inches of rain. The size of the Opal storm is larger than most local storms. _ The early assumption rnad.e by Table 2. Aerial coverage(sq. mi) and 15 minute CG production by the Opal Storm Cells between 415 PM (LDT) and 600 PM (LIlT) :, Time ; W .Celli...... ..... ,CeIlT' . " 415-430PM, 12.5/14 2.515 . 430-445PM 9.2/12 11.2114 ..445-500PM 11.4/18 9/25 ISOO-515PM 15/16 -- -- ['515-530P.M:. S30-545PM ;.c545c600PM 1;<1.' '. . ... -..,' ',' Sq. mi/CG sq. mi/CG - Cell 3 11/12 14/13 ]0/23 26.4/42 31.3161 ---- 21.3/15 19.4/14 Cell 4 . 9.9/12 12.5/32 19.8/28 8um 35.9/43 46.7/71 50.2/94 41.5/58 ',1.3/61 21.3115 19.4/14 -- ~L!:~i/CG s,s; mi/CG ~. mi/CG Note: Each column shows the area of the storm cell and the number of CG's produced during the 15 minute observation period. 41