Non-stationary atmospheric pathways limit seasonal predictability of Eurasian autumn snow impacts on East Asian winter temperature

Eurasian autumn snow has been widely regarded as a source of East Asian winter predictability, yet its influence is strongly non-stationary. Here we show that this non-stationarity reflects a reorganization of the dynamical pathway rather than a simple loss of snow forcing. Using multiple snow products, ERA5 diagnostics, and ECMWF SEAS5 hindcasts, we identify a spatially organized October Eurasian snow mode that is more closely linked to East Asian winter temperature than basin-mean snow loading. Observations indicate that snow memory partly persists into early winter, whereas the intermediate atmospheric pathway is substantially less stable: tropospheric circulation adjustment weakens, and the snow-WAFz and WAFz-AO10 relationships are weak, seasonally and vertically dependent, and not consistently significant across periods. Despite this variability in the intermediate pathway, the October snow-East Asian winter temperature relationship remains comparatively robust across periods. The final East Asian temperature response is limited by a reorganized downward/regional projection. SEAS5 reproduces the upstream snow predictor reasonably well but fails most clearly at the WAFz-AO10 stage, where none of the ensemble members reproduces the observed sign of the relationship. This contrast identifies dynamical pathway fidelity, rather than snow representation alone, as a key constraint on seasonal predictability.