Isentropic potential vorticity on the 315 (gray contours at 2 and 3 PVU), 330 (shaded in PVU), and 345 (black contours at 2 and 3 PVU) K surfaces. PV on the 315 and 345 K surfaces is smoothed with a 9-point local smoother run 5 times.
These plots are derived from the NCEP GFS analyses and forecasts on a 0.25x0.25o latitude-longitude grid.