Coupling index (shaded in K), 850 hPa nondivergent wind (standard barbs in knots), and 850 hPa potential temperature (contours every 3oC). The 850 hPa potential temperature is smoothed with a 9-point local smoother run 5 times. The coupling index is computed as the difference between DT potential temperature and 850 hPa equivalent potential temperature.
These plots are derived from the NCEP GFS analyses and forecasts on a 0.25x0.25o latitude-longitude grid.