Climatology of Lake-Effect Precipitation in the Lake Tahoe, CA/NV Region

The frequency and environmental conditions favorable for lake-effect precipitation over Lake Tahoe, Pyramid Lake, and Honey Lake in northern California and western Nevada were examined for the 14 winters (September-March) from 1996/97 to 2009/10. Weather Surveillance Radar-1988 Doppler (WSR-88D) data from Reno, Nevada (KRGX) were used to identify 64 lake-effect events. Events occurred as 1) well-defined isolated bands that had an extension downwind (BAND events), 2) an isolated region of convective precipitation that persisted over a lake (OLC events), 3) a BAND or OLC event embedded within a widespread region synoptic precipitation (SYNOP events), or 4) an event that transitioned between two event types (TRANS events). OLC events are a unique morphology not previously observed in lake-effect environments. Seventeen OLC events were documented in this study, with OLC events having occurred on both Pyramid Lake and Lake Tahoe.

An examination of the characteristics of all 64 lake-effect events provides several findings that are useful for comparison with other lake-effect studies. Lake-effect events occurred most frequently in October with an average of 1.4 lake-effect events per year. This peak in event frequency is notably earlier than that observed for lake-effect in other regions. Events had an average duration of 6.2 hours, about half the duration as compared to observed events on Lake Champlain, the New York State Finger Lakes, or the Great Salt Lake. In general, lake-effect events in the Lake Tahoe region 1) had surface air temperatures below freezing, suggesting frozen precipitation, 2) average wind speeds of 2.1 m/s, notably weaker than in other studies, and 3) an average surface lake—air temperature difference of 9.7°C and an average lake—700-hPa temperature difference of 18.5°C. The climatology of lake-effect precipitation events shows some notable differences in lake-effect event characteristics from previous studies of lake-effect in other regions and provides a foundation for the subsequent investigation of the connections between mesoscale processes and regional climate variability.