Lake Tahoe's level is falling nearly twice as rapidly as normal and the man in charge of monitoring the lake's ups and downs says he is not exactly sure why. Federal water master Garry Stone said the lake is falling at a rate of nearly a quarter of an inch a day and has declined one-half foot in the last month. Stone said that amounts to the loss of about 2,400 acre-feet of water a day. He said the discharge from the lake into the Truckee River is only 672 acre-feet daily and that the rest is being lost through evaporation. The weather has been hot and windy recently and Stone said that could have something to do with the rapid drop.