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<br />Presentation by Mr, John Henz
<br />Orographic effects - extended storm sample, Orientation of isohyetal pattern and cloud layer winds for extreme precipitatio
<br />events, Observed orographic barrier moisture depletion for extreme events, The expanded fmal storm set included the (1)
<br />1965 Plum Creek, falcon, Holly (2) 1935 Cherry Creek, Hale (3) 1976 Big Thompson (4) 1972 Rapid City (5) 1969 Big Elk
<br />Meadow (6) 1981 Frijoles Creek (7) 1997 Fort Collins and Pawnee Buttes (8) 1921 Penrose,
<br />Key points form extended sample were:
<br />. all storms support that the axis of the isohyetal pattern +/, 10 degrees of cloud layer steering winds
<br />· all with sub-cloud layers winds greater than 25 mph feeding the updrafts and 50-90 degrees to the right of the steering cl
<br />layer winds,
<br />. All storm event inflow occurred with 1,350 feet to 3,00 feet oftopographic lift within 150 miles except Hale (200 feet)
<br />and Holly (300 feet), Implication: Hale and Holly not orographic events,
<br />. Ratio of the event extreme rainfall to Surface to 500 mb Precipitable Water Index ranges from 10:1 to 24:1.
<br />. Importance to the Site Specific PMP, Our study is storm based, steering winds for a stressing Cherry creek event should
<br />be along the basin or roughly north south orientation, Thus love level inflow winds should be from the east to southeast
<br />based on observations, This implies that storms with these wind flow fields are best suited for transposition into basin
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<br />Look at the orographics inflow lift area for the extreme events, Palmer Ridge events (Cherry Creek 1935, Plum Creek 1965)
<br />Southern Colorado events (Penrose 1935, Frijoles Creek, 1981), Foothills events: Big Thompson, Rapid City, Cheyenne
<br />Ridge events, Cheyenne 1985, Pawnee Buttes 1997, Plains events: Hale 1935, Holly 1965,
<br />Some key observations:
<br />Hale and Holly look different.
<br />. Lift may have been provided by stationary fronts,
<br />. Other events feature 1,400 to 3,500 ft oflift, ]
<br />. The Cheyenne Ridge events featured a rotating severe storm on the ridge and a low level jet southeast wind on the
<br />other but relatively little lift,
<br />Orographic barrier depletion
<br />. Used observed changes in the PWI (NCEP) and surface dew points form Colorado Springs area to Denver area,
<br />. On June 16, 1965 a 46% moisture depletion was observed form Colorado Springs to Denver
<br />. On June 17, 1965 a 28% moisture depletion was observed,
<br />. Changes in saturated PWI from Colorado Springs to Denver 25,35% decreases
<br />. This information will support the barrier moisture depletion application in our SSPMP calculation,
<br />Almost ready for prime time inputs
<br />. Orientation of storm along axis of the basin from south north implies south north cloud layer steering winds
<br />. Based on above low level winds are east to southeast at 25,40 mph based on storm event observations
<br />. Hale and Holly were not orographic storms compared to all others in the storm sample, They are truly plains storms anc
<br />very different
<br />. Orographic moisture depletion observed during events with storm east to south winds was 25,46%,
<br />. Multiple precipitation centers favored over "bullseye"
<br />Not ready for prime time results
<br />. Storm spacing downstream of Pikes Peak the missing link storm pattern is not conclusive enough to exonerate Cherry
<br />Creek from a big storm,
<br />. However demonstrates strong promise given additional documentation as a repeatable orographic effect.
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<br />Presentation by Mr. Doug Trieste
<br />. The objective of his research and presentation was to determine flood hydrographs and maximum Cherry Creek
<br />Reservoir elevations from critical historic storms transposed over Cherry Creek Basin, Mr, Trieste presentation was
<br />centered around the storm transpositioning analysis and its effects on the possible PMF for storms critically centered in
<br />the Cherry Creek Drainage Basin, The following are excerpts from his presentation,
<br />. Process: Obtain critical storms that are transpositionable into the Cherry Creek Drainage Basin, These storms are rotate
<br />and centered in the basin, the pattern is clipped to the basin boundary, and then the storm is maximized in.place to obtair
<br />the greatest rainfall values, using NWS maximization methods, The critical storms used were,
<br />Flood Protection. Water Project Planning and Financing. Stream and Lake Protection
<br />Water Supply Protection. Conservation Planning
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