31 December 2025 & 1-9 January 2026 Europe, Russia, West Siberian, Caucasus Strong Winter Storm

Synoptic and Strategic Assessment of the 2025-2026 Winter Transition: The Great Eurasian Weather Divergence and Multi-Regional Cryospheric Risk The atmospheric transition encompassing December 31, 2025, and the first nine days of January 2026 represents a critical juncture in the 2025–2026 European and Asian winter season. This period is characterized by what is increasingly termed the "Great Eurasian Weather Divergence," a structural fracture in the hemispheric circulation where two violently competing weather regimes have established dominance across the continent. The synoptic environment is defined by a catastrophic failure of the stratospheric polar vortex, high-amplitude blocking patterns, and the modulating influence of a weak La Niña event in the tropical Pacific. The following report provides an exhaustive analysis of the meteorological drivers, regional hazard profiles, and infrastructure vulnerabilities associated with this volatile window. Stratospheric Parameter (10mb) Late December 2025 State Early January 2026 Projection Zonal Wind Speed Negative (Easterly) Gradual Recovery (Westerly) Core Temperature Strongly Positive (Warm) Cooling / Normalizing Vortex Structure Bifurcated / Displaced Consolidating Tropospheric Coupling High (Active) Sustained Influence Hemispheric Drivers and Stratospheric Mechanics The primary catalyst for the extreme conditions observed in late December 2025 and early January 2026 is an unprecedented stratospheric disruption. Commencing in late November, a Major Sudden Stratospheric Warming (SSW) event triggered a total wind reversal at the 10mb level (approximately 30 kilometers altitude). This phenomenon represents a fundamental mechanical failure of the polar night jet, which typically serves to contain the coldest Arctic air within the high latitudes. The Dynamics of Polar Vortex Bifurcation The SSW event established a massive high-pressure anomaly, or "anti-vortex," in the mid-stratosphere. This feature compressed and deformed the Polar Vortex until its structural integrity failed, resulting in a split into two distinct cores. This bifurcation allows for a massive discharge of polar air masses into the mid-latitudes of North America, Europe, and Asia. The vertical coupling between the stratosphere and the troposphere ensures that these changes manifest as extreme surface weather with a delay of approximately two to three weeks, placing the peak surface impact precisely between December 27, 2025, and January 4, 2026. The strength of the stratospheric winds around the Polar Vortex is typically measured at the 10mb level. Analysis indicates a recovery phase beginning in early January 2026, where the vortex enters a stronger, more circular phase. However, the initial split remains the dominant driver of the surface weather pattern during the January 1–9 window, as the lower tropospheric "legs" of the vortex remain displaced over the continents.