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 of the central Sierra to another, forecasters said the trend is shared for all locations.
"In general, strong high pressure has been situated off the coast of California since the beginning of January with only a few transient storms moving through," according to the report. "Ridging is disrupting the flow of moisture that would feed any storm systems moving through California and Nevada."
The picture going into March isn't much brighter, with long-term models indicating drier than normal conditions.
According to Natural Resource Conservation Service snow telemetry, the Carson River basin dropped down to 94 percent of average as of Monday morning. Carson Pass and Spratt Creek snow sites still show better than average snow water equivalent, but Ebbetts Pass is down to 97 percent and Horse Meadow is at 78 percent of average for this time of year. The Walker River basin is at 99 percent of average and the Lake Tahoe basin is at 84 percent.