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I I I I I I I I I I I I I I I I I I I is no longer present in the grid. A quick examination of this period shows that some of the strokes do appear to be on the edge of the 30+ dBZ areas however, the orientation of the strikes with respect to the reflectivity pattern does not appear to have a discernable pattern due to the scattered nature of the radar reflectivity at this time. 4.3 CG Data and Grid Averaged Rainfall Rates A comparison of the grid averaged rainfall and CG rates for 5 minute intervals is shown in Figure 10 for the entire analysis grid while Figure 11 shows the same rate for the sub-grid area where the heaviest rain fell. . The grid averaged rainfall rate was simply derived by averaging the derived 5-minute rainfall rates over the grid of the area. A brief glance at these two graphs shows that the timing of the increases, peaks, and decreases in average rainfall vs. CG lightning indicate that the peak rainfall rate precedes the corresponding CG intensity by 5-10 minutes. When the CG and rainfall data is further broken down into a sub-grid area that is roughly defined as > 3.00" storm total rainfall, the lag in the near area CG stroke counts with respect to the sub-grid averaged rainfall rates is increased to about 10-15 minutes (Figure 11). This pattern is suggestive of the existence of a warm coalescence rainfall mechanism operating. Warm coalescence rainfall periods usually produce the heaviest rainfalls and rainfall rates and low lightning rates frequently appear during the periods of heaviest rainfall during flooding events. 5.0 Relationship of Rainfall to Topography A constant source of debate concerning the rainfall limits of heavy rain has existed since the mid-1980s. Table 4 shows the average and range of rainfall rates for the storm versus elevation. Note that the heaviest rainfall fell between 8,000 feet and 9,000 feet in the valley with over 4.00 inches of average rainfall. It is interesting that for every 1,000 feet of elevation increase the base rainfall decreases about 25 percent. If this relationship holds up in other storms, it could have a profound impact on the calculation of elevation adjustments to site specific Probable Maximum Precipitation (PMP) calculations. . Elevation,Barid Above 10 000 feet 9000 - 10 000 feet 8 000 - 9 000 feet ",era e,Rainfilll' 1.85" 3.25" 4.35" Table 4 Relationship of Rainfall Amount to Elevation 17