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<br />In general, the quantifiable differences in the storm atmospheres are: <br /> <br />. Surface temperatures and dew points in CD-West storm atmospheres are both 10F <br />cooler on average than those observed in CD-East storm atmospheres. <br /> <br />. The 700mb to 500mb layer in the CD-West storm atmosphere is about 1-2 degrees <br />cooler on average than the CD-East storm atmosphere. <br /> <br />. The CD-West storm atmosphere PWI is 0.27 inches or 20 percent drier on average <br />than the CD-East storm atmosphere. <br /> <br />. Sub-cloud layer winds connecting low level moisture to storm updrafts in CD-West <br />storm atmospheres are 50 percent less than in CD-East storm atmospheresl <br /> <br />. The CD-East sub-cloud layer winds took the form of a "terrain-locking" low-level <br />jet. The CD-West sub-cloud layer winds took the form of transient surface frontal <br />or gust front winds. The CD-East sub-cloud winds favor heavier rainfall. <br /> <br />. Cloud shear in CD-East storm atmosphere takes the form of a strong inverse wind <br />shear with low level winds stronger than cloud layer winds. In the CD-West storm <br />atmosphere, the reverse is true with cloud layer winds almost twice as strong as <br />sub-cloud layer winds. CD-East winds favor heavier rainfall. <br /> <br />. The depth of the updraft warm layer is 25 percentdeeper(+ 0.7km) in the CD-East <br />atmosphere than the CD-West atmosphere. The deeper the updraft warm layer the <br />more efficient the cloud's warm rain efficiency. CD-East structure favors heavier <br />rainfall. <br /> <br />. The average CD-East storm total rainfall is estimated to be over 2.5 times the <br />average CD-West storm total rainfall. <br /> <br />These key differences present compelling differences in the storm atmosphere structure between <br />CD-West and CD-East storms that relate directly to the storm total rainfall estimates. These <br />differences argue for decreased site-specific PMP rainfall west of the Colorado Continental Divide <br />by at least a factor of two to one! <br /> <br />Considering the lack of low-level moisture from the Gulf of Mexico into the western storms, these <br />results are not surprising but provide key quantitative differences that should affect PMP <br />considerations and calculations, Except for these ,differences the CD-West and CD-East storm <br />atmospheres are remarkably similar. <br /> <br />Thus, a clearer picture of the atmospheric structure associated with extreme precipitation events <br />in Colorado has emerged that supports the following general characteristics: <br /> <br />1. A moist, warm but not saturated atmosphere with temperature-dew point differences of about <br />5C through the midlevels of the atmosphere. PWI average 1.00 to 1.25 inches. <br /> <br />2. Average to slightly below average surface temperatures and well above average surface dew <br />points. Surface dew points average in the 50's west of the Divide and 60F or more east of the <br />Divide. <br /> <br />3. The presence of an upper level disturbance at 500mb and a sub-cloud layer forcing feature, i.e., <br />gust front or surface front west of the Divide or a low level jet east of the Divide. <br /> <br />4. Low cloud layer wind shears with inverse speed shear, i.e., stronger sub-cloud layer winds than <br />cloud layer winds east ofthe Divide and the reverse west of the Divide, <br /> <br />5 <br />