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<br />It is noteworthy that many similarities exist in the vertical temperature, moisture <br />and wind profiles of the historic flash flooding days. Surface temperatures were <br />generally in the 75 to 85 degrees F range with rather' high surface dew points of <br />58 to 65 degrees F, A deep moist layer extended from the surface to just above <br />500 mb or 18,000 feet. A strong low level jet of 25 to 50 mph was located in the <br />bottom 2,000 to 3,000 feet of this moist layer with wind speeds decreasing with <br />altitude but with decidedly upslope directional components to the wind fields, <br />Above the moist sub-cloud layer the air was much dl'ier from 18,000 feet to over <br />40,000 feet and wind speeds tended to decrease with altitude and remain <br />roughly parallel to the local topography, An upper level disturbance and/or <br />moist monsoonal flow were present in all cases to assist in triggering and <br />maintaining storm development. <br /> <br />At the bottom of Table 3 is a section on the CSM Output Rainfall, CSM refers to <br />the HMS Convective Storm Methodology reported in Henz (1995a, b, c) which <br />was developed to assist in the quantitative precipitation forecastin9 (QPF) of <br />flash flooding events. A copy of theSE! papers which describes the methodology <br />in detail is provided in Appendix B. Tile CSM uses the observed surface <br />temperature and dew point, the surface to 500 mb Precipitable Water Index <br />(PWI) and the observed atmospheric sounding to calculate the local storm <br />precipitation according to the following: <br /> <br />(1) Peak 50-minute rain ::: PWI times I;~~m!h of updraft warm laver times 2 <br />1.5 km <br /> <br />Note that the "doubling factor" operation is performed only if the depth of the <br />warm layer is greater than or equal to 1.5 Imn for elevations above 3,500 feet, <br />greater than or equal to 2.5 km for cleveltions bel,c)w 3,500 feet and greater <br />than or equal to 3.5 km for locations whelre the surface dew pI)int is 70F or <br />greater, If the depth of the warm layer is less than these values, the resulting <br />fraction in the equation is not doubled. For example, if the cloud base <br />determined on a Skew T, Log P diagram using the observed surface temperature <br />and dew point is 3.0 km and the surface lifted parcel cools to 0 degrees Celsius <br />at 5.0 km, then the depth of the warm layer is ~~.O km, <br /> <br />In Table 3 the observed surface temperature and dew points and the observed <br />soundings were plotted on a Skew T, Log P diagram for each of the extreme <br />precipitation events, The peak 60 minute rainfall was calculated using Equation <br />1 above. The peak 30 minute rainfall was computed as 70 percent of the peak <br />60 minute rainfall and the peak 10 minute rainfall as 60 percent of the peak 30 <br />minute rainfall. <br /> <br />11 <br />