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

..

II
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
II
I
I

"~!..'-'

strong thunderstorms, Portions of the Buffalo Creek drainage basin were
affected by a thunderstorm between 720PM and 825 PM. Storm movement was
to the east northeast at 07-11 mph.

Of the additional storms studied only the strong storms of August 23, 1996
produced significant flooding on the basin, A quick review of Figures 10-14
shows that most of the storms did not produce significant aerial coverage or
depth of rainfall in the basin, Clearly, the storms of August 23, 1996 were the
most notable of the group, The first storm of June12, 1996 which has not yet
been analyzed may also offer additional insight into the factors which determine
which storm is capable of producing flooding on the basin.

The meteorological characteristics of the storms is summarized in Table 3
and shows significant differences in the structure of the atmosphere for'the other
storms dates compared to July 12, 1996, Note the highlighted conditions
associated with the August 23 storm comes the closest to matching the intensity
of storm updraft and depth of the warm layer in the updraft, Both storms moved
slowly in a very moist atmosphere, ,The initial review of these conditions
suggests that the following three factors may be useful in predicting basin flash
flood watches by the National Weather Service:

1. PWI is greater than 1.00" and
2. Storm updraft warm layer is greater than 1,5 km and
3. Cloud layer winds favor movement less than 15 mph
4. Predicted peak 3D-minute rain rate is greater than 1.00"

Table 3

Comparison of meteorological characteristics of Buffalo Creek
storms

DATE (1996)

PWI

STORM UPDRAFT STORM STORM SPEED OF
WARM LAYER UPDRAFT t.T MOTION/DIRECTION

PEAK 1/2 sq,
MI.12MIN,
RAINFALL
0,05"
1,14"
0,24"
0,16"
" O;52'~
0,35"

JUNE 12' 1,04" 0,7 km 3,5 'C 14-19 MPH/NE
JULY 12 1,39" 2,8 kmM'Qi, J5~1d~MpHE'
AUGUST 7 0,91" 0,9 km 3.5 'C 12-18 MPH/E-SE
AUGUST 8 0.92" 1,1 km 4,5 'C 08-12 MPH/N
AUGUST23 1,14" 1.7km'3.5'Q'[i',iiJ; ;.0,4~()8MPH/NE
SEPTEMBER 14 1,00" 1,5 km 2,0 'C 07-11 MPH/E-NE

'Second of two storms that moved over portions of the basin

A further comparison of the rainfall characteristics of the storms sheds
additional light on the differences which may help determine which storms are
capable of flash flooding the Buffalo Creek basin, Table 4 shows comparisons
of the basin average rainfall and the aerial coverage of rainfall in the basin.
Clear differences appear between all storms and the July 12 storm. The storms

24

PEAK 1/2 sq,
MI. 30 MIN,
RAINFALL
0,06"
3.42"
0,32"
0.42"
1,,36:'
0.43"