1000 hPa height (solid contours every 3 dam), 1000–500 hPa thickness (dashed contours every 6 dam), and Total RHS of Petterssen Development equation (shaded in x10-9 s-2).
NCEP GFS analyses and forecasts on 1x1 latitude-longitude grid are smoothed with a 9-point local smoother run 30 times.