<br />
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<br />1500' ./''''...AOOO
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<br />\, u _ ...,...' \..~_, 1
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<br />~<:-;I '--) Glen ,,-
<br />,f/ /Jjl'enl rak
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<br />~? / Eli. "r!
<br />/ Grand ',- I'lIrk '
<br />I L~l<e .......\l!'
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<br />10000' 10000' " './ / " \ '---
<br />, \ '-...... / ,\ "
<br />I \ ) / ~eckefs " \"
<br />", I I,' \. '"
<br />I , I ", l / ,/ \, Llrkspur
<br />111km2U 30 "',) l/ 75'00'
<br />
<br />G~end"vey
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<br />,'-----------~-
<br />
<br />.Windso'
<br />
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<br />,
<br />
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<br />
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<br />
<br />'Br;g~lon
<br />
<br />____o,Elbert
<br />"
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<br />
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<br />
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<br />\, U
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<br />............:.6006'--------'
<br />/ /
<br />/ ,
<br />/ ,/
<br />\
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<br />5000'
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<br />
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<br />5000'
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<br />
<br />_Elb!rt
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<br />
<br />b
<br />
<br />Figure 31. Local scale surface analyses. Frontal positions and reported winds are in black; Limon
<br />radar echoes are shown with VIP Levell return shaded gray, level 2 shaded orange, and level 3
<br />shaded black. (a) 2330 GMT, 31 July 1976. (b) 0000 GMT, 1 August 1976.
<br />
<br />while the western portion moved over the
<br />foothills southwest of Boulder. Rainfall
<br />amounts, however, were much less than
<br />those observed 20 to 80 mi to the north.
<br />~10reover, the echoes west and south of
<br />Boulder moved westward almost to the
<br />Continental Divide, indicating that they
<br />were not strongly affected hy the terrain. It
<br />seems likely that the trailing front became
<br />quasi-stationary between Denver and the
<br />foothills south of Boulder; therefore the
<br />very moist, unstable air probably did not
<br />reach the elevated terrain southwest of
<br />Boulder.
<br />From Boulder northward, meteoro-
<br />logical conditions were very different. The
<br />trailing front had moved into the foothills
<br />shortlv after 2330 GMT, and convective
<br />cloud~ developed very rapidly. By 0000
<br />GMT a few echoes were detected by radar,
<br />and by 0030 GMT several strong thun-
<br />derstorms were oriented in a north-south
<br />
<br />36
<br />
<br />line along the foothills. Many residents of
<br />the Ft. Collins, Loveland, and Longmont
<br />areas reported strong easterly or southeast-
<br />erly winds and low clouds moving rapidly
<br />into the foothills. Cloud bases were esti-
<br />mated to be at 7000-9000 ft MSL (2.2-2.7
<br />km). Surface winds at Ft. Collins and
<br />Greeley remained southeasterly until
<br />around 0400 G:\<IT after which the wind at
<br />Ft. Collins shifted to the northwest. The
<br />time series at Table Mountain shows that
<br />strong easterly flow persisted ,uter passage
<br />of the trailing front with a maximum east-
<br />erly component exceeding 20 m s-1, 400-
<br />600 m above the smface. The surface east-
<br />erly flow was temporarily interrupted
<br />around 0100 G:\<IT by a shallow region of
<br />westerly winds. This was probably weak
<br />outflow from the large cell located a few
<br />miles to the west of the site.
<br />Using the afternoon rawinsonde data
<br />from Sterling, Denver, and Grand Junction
<br />
|