FLOOD02473

• County: Weld
• County: Logan
• Basin: South Platte
• Title: A Post Evaluation of Rainfall Reports Associated with Pawnee Creek Flood of July 29-30, 1997 in Eastern Weld and Western Logan Countie in Northeastern Colorado
• Date: 8/1/1998
• Prepared For: Weld County/Logan County
• Prepared By: CSU
• Floodplain - Doc Type: Flood Documentation Report

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Stonn Rainfall
Location (inches ) July 28
T R Sec original verified Confidence Reason for change Rainfall
10 57 7 (??) 3-4 NA
7 59 (??) 0,5 B Additional data 2"
7 58 3 3.6 A Additional data 2.38
8 56 6 4 -4,5 B Additional data NA
9 57 10 11 C/O Just a guess NA
9 57 18SE 8.5+ B/C Gauge spilled 3.5
9 56 34 5 B Additional data NA
8 56 14 2.6 A Additional data 1.75
11 55 30 5-6+ C Additional data NA
12 55 34 3.59 B Additional data NA

Based on this rainfall survey and post-evaluation for the Pawnee Creek flood event ofJuly
29-30, 1997, it was confirmed that near the core of heaviest precipitation, rain began
about 7:30 PM and lasted until after midnight. The total stonn duration was as much as 8
hours, but the great majority of precipitation fell in six hours or less. Southwest of the
stonn center, the rains began a bit later -- perhaps 8:30 PM or even later -- as new cells
developed on the southwest flank of the stonn. Farther to the north over extreme
northeastern Weld County, a significant amount of precipitation also fell in the late
afternoon, before the main event developed farther to the south.

Reports suggest that there were no incredible rainfall rates (in excess of three to four
inches per hour) but rather heavy rainfall that persisted much longer than in more typical
intense Colorado thunderstonns. There was little or no hail reported with the storm, and
many observers independently reported the lightning as frequent but not extraordinary and
more like sheet lightning.

A map of point rainfall reports was produced (Figure 5). Keep in mind that only those
reports in Weld County and extreme western Logan County were reviewed during this
survey. By comparing this to the results of the original stonn survey and draft document
of October 1997, some differences in rainfall values are apparent. For example, a few
inconsistencies were found in reported rainfall amounts between the data tabulation
prepared by the CWCB in 1997 and the rainfall totals plotted on preliminary rainfall maps.
Weare choosing in favor of the values reported to us this year, if different from what was
noted last year and if evidence suggests that the entries made last year were inaccurate,
There were also a few inaccuracies in station location, and some rainfall reports gathered
last year that could not be confinned in this post evaluation. Most changes, however, are

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