How Does Snow Cover in Eurasia During Fall Impact the US During Winter? The "dipole in Eurasian Autumnal SCE" refers to a well-documented west-east contrast in snow cover extent (SCE) across Eurasia during late autumn, particularly in November. This pattern typically features negative SCE anomalies (less snow) over western Eurasia (e.g., eastern Europe) and positive SCE anomalies (more snow) over eastern Eurasia (e.g., Siberia). This dipole is a key predictor for Northern Hemisphere winter climate variability, as identified in multiple climate studies using reanalysis data and models. Mechanism of Impact on US Winter Weather The dipole influences the US winter through a chain of atmospheric teleconnections, primarily via the stratosphere-troposphere coupling and modulation of large-scale circulation patterns like the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). Here's a step-by-step breakdown of the process: Initial Surface Cooling and Energy Fluxes: The dipole pattern enhances cooling over eastern Eurasia due to increased snow insulation and albedo effects, which reflect more sunlight and lower surface temperatures. This creates a strong temperature gradient, promoting high-pressure anomalies (blocking) over the Ural Mountains. Reduced Barents-Kara Sea ice (often co-occurring with the dipole) further amplifies ocean-to-atmosphere heat fluxes, reinforcing the Ural blocking. Stratospheric Response: The Ural blocking generates upward-propagating planetary waves that weaken the stratospheric polar vortex starting in November–December. This leads to stratospheric warming and a slowdown of the vortex, which persists into winter. Tropospheric Teleconnection: The weakened vortex projects downward, inducing a negative phase of the winter NAO/AO. In this phase: The jet stream shifts southward and becomes wavier. A deepened trough forms over the North Atlantic, allowing cold Arctic air to spill southward. Link to US Winter Conditions: The negative NAO/AO pattern often results in a positive Pacific-North American (PNA) teleconnection, amplifying a dipole-like circulation over North America: a ridge over the western US (warmer/drier conditions) and a trough over the central-eastern US (colder, stormier conditions). This increases the likelihood of: Colder temperatures in the eastern and central US. Increased storminess and snowfall in the Midwest and Northeast. Warmer, drier conditions in the western US (e.g., exacerbating droughts). The signal is strongest in December–January (DJF) and has been observed to strengthen during periods of Arctic warming. This relationship is non-stationary and strongest in recent decades (post-1980s), partly due to Arctic amplification, but it holds across longer records (back to the 19th century) when adjusted for observations. Climate models (e.g., CMIP5) reproduce this link, confirming causality through perturbed snow experiments. Evidence and Predictability Observational studies (1979–present) show the November dipole explains up to 30% of winter NAO variance, with direct ties to US cold spells (e.g., 2013–14 winter extremes). The link is causal, as confirmed in ensemble hindcasts where perturbing autumn snow alone reproduces the NAO response. For the 2025–26 US winter (current date: Sep 20, 2025), monitoring November SCE could refine forecasts, especially with emerging La Niña conditions potentially amplifying cold risks. This teleconnection highlights snow's role as a "memory" of autumn conditions influencing distant winters, with implications for seasonal forecasting. ~Meteorologist Mark Margavage #Winter #Snow #winteriscoming #wxtwitter #wxX