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Last modified
1/26/2010 2:27:44 PM
Creation date
10/12/2006 2:26:47 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
5000.125
Description
Flood Protection Section - Pikes Peak Early Flood Warning System
State
CO
Basin
Arkansas
Water Division
2
Date
10/29/1985
Author
John Henz-Ron Kelly
Title
The Denver Flash Flood Prediction Program - A Joint Hydrometeorological Effort - And Operational Prediction of the Denver Severe Hail-Rainstorm of 13 June 1984
Water Supply Pro - Doc Type
Report/Study
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<br />OOJ4u5 <br /> <br />plains mild moist plains air fed into the potential storm development <br />air on steady easterly breezes in the sub-cloud layer. In the cloud <br />layer a jet streak and double-wave mid-tropospheric disturbance were <br />poised to cross the threat region during the afternoon maximum heating <br />time of 1400-1800MDT. The cloud-layer shear structure favored the <br />development of hail production in superce11-type thunderstorms. <br /> <br />The devastating June 13. 1984. northwest suburban hail-rainstorm <br />was predicted very accurately by the Denver F2-P2, At 1130 MDT HKA <br />notified all six F2-P2 counties that two waves of heavy thunderstorms <br />would cross the Metro area between 1300L-1930L with hourly intensities <br />of 1-2 inches per hour and total rainfall of 2-4 inches. Additionally <br />large hail over 1.0 inch in diameter was expected with storm drain <br />clogging expected. Heaviest action was specified for northern Jefferson <br />County and western Adams County. <br /> <br />About 1330 MDT HKA notified Jefferson County that the first wave <br />of storms was forming in northwestern Jeffco foothills and that large <br />hail and heavy rain would cross Arvada, Wheat Ridge. northern Lakewood <br />and Westminster between 1400 MDT and 1530 MDT. Adams County was called <br />about 1335 alerting them to the rain and hail threat from 1445-1600 MDT. <br />In Jeffco. Clear Creek. Ralston Creek. Van Bibber and Little Dry Creek <br />were identified as likely flooders with 1-2 inches of rain. <br /> <br />About 1345 MDT Arapahoe County and Douglas County were alerted to <br />storms forming near Chatfield Reservoir and Sedalia which would produce <br />1-2" rain and 1-2" hail over the Highlands Ranch-Littleton area from <br />1415-1530 MDT. <br /> <br />Several additional storm updates were passed along to Jefferson. <br />Adams. Douglas and Arapahoe Counties over the next 1-2 hours as these <br />storms crossed these areas. The updates detailed storm intensity and <br />movement. <br /> <br />About 1500 MDT the second wave of storms began forming in the <br />northwestern Jefferson County foothills, By 1600 MDT these storms <br />were pounding Arvada. Wheat Ridge and by 1700 MDT Lakewood. HKA <br />notified Jeffco about 1500 that the second wave of storms would cross <br />the northern 1/2 of Jeffco north of Hampden between 1600-1800 MDT <br />producing 1-2 inch rains and up to 6-12 inches of peasize hail. Clear <br />Creek. Lena Gulch, Little Dry Creek and Lakewood Gulch as well as Green <br />Mountain were basins identified as likely flooders. Additionally Denver <br />County and Adams County were likewise warned of the storms' impact. <br />Concerns over possible tornado formation were discussed with Denver and <br />Lakewood. <br /> <br />8y 1715 MDT (Figure 6) the merged storms resembled a horseshoe <br />extending from Lakewood to Arvada to Thornton and east to Aurora. <br />Serious hail damage and flooding continued until about 1900 MDT when <br />the storms weakened and moved northward. The storms caused a significant <br />pattern of hail damage and heavy rains summarized in Figures 7 and 8. <br />Peak rainfall of 2.09 inches in one hour in Wheat Ridge was close to <br />the 30-50 year one hour storm intensity. while total rainfall peaked <br />at 4.75 inches. A more complete but preliminary summary of this storm <br />has been prepared by HKA and is obtainable from UDFCD. <br /> <br />-12- <br />
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