FLOOD02053

• County: Weld
• County: Boulder
• Community: Weld, Boulder Counties
• Stream Name: Big Thompson River
• Title: Meteorological Aspects of the Big Thompson Flash Flood of 31 July 1976
• Date: 7/1/1977
• Prepared For: State of Colorado
• Prepared By: NOAA
• Floodplain - Doc Type: Flood Documentation Report

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'. Figure 2.s.~MC-I.FMl(prticilyill)alysis (orange) f.or 0000 GMT, 1 August 1,976. Synoptic s.urfac:e
,,',~I "nil lysis ar,d 500 .mb height analy~is are In blilF~' ~ositio~,pt the,)mppr;!ilnt ~oo.!"b short W"\I~ is
"0:: ..,alsoshowrl,in black.~ \1' 16.':>;; ~ 8&-' ~~'~<... ""
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sonde was released at approximately 2.315
GMT, prior to passage of the trailing front.
Tahle 2 compares soundings hlken
during the day of 31 July 1976. Note the
considerahle difference hetween the 1920
GMT Sterling sounding 'lIld the 0000 GMT
Denver sounding. Precipitahle water con-
tents were ahout 50% higher 'It Sterling.
While the Lifted Condensation Level
(LCL) was much lower at Sterling (780 vs.
630 mb), the Denver air mass needed only

30

10 mh of additional lift to reach the LFC.
This is in contrast with the air mass at Ster-
ling in which 140 mb ofhft was required to
attain the LFC. Diurnal cooling could be
expected to suppress the ongoing convec-
tion in the Denver area, and orographic
lifting would be required to trigger storm
development within the post-frontal air
mass that was moving into the foothills of
northern Colorado.
Denver and Dodge City soundings at