FLOOD05944

• County: Saguache
• Basin: Rio Grande
• Title: Radar - Rainfall Reconstruction of the Saguache Creek Flash Flood of July 25, 1999
• Date: 6/1/2001
• Prepared For: Saguache County
• Floodplain - Doc Type: Flood Documentation Report

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Figure 8 shows the time and intensity distribution of the storm for the basin
average rainfall and the eastern and western portions of the sub-grid where the
heavy rainfall occurred. Note that over 90% of the rain fell in just less
than two hours though the entire storm lasted three hours. The west
basin rainfall maximum preceded the east basin's maximum by about 20 minutes
while the maximum value of the east basins rainfall was slightly larger.

The storm rainfall began over the basin at approximately 228PMMOT and lasted
until 524PMMOT. The peak rainfall in the west basin occurred from 330PM MOT
to 345PM MOT while the east basin peaked from 405PM to 440PM in a singular
and longer peak.

4.0 Cloud to Ground Lightning Data

In order to better examine this particular event, Cloud to Ground
Lightning Oata (CG) was analyzed in with respect to both the topography and
the reflectivity/rainfall pattern. CG data was acquired from the National Weather
Service's (NWS) National Lightning Oetection Network (NLON) through its
contract operator, Global Atmospherics, Inc. (GAl). HMS obtained CG data for a
24-hour period for a circular area with a 25-mile radius centered on the affected
flooded area near Saguache. The CG data was then parsed according to
whether or not it struck within, or very near, the grid area defined in the rainfall
estimation section. (See Figure 9)

The data was re-plotted, using the latitude and longitude of each CG
strike, for 15-minute segments starting at 2115 UTC (3:15 PM MOD and ending
at 2245 UTC (4:45 PM MOD for the grid area, which can be seen in the
Appendix. The grid located CG data was divided up into 5-minute segments
corresponding with the radar reflectivity images available. A total of 274 CG
strikes were detected in or near the grid for the entire duration of the event.
The distribution of the CG strikes was separated into 5-minute segments and the
temporal distribution for these strokes in the grid. The peak 5-minute count of
grid-based CG strokes (34) occurs in the time interval from 2204UTC to 2209UTC
(4:04 to 4:09 PM MOD.

4.J CG Data and Topography

Spatial-temporal analyses of the CG lightning data with respect to
geography and topography were also made to study any possible impact
topography made have had in the CG distribution. Comparisons of the grid
topography and CG strike locations show that in the first 15 minute period of
notable lightning activity (2130-2145 UTC), that over half of the strikes were on
the east side of the Middle Creek valley while other strikes were fairly scattered
in nature. These strokes also did not show any particular favor towards the
elevation at which they struck.

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