FLOOD09830 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I II I I I I I I I I I The stonn then proceeded to move almost due south with little change in intensity until it moved into Gilpin County about 19451. Visual observations of the stonn complex noted very active cloud-to-ground lightning as the stonn crossed into Boulder County and began to move east of the Continental Divide. An operational meteorologist participating in the Urban Drainage & Flood Control District's (UDFCD) Flash Flood Prediction Program (F2P2) at HMS made note of the very vigorous appearance of this stonn and its lightning production in the F2P2 log at 19001. Despite the stonn's active appearance no reports of heavy rain, hail or lightning damage were noted from Boulder County. Rapid intensification of the stonn began shortly after it crossed into Gilpin County about 1953L and continued until about 2140L as the stonn moved across eastern Clear Creek County and into western Jefferson County. The peak radar intensity of the stonn was reached between 2030L and 2130L as it crossed Virginia Canyon, Interstate 70 and extreme northeastern Clear Creek County. Nearly continuous lightning was observed to the west over the foothills from the Denver metropolitan area by numerous weather observers. Locally heavy rainfall was produced by the stonn from about 20 15L until about 21151. The rain produced flash flooding in portions of Gilpin and Clear Creek Counties in the immediate vicinity ofIdaho Springs and Central City. Newspaper and stonn reports obtained by the NWS are presented in Figures 4 and 5 which describe the flooding problems. The stonn began to slowly dissipate after 2145L though it continued to produce a spectacular lightning display as it moved southward across the western Jefferson County foothills. No further reports of flash flooding were received once the stonn moved into Jefferson County. Shortly before the stonn dissipated it took a turn to the south-southwest and moved back into southeastern Clear Creek County about 22151. The stonn 's radar echo signature and the observation oflightning ceased between 2230L and 23001. The stonn's duration from inception to dissipation was about 4 hours and 30 minutes though its Virginia Canyon basin duration of75 minutes was about average for high elevation stonns reported in Henz, et al, 1989 and Henz, 1990. The track of the storm covered approximately 55 miles and the general diameter of the precipitating portion of the storm varied from 3 to 7 miles in size. The most intense precipitation core of the stonn as it passed over Idaho Springs was about 2-3 miles in diameter. Recent research (Jarrett, 1989 and Tunnell, 1990) of Front Range flash floods has stressed the occurrence of events at altitudes below 7,500 feet MS1. In fact recent National Weather Service policy indicates that flash flood warnings should be limited to elevations below 7,500 ft. in Colorado. The terrain covered by this stonn varied from about 8,300 ft. at its inception over Grand County to almost 14,000 ft. as it crossed the Continental Divide. 5