FLOOD10403

• County: Statewide
• Basin: Statewide
• Title: Colorado's 1997 Flood Season In Review
• Date: 8/1/1998
• Prepared For: CWCB
• Prepared By: Riverside Technology, Inc.
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Meteorology for the 1997 Flood Season

2.0 Meteorology for the 1997 Flood
Season

The summer of 1997, particularly the months of July and August, will be
remembered for the extreme precipitation experienced in Colorado and
along the Front Range. The State of Colorado, among other states in the
southwestern United States, experienced an unusually strong influx of warm,
moist air from the south that contributed to a number of extreme
precipitation episodes. A brief description of the large-scale meteorological
conditions present in the state during the summer in general, and during the
end of July and early August in particular, is provided here and is based
primarily on two resources: The Fort Collins Flood: Atypical Rainfall and
Runoff Complexities (Forecast Systems Laboratory 1998) and An Analysis of
Rainfall for the July 28, 1997 Flood in Fort Collins, Colorado (Colorado State
University, Department of Atmospheric Science 1998).

2.1 Genera I Meteorology

The month of May displayed near average precipitation across much of the
state except for western Colorado, which experienced above average
precipitation. Early June exhibited typical early season atmospheric
instability that manifested itself in several large, localized precipitation
events in northeastern Colorado on June 2, June 6 through 7, and June 14
through 15, as well as a tornado in Boulder on June 6. South-central Colorado
also experienced several large localized precipitation events. One such event
occurred at the Colorado Springs/Fountain Creek area from June 13 through
14 where up to 5 inches of rain may have fallen in the span of 2 hours
(Doesken 1998a). June was wetter than normal in much of the state, with
most of the precipitation occurring during the first 2 weeks, while the last 2
weeks in June were dry across much of the state.

July was wetter than normal across much of the state. Beginning in mid July,
the state experienced a gradual increase in atmospheric moisture caused by
the unusually strong influx of warm, moist air from the south. 1his influx of
tropical moisture continued throughout the summer and slowly trailed off
by the end of September. Atmospheric moisture was enhanced sharply on
July 27 and 28 when a cold front and high pressure area over the northern
plains pushed moisture from the plains westward into eastern Colorado
(Doesken 1998b).

The flood season ended with some unusually large precipitation events
during the month of September. Extreme precipitation in northwestern
Colorado from September 18 through 21 caused the Elk and Yampa Rivers to
reach near flood stages. Four-day rainfall totals for this period in
northwestern Colorado were on the order of 4 to 8 inches and were some of

d479/chap2.doc 08/12/98

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