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<br /> <br /> <br /> <br />10 <br />heavy rainfall, time series data at observation sites, <br />cartographic maps, etc.) are also available. The ASCII <br />grids of point estimates are the basis of the PFDS <br />interface results and are available to be downloaded in <br />a GIS compatible format. Figure 5 presents the <br />precipitation frequency table. The 24-hour duration, <br />100-year recurrence interval is highlighted in red. The <br />numbers in parentheses are the upper and lower <br />bound of the 90% confidence limits. <br /> <br />Figure 5: Precipitation Frequency Table <br />The precipitation frequency data available in graphical <br />format includes depth-duration-frequency (DDF) <br />curves and precipitation frequency curves with 90% <br />confidence limits. Figure 6 presents the precipitation <br />frequency curves. <br /> <br />Figure 6: Graphical Precipitation Frequency Curves <br />Precipitation frequency estimates from NOAA Atlas 14 <br />are point estimates, and reductions should be applied <br />when used for areas. The conversion of a point <br />estimate to an areal estimate is usually done by <br />applying an areal reduction factor, obtained from a <br />depth-area-duration curve, to the average point <br />estimates within the subject area. Currently, the <br />depth-area-duration curves from the U.S. Weather <br />Bureau’s Technical Paper No. 29 can be used for this <br />purpose and is recommended by NOAA Atlas 14. The <br />NWS is investigating the areal reduction factors for <br />NOAA Atlas 14 and may issue new areal reduction <br />factors in the future. <br />Probable Maximum Precipitation Events <br />The PMP, as defined in the HMR documents, is <br />“theoretically, the greatest depth of precipitation for a <br />given duration that is physically possible over a given <br />size storm area at a particular geographical location at <br />a certain time of the year”. No recurrence interval is <br />assigned to the PMP. <br />For Colorado, Montana, Utah, and Wyoming, the PMP <br />east of the Continental Divide is derived using the <br />methodology in HMR 55A; the PMP west of the <br />Continental Divide is derived using HMR 49 or HMR 57. <br />The PMP studies developed by NOAA and NWS are <br />shown in Figure 7 by geographical location in the <br />United States and are available online through NOAA. <br /> <br />Figure 7: Available PMP Studies <br /> <br />