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<br />(j[jO'Ct94 <br /> <br />H ENZ KELLY & ASSOCIATES <br />Weather Forecasting and Consulting <br /> <br />E. Alternatives: Measured/Computer and Prediction <br /> <br />Two alternatives currently exist to deal with the flash flood problem: one <br />based on event prediction and monitoring and the other based on event measure- <br />ment and computation. Both must deal with the following: <br /> <br />-High degree of "flashiness" of flooding in Front Range Canyon and alluvial <br />fans. <br />-Time needed to make decisions and take actions <br />-High degree of success <br /> <br />. <br /> <br />*Event prediction <br />-Forecast the degree of event severity and potential <br />-Relate forecast to decision matrix and alert officials <br />-Communicate to users <br />-Metwatch situation and storms as potential unfolds <br />-Continually re-assess the potential and implications <br />-Update forecast severity and likelihood <br />-Make evacuation decision before heavy rains start <br />-Communicate . <br />-PLANNED ACTION.....NOT RE-ACTION <br />-When it matters...before the fact. <br /> <br />*Measured-computed <br />-Measure rainfall and/or resulting runoff <br />-Alarm sounds <br />-Basin model projections of runoff <br />-Evacuation decision based on observation projection <br />-React to developing situation <br />-Communicate decision <br />-Warn floodplain and evacuate <br /> <br />It is our contention that a solely measured/computed based flash flood <br />warning system will fail in Colorado and most of the western and High Plains <br />states due to the extreme flashiness of the event meteor10gical1y and hydrologically. <br />The prediction based technique incorporates the measured/computed techniques into <br />its decision matrix but is more reliant on these networks to call off the <br />evacuation of a floodplain. The evacuation decision must be made as reliably <br />and as soon as possible to insure the safety of the inhabitants. It must be made before <br />the event begins the flashflooding process. <br /> <br />1776 South Jackson Street. Denver, Colorado 80210 . (303) 759-1947 <br />