Weather blog
Judah Cohen's Arctic Oscillation & polar vortex blog
Regular analysis of the Arctic Oscillation, the stratospheric polar vortex and what it means for Northern Hemisphere winter, written by Dr. Judah Cohen at AER. Everything here links straight through to his own pages.
The author
Dr. Judah Cohen
Director of Seasonal Forecasting, Atmospheric and Environmental Research (AER)
Dr. Judah Cohen leads seasonal forecasting at AER, where his research centres on how autumn snow cover across Siberia and shrinking Arctic sea ice nudge the polar vortex. His 2007 six-step model traces that chain: rapid October snow advance, a strengthening Siberian high, extra wave energy rising into the stratosphere, a weakened vortex or sudden stratospheric warming, and, weeks later, a downward shift that can bring cold outbreaks to East Asia, Europe and the eastern United States.
He also holds a visiting position at MIT's Parsons Laboratory, and his winter outlook has been covered by MIT News and The Washington Post.
Background drawn from his own site and the blog's header. His posts, figures and forecasts are his work, published by AER; this page links to them rather than reproducing them.
Why this matters here
The Arctic Oscillation and polar vortex phases Cohen tracks are plotted on this site's Patterns page, next to how Twin Cities winters have actually behaved in each phase. His work is the seasonal-scale counterpart to the local record: it describes the odds weeks ahead, never a specific day's weather, which comes from the National Weather Service forecast.
See the AO, NAO and ENSO contextLatest update
November 2, 2026
Each update works through the current state of the Arctic Oscillation and the polar vortex, the two-week outlook, and the boundary conditions behind it, from Siberian snow cover and Arctic sea ice to ENSO and the MJO.
The charts, maps and model output for each post stay on his site. Follow the post to see them at full size.
68 dated write-ups on his site, newest first.
Recent write-ups
Every update is also published as a dated PDF.
- Nov 2, 2026Open PDF
- Oct 26, 2026Open PDF
- Oct 13, 2026Open PDF
- Sep 28, 2026Open PDF
- Sep 14, 2026Open PDF
- Aug 31, 2026Open PDF
- Aug 17, 2026Open PDF
- Aug 5, 2026Open PDF
- Jul 15, 2026Open PDF
- Jun 25, 2026Open PDF
- Jun 8, 2026Open PDF
- May 26, 2026Open PDF
External links open on published.aer.com and judahcohen.org. Posts, figures and forecasts are the work of Dr. Judah Cohen and AER; nothing is reproduced here.