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001673 f1 ow into Lake Powell for the remai ni ng months through July, pl us the long-term average natural flow into Lake Powell for August and September. This quantity is then reduced by subtracting the water depletion scheduled to occur in the Upper Basin throughout th,~ fore- cast peri od. Special Limit~tj~~~ Some limitations are applied to the procedure described above. In June, the magnitude of the forecast error is computed as in previous months; howl~'l'~r, it may not exceed 50 percent of the May forecast error. In July, the forecast error is simply 25 percent of the June forecast error. 7.1.2 Lake Mead Forecast The operation of Lake Mead and Hoover Dam requires a runoff forecast in each month from January through July. Flood control operation of Lake Mead requires use of the maximum forecast. The maximum forecast is defined by the flood contror-criteria for Lake Mead as the esti- mated inflow volume that, on the average, will not be exceeded 19 times out of 20. The CRSM first develops a mean monthly forecast for Lake Mead by taking the Lake Powell current month through September forecast, subtracting the portion which is forecast for August and September, and adding the long-term average natural tributary inflows between Lake Powell and Lake Mead for tht! current Inonth through July period. No additional error is incorporated into the Lake Mead forecast. The maximum forecast is then determined by adding an additional quantity, a constant, to the mean forecast. Seven constant values are supplied by the CRSM control file that correspond to the seven forecasts frorn January through July. The quantities presently used for determining the maximum runoff forecast for Lake Mead are listed below. Forecast period Quantity added to the Lake Mead mean forecast to determine maximum forecast (millio_n_ .a_cre-feet) January February March April May June - July - July - July - July - July - July July 4.980 4.260 3.600 2.970 2.525 2.130 0.750 30