A high pressure ridge off the coast of California has turned off the tap that provided above average moisture to the Sierra Nevada during December.A graph issued by the National Weather Service this afternoon comparing this year's snow water equivalent and the 30-year average for the Sierra Snow Lab near Donner Pass."The water year started out fairly average through the first half of December, then snow water equivalent rapidly increased above average for late December," forecasters said. "There has been very little additional accumulation since the end of December and now the region is anomalously low."Totals vary from one part …