FLOOD00419

• County: Jefferson
• County: Park
• Community: Buffalo Creek
• Title: The Buffalo Creek Flash Flood of July 12, 1996 Draft - A Reconstruction of Rainfall and Meteorology
• Date: 7/12/1996
• Prepared For: CWCB
• Prepared By: Henz Meteorological Services
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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Table 2

Comparison of radar reflectivity/rainfall rates from 530PM to
910PM on July 12, 1996 over the Buffalo Creek watershed.

"'GMT/PM, 2330Zl530pM 0025Z1625PM. iQ~:!l5Zl8n:5l?l\1I;; Q310Zl9.10PM'
: ' Radar peak 30~rTHri peak30.~min "~jfilR,aO:~mln; ,Pe~k::30~min
:.z . Level 2.25"', '.. 1;75!',. ,/, ,. ",,; ;,3;43~~:,';:: .,'2.79"
:: , 2 ',," , 0.17"/5min 0.11 "/5min O,22"/5min 0.17"/5min
> 3 0.23"/5min 0.15"/5min 0.30"/5min 0.24"/5min
4 , . 0.32"/5min 0.20"/5min 0.41 "/5min 0.33"/5min
.
5 0.45"/5min 0.29"/5min O,57"/5min 0.4 7"/5min
" 6 0.45"/5min 0.29"/5min 0.57"/5min 0.4 7"/5min
,
Warm Layer 2.7km 1.7km 2.8km 2.4km
..., PWI 0,90" 1,02" 1.31" 1.24"

Shortly after the second wave of storm ended, a group of severe
thunderstorms formed about 10 miles to 20 miles north of the basin near Golden
and Evergreen in central Jefferson County. These storms produced several
reports of 1,00-1.50 inch in diameter hail over central Jefferson County and brief
heavy rainfall as they rapidly moved east. Rainfall estimates in North Turkey
Creek Canyon were made by John Henz using a 4" diameter can which equaled
about 1.50 inches of rain in 22 minutes while the ground was covered by 1,25
inch in diameter soft hail. The NWS in Denver issued a severe thunderstorm
warning for this storm about 705PM.

While this storm was very intense, it moved east-southeastward at about
25 mph and cleared the Jefferson County foothills about 725PM, This storm
produced additional severe weather in western Arapahoe and northern Douglas
Counties between 730PM and 800PM. More importantly it produced a gust front
boundary of very humid northeasterly winds of 20-30mph which moved
southward into the Buffalo Creek watershed by about 800PM, This gust front
provided the meteorological mechanism which caused the Buffalo Creek
thunderstorm to go stationary over the watershed producing the flash
flood, The gust front acted as a focussing boundary for converging air masses
from the south and north, Both air masses were very humid and unstable and
provided the moisture for the flash flooding rainfall. The gust front is clearly
visible in the WSR-88D radar imagery and extended from Castle Rock in eastern
Douglas County westward to Buffalo Creek from 800PM until 900PM.

As the central Jefferson County storm moved north of Buffalo Creek,
additional storms were forming to the west. The Buffalo Creek thunderstorm
complex appears to have formed about 715PM along the slopes of Mount Blaine
and the Twin Cone Peaks in Park County 15-20 miles west of the basin, The
storm complex moved steadily eastward and into the central part of the Buffalo
Creek watershed by 808PM according the NWS WSR-88D radar data.

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