Reading the vortex
Core: potential vorticity above the inner threshold, coloured by wind speed, bright = 90 m/s and more
Shell: the outer PV threshold, GFS in cyan
IFS in gold: the open ECMWF feed now reaches 10 hPa, about 32 km, so the IFS vortex is cut off there (dashed ring); the GFS goes on to 1 hPa
Chart: analysis (white), GFS run (cyan), GEFS ensemble mean with the 10–90 % band (green, 35-day run), ERA5 1979–2025 mean and range (grey). Below zero the vortex has reversed
isentropes 400–1300 K ≈ 14–45 km · polar cap 20–90° N