5.6
A lake effect snowfall in western Nevada—part II: radar characteristics and quantitative precipitation estimates
Arlen W. Huggins, DRI, Reno, NV; and D. E. Kingsmill and M. M. Cairns
Lake effect snowfalls are common in the lee of the Great Lakes, and considerable research has been conducted regarding their mechanisms of formation. Less well known, but also relatively common, are lake effect snowfalls in the vicinity of the Great Salt Lake. These events typically occur several times a year and can have a significant impact on commerce and travel in the Salt Lake City metropolitan area. The prediction of these events remains a problem due to their occurrence on the mesoscale, and because quantitative precipitation forecasts by models such as the Eta have generally shown lower skill over the inter-mountain West compared to regions east of the Rocky Mountains. This forecast problem was convincingly brought to light in a dramatic lake effect snow event that occurred in western Nevada in early November 2000.
The Nevada event was unique in both its intensity and duration, and snowfall due to the lake effect generally exceeded snowfall on the western slope of the Sierra Nevada where orographic enhancement generally leads to much greater snow depths. Three different lakes of varying size, Lake Tahoe being the largest, contributed lake effect snowfalls. To the lee of Lake Tahoe, the lake effect snowfall greatly impacted travel along two major highways and within Carson City the capitol of Nevada. Because much of the snowfall occurred in data sparse regions, the NWS WSR-88D near Reno (KRGX) provided much of the real time guidance for forecasters in the Reno NWSFO.
Details of the synoptic evolution and surface observations for this storm are provided in a companion paper submitted by Cairns et al. This paper focuses on the mesoscale characteristics of the radar echo evolution as documented by data from KRGX which were archived throughout the storm. Some features of the event were similar to those documented near the Great Salt Lake, for example wind parallel snowbands. The alignment of the bands was generally along the wind direction in the cloud layer, with the origin being near the center of Pyramid Lake and along the east side of Lake Tahoe. Convective cores reaching at least 7.6 km MSL in height and 45-50 dBZ in intensity were observed over a lengthy period on 10 and 11 November. There also appeared to be some diurnal changes in intensity. The lake effect snowbands were observed to rotate around their origin point as the storm wind directions veered from westerly to northeasterly as a result of the movement of the trough to the east.
Because the WSR-88D was the key real time observation tool in this event, the quantitative precipitation estimates (QPE) were very important to forecasters in the Reno office. The QPEs from the standard WSR-88D Precipitation Processing Subsystem (PPS) will be evaluated and compared to results from a newly developed precipitation algorithm which allows for range corrections based on real time development of vertical profiles of reflectivity. The QPEs of both algorithms are then compared to precipitation observations to the lee of the lakes.
Session 5, Operational Use of Analysis for Forecast Development
Thursday, 2 August 2001, 8:00 AM-10:00 AM
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