"Boreal winter" refers to the winter season in the northern hemisphere, specifically in the areas closest to the North Pole. It is characterized by cold temperatures, shorter daylight hours, and often snowy or icy conditions. Full definition
Deser, C., A.S. Phillips, and J.W. Hurrell, 2004: Pacific interdecadal climate variability: Linkages between the tropics and North Pacific during boreal winter since 1900. (ipcc.ch)
Arctic sea - ice cover will diminish rapidly under global warming, but its rate of retreat in boreal winter shows large intermodel differences across the models involved in Phase 5 of the Coupled Model Intercomparison Project... (phys.org)
Environmental Research Letters «Arctic warming, increasing snow cover and widespread boreal winter cooling» (ecoshock.org)