FLOOD05189

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Basin: Statewide
• Title: Survey of Thunderstorm Rainfall Characteristics - 1979 to 1988
• Date: 9/1/1989
• Prepared For: CWCB
• Prepared By: Henz Kelly Associates
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Table 4 5 minute and cumulative thunderstorm rainfall
calculated from average survey characteristics using
the H~A Excessive CDnvective Rainfall Model fDr three
storm types.

Storm A

Storm B

StDrJII C

Front-end dumper

Multi-cell train

Middle-dumper

Time 5 min Cum 5 .in CUJII 5 min CUJII
05 .25 .25 .50 .50 .05 .05
10 .50 .75 .50 1.00 .10 .15
15 .35 1.10 .60 1. 60 ,10 .25
20 .40 1. 50 .40 2.00 .15 .40
25 .50 2.00 .25 2.25 .15 .55
30 .25 2.25 .25 2.50 .30 .85
35 .15 2.40 .10 2.60 .30 1. 15
40 .15 2.55 .10 2.70 .45 1. 60
45 .10 2.65 .05 2.75 .45 2.05
50 .15 2.80 .25 3.00 .45 2.50
55 .10 2.90 .25 3.25 .45 2.95
60 .10 3.00 .50 3.75 .30 3.25
65 .15 3.15 .50 4.25 .30 3.55
70 .30 3.45 .50 4.75 .15 3.70
75 .15 3.60 .25 5.00 ,15 3.85
80 ,20 3.80 .25 5.25 ,10 3.95
85 .30 4.10 ,15 5.40 .10 4.05
90 .15 4.25 .10 5.50 .05 4.10
95 .10 5,60
100 .15 5.75
105 .10 5.85
110 .15 6.00

Figure 7 shows a cOJllparisDn of the 5 minute rainfall profiles of
the three storms while Figure 8 shows a comparison of the three
storms' cumulative rainfall profiles. Each of the storms is
assumed to COlver an area of 50 square miles with the rainfall
profile. Henz, 1974 indicated that the average severe foothills
thunderstorm's radar size of the raining area was 145 square miles
with a 16 square mile peak rainfall CDre moving at a storm average
speed of abDut 10 mph.

The three storm rainfall prDfiles are cDnsidered to be reasonable
but have not been assigned return frequencies. It is possible
that 2-3 severe thunderstorms a year may occur in the central
CDlDradD PrDnt Rsnge between April and September that meet the
characteristics of Storms A and C. Storm B, the multi-cell storm,
represents a less common storm type that would fall between StDrms
A and C and the Big Thompson Storm Df 1976.