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Early Arctic Stratospheric Disruption Recast as 'Canadian Warming,' Pointing to Cool, Dry Start for California

UK forecasters describe an unusually early, likely minor SSW whose potential effects there would most likely not appear until mid to late December.

California weather is likely to be cool and dry as December arrives, owing to a high-pressure ridge over Alaska and Canada. 
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Long-range weather models show a jet stream pattern that aligns with what researchers expect following a “Canadian warming” event. A strong ridge of high pressure (red and orange) deflects storms away from California, while a cold and stormy pattern sets up in the east. 
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Overview

  • New analyses indicate the polar vortex did not meet the threshold for a major sudden stratospheric warming, with the disturbance behaving as a wave‑reflection or “Canadian Warming.”
  • The pattern favors a ridge over Alaska and western Canada, raising confidence in a cool, largely dry setup for California in early December and limiting atmospheric rivers.
  • Researchers Judah Cohen and Matthew Barlow say the evolution matches a ridge‑dominant phase that can briefly lock the jet stream, with the Pacific Northwest and northern California most prone to colder conditions.
  • The Met Office calls the signal unusually early and likely minor, emphasizing that any surface impacts typically lag by one to three weeks.
  • UK outlooks retain wide uncertainty for mid‑to‑late December, with plausible outcomes ranging from a colder spell to milder, unsettled weather with wind and rain.