FLOOD00626

• County: Larimer
• Community: Fort Collins
• Title: An Analysis of Rainfall for the July 28, 1997 Flood in Fort Collins
• Date: 2/1/1998
• Prepared For: State of Colorado
• Prepared By: CSU
• Floodplain - Doc Type: Flood Documentation Report

Remarkably, no fatalities were reported. A summary of rainfall and runoff from this huge
storm is being prepared by the Colorado Water Conservation Board in Denver. Other very
heavy rains occurred in Phillips and Elbert Counties. Heavy local downpours continued in
early August and caused more local flooding, most notably in southeastern Colorado. A
Presidential Disaster Declaration resulted (DR-I I 86-CO) which eventually included a total of
13 counties in eastern Colorado. This report focuses only on the rains of July 27-28, 1997 in
and near Fort Collins.

Data Collection

In order to thoroughly document the rainfall patterns from the July 27-28, 1997 storms in the
Fort Collins area, an intensive effort was made to obtain rainfall information from any
potential source of data. Under ideal conditions, the effort to collect precipitation data would
have begun early on the morning after the flood. However, due to the widespread flood
damage on the Colorado State University campus, including minor damage at the official
weather station just north of the severely damaged Lory Student Center, and due to personal
emergencies associated with the flooding, and the nearly continuous barrage of media calls
and contacts from many sources seeking information about the flood, a systematic effort to
collect data did not begin until July 30th. The Colorado Climate Center had previously
performed an intensive survey of precipitation in 1994 as a part of a special radar-rainfall
research project (Clement et ai, 1995), so some expertise in storm surveying existed.
Unfortunately, no systematic plan had been developed to help guide a rapid and coordinated
data collection effort of the magnitude needed to survey this storm.

A data collection effort was hastily initiated. The following methods were used to obtain
precipitation data.

I) National Weather Service Stations. The National Weather Service (NWS) maintains a
national network of several thousand temperature, precipitation and snowfall
measurement sites or sites that measure only precipitation. Ten of these cooperative
weather stations are in Larimer County including the official Fort Collins weather station
on the CSU campus. These data are routinely transmitted to the National Weather
Service in Denver at the end of each month and were used in this study.

2) Mountain States Weather Services volunteer observers. For the past 20 years, nm
Wirshborn, director of Mountain States Weather Services (MSWS) in Fort Collins, has
maintained a network of volunteer weather observers in Fort Collins, Larimer County and
surrounding areas. Many of these observers call in precipitation reports to MSWS during
and after each significant storm, and most of them record 24-hour precipitation totals on
observation forms that are mailed in at the end of each month. These data were all
provided to the Colorado Climate Center in early August to assist in the storm
documentation. A total of 44 rainfall reports were included from MSWS volunteer
observers who fill out observation forms A few of these were redundant with NWS
reports. Other reports from MSWS spotters were received by phone.

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