The Polar Vortex Test: Winter 2026–27, El Niño, the QBO and the Limits of Prediction

Five record-setting September polar-vortex wind days, an October shift below normal and a potentially historic El Niño set the stage for Northern Hemisphere winter 2026–27. Pattern Nexus reconstructs 36 winters of ENSO/QBO/Arctic Oscillation records and 32 seasons of Chicago snowfall, runs rolling out-of-sample regression tests, investigates planetary-wave displacement, solar forcing, sea ice and cold-delivery routes, and issues a cautious initial winter outlook with a late-November revision.