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Publication Notice

April 26, 2013

A journal article entitled Mesoscale variations of the atmospheric snow-line over the northern Sierra Nevada: Multi-year statistics, case study, and mechanisms by J. Minder and D. Kingsmill, was recently published in the March 2013 issue of the Journal of Atmospheric Science.

Observations from several mountain ranges reveal that the height of the transition from snowfall to rainfall, the snow-line, can intersect the terrain at an elevation hundreds of meters below its elevation in the free air upwind. This lowering of the snowline over several km of horizontal distance affects both the accumulation of mountain snowpack and the generation of storm runoff. A unique multi-year view of this behavior based on data from profiling radars in the northern Sierra Nevada deployed as part of NOAA's Hydrometeorology Testbed is presented. Data from three years of storms show that the lowering of the snow-line is a feature common to nearly all major storms, with an average snow-line drop of 170m.

The behavior of the snow-line is investigated in detail for a major storm over the northern Sierra Nevada. Comparisons of observations from balloon soundings and profiling radars with high-resolution computer simulations using the Weather Research and Forecasting (WRF) model show that WRF is capable of reproducing the observed lowering of the snow-line in a realistic manner. Modeling results suggest that radar profiler networks may substantially underestimate the lowering by failing to resolve horizontal snow-line variations in close proximity to the mountainside. Analysis of model output indicates that air temperature processes related to the atmospheric blocking effect of the terrain, localized cooling due to melting of terrain-enhanced snowfall, and variations in the depth of the melting layer all play important roles. Simulations are surprisingly insensitive to model horizontal resolution but have important sensitivities to model physics.

Minder, J.R. and D.E. Kingsmill, 2013: Mesoscale Variations of the Atmospheric Snow Line over the Northern Sierra Nevada: Multiyear Statistics, Case Study, and Mechanisms. J. Atmos. Sci., 70, 916–938, doi:10.1175/JAS-D-12-0194.1.

Basemap of observing systems Event-based climatology from major storms during three cool seasons
Top: Basemap of observing systems employed in this study. Bottom: Event-based climatology from major storms during three cool seasons (2005/06, 2006/07 and 2007/08).