Reading the record
Thin lines: every autumn since 1948, zonal wind at 60° N and 10 hPa. Below zero the vortex has reversed
Amber: the few autumns that flipped before mid-December, with their date
2026: analysis (white), GFS run (cyan), GEFS members to 35 days (green)
Calendar on the right: one row per winter, the dot marks the first easterly day between 1 November and 31 March. Faint rows before 1958: few observations in the stratosphere then
NCEP/NCAR Reanalysis 1 (PSL) · ERA5T, GFS, GEFS