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Early and late extremes in the timing of snowmelt have recently been observed in the Pacific Arctic. Subseasonal-to-seasonal forecasts of this timing are important for industry, environmental management, and Arctic communities. In northern Alaska, the timing is influenced by the advection of marine air from the north Pacific by the Aleutian Low, modulated by high pressure centered in the Beaufort Sea. A new climate index that integrates their interaction could advance melt predictions. We define this index based on 850-hPa geopotential height at four fixed locations and refer to it as the Aleutian Low-Beaufort Sea Anticyclone (ALBSA). During positive ALBSA in May, advection of +0.5-1.5 K/day is observed through the Bering Strait. ALBSA is correlated with both snowmelt in northern Alaska and the onset of sea ice melt over the adjacent seas. ALBSA therefore may be suitable for monitoring the relevant circulation patterns and for developing predictive tools.

Plain Language Summary Early and late extremes in the timing of snowmelt have recently been observed in northern Alaska. Forecasts of this timing with lead times of weeks to months are important for area stakeholders including industry, environmental managers, and Arctic communities. We find that transport of air masses from the north Pacific influences the timing of melt in the region. We introduce a new index called the Aleutian Low-Beaufort Sea Anticyclone (ALBSA). When ALBSA is positive, warm Pacific air is observed over the Bering Strait and in the far western Arctic seas. ALBSA is correlated with the timing of spring melt and therefore may be suitable for both monitoring and prediction.