FLOOD08366 - Laserfiche WebLink

Home Browse Search

\,fOJ \ ". . o Map: the placement of the NWS 21" storm center; the NWS chronology given in 1999 shows the peak 6-hour rainfall amount being 15.45 in Figure 7c of the report, o Map: the Plum Creek storm over the CC Basin as compared to Ihe NWS 21, inch center and the comparison of the locations of the maximum rainfall, o Map: the "missing link" storm over the NWS 21-inch center shows that the peak rainfall centers are still in the upper part of the CC Basin and the "missing link" storms results in much less rainfall being introduced into the basin, o Mr. Lou Schreiner mentioned, at this point, that the NWS centers the design storm in the basin for maximization ofthe rainfall amounts, o Chart: the May 30-31, 1935 storm event - chronology of the different centers for that particular storm, o This chronology suggests that the A and D cells were created due to different factors to begin with; the A cells were probably due to topographic influences and the D cells were due to a warm frontal overrunning by a strong low level jet; these tow centers were not connected to each other meteorologically due to the fact that Ihey were occurring at the same time al certain periods in the storm's total life cycle; because of this, the Hale center may not be transposable into the CC Basin, o Chart: Comparison of the hourly rainfall first reported by Ihe NWS in the first study (21 inches) and the 15.45-inch amount given at the 1999 meeting; Chart: displaying all the different storm centers as compared to the NWS amounts of21 and 15,45 inches, o The NWS storm peaks are around 10:00 while all the other storms peak at earlier times; no other historical storms fit into this temporal pattern; Mr. Schreiner stated that the NWS has never used this idea of storm timing, but did suggest that this idea be studied further. o The A-3 storm center of 10.5 inches appears to be out of place with the rest of the rainfall center amounts; especially if one takes into accounl that morning precipitation may have added to this total amount that was initially reported as a one-hour rainfall amount (the horse trough center), . Presentation bv Mr. Brian Rappolt: Mr. Rappolt was tasked 10 call different government agencies t find out what they used as parameters for the antecedent rainfall condition, The following are his results: o Colorado - HMR 56 is followed and NWS Hydro 45; 100 percent ground saturation is assumed and reservoir storage is considered to be full, o Mr. Alan Pearson stated that Colorado also follows HMR 52 and 53, the Bureau of Rec1amation flood hydrology manual, and PMF hydro graphs, o New Mexico - uses HMR 55a; Arizona - HMR 49; Wyoming - HMR 49; Montana - HMR 55a, o USACE - HMR 55a; FERC - in,house procedures, 4