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<br />Pueblo on June 5. The first period of heavy thunderstomls occurred on the night oUune <br />2 on Dry Creek just upstream from Pueblo (see Figure 2). A bridge in Pueblo was <br />washed out at about 1100 pm as a result of this activity. The second period occurred on <br />the night of June 3 to the early morning of June 4 and it was dominated by two heavy <br />thunderstorm systems (see Figure 3). One system moved from northeast to southwest <br />and affected areas northwest of Pueblo. A second heavy thunderstorm moved out of the <br />southwest and merged with the first near Penrose, Colorado. The merged storm <br />subsequently moved to the southeast the evening of June 3 and affected points southwest <br />of Pueblo centered near Boggs Flat. Important topographic features which likely <br />contributed to reported merging of both thunderstOlw systems are shown in Figure 4. <br />Proposed thunderstorm tracks consistent with observations given by local residents are <br />also shown in Figure 3. <br /> <br />The focus of the present report is on the two heavy thunderstorms and the reported <br />merged system which led to the main flood the night of June 3. Property losses from <br />these floods exceeded $19 million, an enormous sum for 1921. Loss oflife was officially <br />listed as 78 but many additional people were washed downstream and their bodies never <br />recovered. <br /> <br />The meteorological setting that accompanied this flooding event was characterized by a <br />strong surface high pressure center over Alberta, Canada on June I. On June 2 a surface <br />low pressure center was situated over the upper Missouri Valley as the Canadian high <br />moved slowly southeastward reaching the northern part 0:" North Dakota on June 3. <br />Climatological Data from the u.s. Department of Agriculture suggest a possible cold <br />frontal passage through Colorado Springs to the vicinity of Pueblo on the afternoon of <br />June 2. The apparent storm motions, merger location, ;md motion of the merged storm <br />are consistent with the presence of a meso cyclone near Pueblo and a quasi-stationary <br />frontal boundary (see Figure 3). The merged storm, possibly a supercell, propagated <br />slowly along the frontal boundary probably under the influence of a weak steering <br />current. As the high continued to the southeast, eventually arriving over the Great Lakes <br />on June 5, an area of surface low pressure developed over western Arizona and remained <br />over the southern Rocky Mountain plateau for several days. This juxtaposition of surface <br />pressure features encouraged the development of strong easterly upslope flow along the <br />Front Range of Colorado. This fetch of moist low-level flow was apparently focused by <br />local topography into the foothills west and nOlihwest of Pueblo. <br /> <br />Follansbee and Jones (ibid) attribute this event to a series of cloud-bursts resulting from <br />"heavy rain-bearing clouds striking against the mountains and being deflected upwards". <br />Topography of the region (see Figure 4) evidently p]aycd a major role in focusing the <br />heavy convective storms nOtihwest and west ofPneblo. As seen in Figure 4, lhe line of <br />Front Range foothills forms a. triangular wedge westward to near Canon City pel111.itling <br />moisture inflow from the northeast and southeast:. <br /> <br />Statements of several residents who experienced this flood cited by Follansbee and Jones <br />(ibid) give credence to the hypothesis that two heavy thunderstonns actually merged into <br /> <br />6 <br />