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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />: I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />due to additional or more complete data from this later survey, in combination with our <br />interpretation of observational uncertainties. <br /> <br />A revised analysis of storm rainfall isohyets is shown in Figure 6. It is with a high degree <br />of confidence that we can say that there was an area of several square miles that received <br />in excess of 10 to 12 inches of rain in a period of6-8 hours, with the majority of that <br />rainfall occurring in the period from 7:30 PM to Midnight. The maximum rainfall of 15 <br />inches as originally reported is possible and was read and recorded diligently by the local <br />residents, However, there is a good chance that the observation was somewhat <br />exaggerated by ground splash. As a result of this change, we lowered this value to 13 <br />inches, although this is only an estimate, the area exceeding 14 inches shown in the <br />preliminary analysis cannot be confidently confirmed from the available rainfall reports. <br />The largest value is now believed to be somewhat less than 14 inches. While this revised <br />analysis shows less rainfall at the storm center, there is strong evidence that the rainfall <br />maximum extended farther to the west and south than originally thought with very heavy <br />rains extending southwestward to just north of the town of New Raymer. The analysis of <br />two separate areas in excess of twelve inches is somewhat arbitrary but is also suggested <br />from NWS radar analysis. <br /> <br />A secondary smaller maximum over northeast Weld County was confirmed but not to the <br />magnitude originally shown (14 inches). Quantitative data only support an estimated <br />maximum at this secondary center ofless than ten inches. From interviews with local <br />residents, it appears that this secondary maximum was a result of heavy rain earlier in the <br />afternoon of the 29th that may have begun as early as 3 :00 PM MDT far before rain began <br />farther to the south. The rains later in the evening were substantial in that area, but much <br />less than what was observed farther south. <br /> <br />While our re-analysis of the area and magnitude of heaviest rainfall resulted in a reduction <br />of the areas and the magnitude of the most extreme (12 inches and greater) values, the <br />inclusion of additional reports, plus the follow-up with many of the people surveyed last <br />year whose rain gauges may have been full to the top after the storm, suggests that the <br />areas that received more than six inches ofrain from the storm may, in fact, be more <br />extensive than originally thought over portions of Weld County and western Logan <br />county. From this analysis, the area receiving at least six inches of rainfall encompassed <br />approximately 270 square miles. This is a very large storm of this magnitude for <br />Colorado. <br /> <br />There had been concern prior to this evaluation, that many of the rainfall reports gathered <br />last year and shown as July 29-30 evening storm totals may have also included rain from <br />the evening ofJuly 28 and morning of the 29th. This was found to be much less of a <br />problem than expected, as nearly everyone queried had indeed observed and reported a <br />significant rainfall (generally 1 to 2 inches over the area and locally as much as 3" north of <br />New Raymer) from the storm on the evening of the 28th. In most cases, gauges were read <br />and emptied prior to the July 29th evening storm, so that the storm reports gathered by <br />the original survey teams were not exaggerated by additional precipitation from previous <br /> <br />27 <br />