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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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.

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, Unfortunately, its arrival and that of
the gust front from the earlier storm in central Jefferson County coincided, Radar
shows the storm going stationary over the lower half of the basin from about
815PM until about 900PM, It is very possible that the storm would not have
gone stationary if the gust front had not provided a focus for a strong inflow of
moist, unstable air into the storm complex, No impact of the fire burn 'areas on
the formation of this storm can be detected.

the peak rainfall production occurred from 815PM until 900PM over the
lower third of the basin. During this period over 3,00 inches of rain fell over the
lower third of the basin, The rain was accompanied by hail at times, especially
before 830PM. By 913PM the core of the storm had moved eastward over the
Spring Creek watershed which experienced the same amounts of rain as the
lower third of Buffalo Creek between 900PM and 945PM.

The HMS radar-estimated storm rainfall from 739PM until 913PM across
the Buffalo Creek basin shows the basin average rainfall during this period was
2.16 inches of rain with a peak 0.5 square mile rainfall of 5.13 inches. During
this period, an 18 square mile area of the lower third of the basin received over
3,25 inches of rain while a core area of 6 square miles just above the town of
Buffalo Creek was inundated by over 4 inches of rain and hail.

The July 12, 1996 storm total rainfall over the basin for the entire period
from 21 OPM until 1023PM shows the basin average rain increases to 2.49
inches while the peak 0.5 square mile increases to 6.29 inches, The lower
third of the basin shows an average rainfall of just over 4,00 inches. Clearly,
this thunderstorm rainfall was focussed by the stationary movement of the
storm over the basin for about 30-45 minutes.

Another contributing factor to the flash flood may have been the slow
movement down the basin of the rainfall core which could have aided in
producing a runoff maximum that traveled with the storm, This storm was the
only one which went stationary over northeastern Colorado. All the other
storm complexes moved at speeds of 25 to 40 mph while producing severe
weather. It appears that the gust front which aided storm intensification and
inhibited storm motion was a major contributing weather feature to the storm's
severity along with the very moist condition of the atmosphere,

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