Laserfiche WebLink
<br />2.3 Radar and related storm observations <br /> <br />Other new data bases and observations of Colorado heavy rain producinn <br />storms were considered, Henz (1974) completed a radar climatology of eastern <br />Colorado thunderstorms using the 10 cm NWS WSI~-57 radar located at Limon, <br />Colorado. His survey focused on severe weather thunderstorms but he included <br />the first compilation of the radar characteristics of Colorado mountain <br />thunderstorm systems, His survey documented 4613 thunderstorm systems and <br />included 71 severe thunderstorms wl1ich remained over the Rockies for their <br />entire life cycle. The key characteristics of these severe mountain thunderstorms <br />were a mean storm radar cloud top height of 44,000 feet msl, an area of greater <br />than 30 dBZ radar reflectivity of 145 square nautical miles, and an area of <br />greater than 40 dBZ of 16 square nautical miles, The average area covered by <br />reflectivities >30 dBZ was about 18 nautical miles ICing by 8 nautical miles wide <br />while the average area covered by reflectivities >40 dBZ was about 5 nautical <br />miles by 3.2 nautical miles, The long axis of the storms aligned with the mean <br />motion vector of the cloud layer winds. These initial characteristics indicated that <br />the mountain thunderstorms were smaller and less intense than their plains <br />counterparts, <br /> <br />A study of high altitude thunderstorm rainfall which occurred above 7,500 feet in <br />Jefferson, Clear Creek, Boulder and Teller Counties during 1979 to 19813 was <br />reported in Henz and Kelly (1989), This survey was updated by Henz (1993) to <br />include the period 1959 to 1991 for the entire Colorado mountains above 7,500 <br />feet. This study indicated 67 events of heavy rainfall equaling or exceeding 1 <br />inch in 30 minutes or less. He concluded that thuncerstorms capable of <br />producing 2 inches of rain in 3 hours or less over areas of 25 square miles or <br />less posed a flash flooding threat to Colorado's mobile recreation population in <br />the mountains. Additionally, several cases of thunderstorms producing 2 to 4,5 <br />inches in 3 hours or less at altitudes betwl~en 7,500 feet and 13,000 feet along <br />the Continental Divide were discussed and identified as posing a flash flooding <br />threat to small alpine water sheds above '10,000 feet. The observed storms were <br />generally of short duration lasting lesS than 4 Ilours. <br /> <br />Stanton (1990) studied in detail the rainfall production of the Big Thompson <br />Canyon storm relative to terrain elevation, He reported that over ,'0 per cent of <br />the rainfall in the Big Thompson stonn fell at elevations between 7,500 feet and <br />9,500 feet. The rainfall which fell at ele1/altions above 10,500 filet accounted <br />for but 0.5 percent of the storm total volumetric rainfall of the Big <br />Thompson Canyon event. This valuable insight into the high altitude <br />rainfall production of an exceptional stt:>rm, regarded by many as having a <br />10,000 year plus return frequency, helps in understanding the potential <br />upper limits for rainfall during extreme precipitation events. <br /> <br />18 <br />