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Winter Snow Level Rise in the Northern Sierra Nevada from 2008 to 2017

Reports that warming temperatures have decreased snowpack in the Sierra Nevada and that the snow line—the elevation where rain changes over to snow—in California's northern Sierra Nevada moved uphill by as much as 236 vertical feet per year between 2008 and 2017
States that the partitioning of precipitation into frozen and liquid components influences snow-derived water resources and flood hazards in mountain environments
Estimates total precipitation falling as snow (snow fraction) between WY 1951 and 2017 using nine daily mid-elevation (1200–2000 m) climate stations and two hourly stations spanning WY 2008–2017
Finds that the climate-station-based snow fraction estimates agreed well with snow-level radar values (R2 = 0.95, p < 0.01), indicating that snow fractions represent a reasonable method to estimate changes in frozen precipitation
Finds that snow fraction significantly (p < 0.001) declined during WY 2008–2017 at a rate of 0.035 (3.5%) per year
Single-point correlations between detrended snow fraction and sea-surface temperatures (SST) suggested that positive SST anomalies along the California coast favor liquid phase precipitation during winter
Reanalysis-derived integrated moisture transported upstream of the northern Sierra Nevada was negatively correlated with snow fraction (R2 = 0.90, p < 0.01), with atmospheric rivers representing the likely circulation mechanism producing low-snow-fraction storms
Identifies a statistically significant positive (negative) trend in winter snow levels (snow fractions) in the northern Sierra Nevada during the winters between WY 2008 and 2017
Finds consistency between increases in the elevation of winter snow levels measured by snow-level sensing radars and estimated snow fractions
Finds that atmospheric rivers are predominantly associated with low- snow-fraction storms, and anomalously warm coastal SSTs appear to favor lower-snow-fraction winters—perhaps by enhancing the upward heat flux during atmospheric river landfalls and promoting zonal flow regimes that increase the advection of warm subtropical air into the northern Sierra Nevada, leading to storms with higher snow levels
This suggests that continued increases in sea-surface temperatures and increased frequencies in atmospheric river landfalls may exacerbate future snowpack decline in the Sierra Nevada

Winter Snow Level Rise in the Northern Sierra Nevada from 2008 to 2017

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