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<br />FORECAST COMPARISON <br /> <br />RTi's primary approach for investigating the forecast discrepancies was to develop a monthly water <br />balance for the RlODELCO forecast point. The intent was to identify the major water balance terms and <br />then compare across years to identify discrepancies that may have contributed to the forecast enors. <br /> <br />The water balance terms include: <br /> <br />· Precipitation: RTi calculated monthly estimates of basin average precipitation from the PRISM <br />grids. <br /> <br />· SWE accumulation or ablation: RTi calculated the total monthly accumulation or ablation of SWE <br />from SNODAS. Figure 4-1 shows the average SWE depth across the RIODELCO basin calculated <br />from SNODAS for the available period of record. <br /> <br />RIODELCO SNODAS SWE <br /> <br />20 <br />18 <br />16 <br />'2 <br />...... 14 <br />.s:: <br />- <br />a. 12 <br />Q) <br />C 10 <br />w <br />3: 8 <br />en <br />~ 6 <br /><( 4 <br /> <br />2 <br />o <br /> <br /> <br />- WY2004 <br />- WY2005 <br />WY2006 <br />- WY2007 <br />- WY2008 <br /> <br />o m ro ~ w ~ ~ ~ N ~ 0 m ro ~ w ~ ~ ~ N <br />N ~ ~ ~ m ~ ~ ~ ~ m ~ N ~ W ro 0 N ~ W <br />~ ~ ~ ~ ~ N N N N N ~ ~ ~ ~ <br /> <br />Day In Water Year <br /> <br />Figure 4-1. Average SWE Depth above RIODELCO from SNODAS <br /> <br />· Sublimation: RTi utilized the KALS climate data to identify four months (i.e., May 2004, April <br />2005, June 2005, April 2008) that were likely to have high sublimation potential based on high winds <br />and low humidity. In an inspection of the SNODAS sublimation products during these four months, <br />the blowing snow sublimation term from SNODAS was determined to be localized and not a <br />significant water balance component. However, the surface sublimation and condensation term is <br />significant. Therefore, RTi processed the surface sublimation grids for March to July of each water <br />year and included surface sublimation in the water balance calculations. <br /> <br />· Rain plus melt: This term is the net moisture that reaches the soil from the snowpack as melt or <br />directly as precipitation. Rain plus melt is computed as the precipitation minus two loss terms to <br />SWE accumulation and sublimation. Rain plus melt is limited to a minimum value of zero in months <br />when the SWE accumulation calculated from SNODAS is larger than the monthly precipitation value <br />calculated from PRISM. <br /> <br />4 <br /> <br />~Riverside Technology, inc. <br />