Caption: +1000 hPa geopotential height (solid contours every 3 dam). +1000-500 hPa thickness (dashed contours every 6 dam). +1000 hPa geostrophic relative vorticity [shaded according to the colorbar (10-5 s-1)]. +Image was generated from 1.0x1.0o NCEP-GFS data smoothed by 20 passes of a 9-point local smoother.