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~ Q I I I I I I I I I I I I I I I I I If you insert the values for PWI and the depth of the warm layer into equations (2) and (3), the peak 60-minute rainfall rate is 3.42" and the peak 30- minute rainfall rate is 2.38 inches. These rainfall rates are assigned to the grid squares covered by radar reflectivity values of 50 dBZ or greater. Lower rainfall rates are assigned to lower reflectivity values as shown in Table 2. Radar dBZ " Level Peak 60-min Peak 30-min 25 30 0.72" 0.50 35 1.20" 0.85 40 1.92" 1.34 45 2.40" 1.68 50 3.36" 2.38" 55 3.36" 2.38" Table 2 Relationship Between Peak 60-Minute and Peak 30-Minute Rainfall Rates and Radar Reflectivity Levels. HMS utilized the Doppler radar from the National Weather Service (NWS) WSR-88D located at Pueblo, Colorado. This radar is located about N115 miles from the basin and provides fairly accurate radar reflectivity observations. HMS notes that the Pueblo is slightly affected by the passage of its beam over higher terrain to the west. HMS estimates that up to 30% of the lower half of the beam may be attenuated as it shoots towards the Saguache location along a 255- degree radial. However, this factor matters little as HMS does not use the absolute strength of the radar reflectivity to calculate the rainfall rates but rather uses the strength of the maximum reflectivity to identify the location of the heaviest rainfall. The rate is calculated by the HMS 2-D cloud model. As the radar reflectivity data field is received and mapped; each grid square is assigned a reflectivity value of 0 through 7. Table 2 above shows the reflectivity values and their associated dBZ values. 3.4 Analysis of Radar Reflectivity and Rainfall This section will encompass an examination of the radar reflectivity pattern and the rainfall pattern that accompanies it. The resolution of the radar reflectivity data allows it to define the radar reflectivity for 0.65 by 0.65 square mile area. Figure 6 shows a summation of the reflectivity value for each grid square for the duration of the storm. Note that a rainfall rate (See Table 3) is assigned to each radar reflectivity factor for each observation and the storm total rainfall is a summation of these individual rainfall observations. Note that the grid is segmented into an outer and inner grid and that the inner grid is split along the stream location of the valley of the basin. 10 .-