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<br />H ENZ METEOROLOGICAL SERVICES <br />Ml~teorological Consulting and Weather Forecasting <br /> <br />January 3, 1991 <br /> <br />Mr.Larry Lang <br />Colorado Water Conservation Board <br />Sherman st. <br />Denver, CO <br /> <br />Dear Mr. Lang: <br /> <br />HMS has completed a preliminary re-constitution of a heavy rainfall <br />event affecting the Frenchman creek basin from 11:00 PM, July 29, 1989 <br />to 5:00 PM, July 30, 1989. The preliminary re-constitution of rainfall <br />relied on a synthesis of officiil.l radar echo 16mm film observations from <br />the NWS WSR-57 radar at Limon, colorado, upper air observations from NWS <br />Forecast Office in Denver, Colol'ado, and surface observations taken by <br />FAA observer at Akron, Colorado, The NWS surface an'd upper air <br />observations were used to initialize the HMS Convective Storm Model <br />(CSM). The CSM model produced the storm mass curve, radar-rainfall rate <br />relationship and the estimated Frenchman Creek basin rainfalls. <br /> <br />The CSM radar-rainfall relationship was compared to observed rainfall <br />at Akron NWS Co-operative site for goodness of fit. The CSM estimated <br />rainfall of 0.95" compared to observed 1.10" or 86% of the observed. <br />Thus our estimated rainfalls are considered to be conservative by about <br />15%. <br /> <br />We are forwarding a copy of the cumulative rainfall for the Frenchman <br />Creek 8asin for the West, Central, and Eastern thirds of the basin. <br />Time is given in local Mountain Daylight Time and Storm Cumulative Time, <br />Figure 1 shows a plot of cumulative rainfall versus cumulative time. <br /> <br />Our radar analysis confirms that the Frenchman Creek flash flooding <br />was not caused by any portion of the Greeley Flood storm. Rather it was <br />composed of two primary thunderstorms crossing portons of the basin <br />between 11:00 PM, July 29, 1989 and 4:00 PM, July 30, 1989. storm 1 <br />dropped about 2.30 inches of rain on the western third of the basin near <br />midnight. This storm moved south to north and focused on an area north <br />and west of Sterling. The second storm moved forward, west of the basin <br />about 11:00 AM on the 30th and crossed most of the basin from southwest <br />to northeast. Figure 2 is an estimated "storm total" rainfall for the <br />bas in from 11: 00 PM on the 29th to 4: 00 pr1 on the 30th. <br /> <br />Our billing will follow with a net 15 days payment request. I will be <br />glad to answer any further questions or provide more detailed <br />information. <br /> <br /> <br />- ~ <br />2480 West 26th Ave., Bldg. B, Denver. Colorado 80211 . (303) 458,1464 <br /> <br />Exhibit 1-1 <br />