Abstract National Meteorological Center (NMC) data from midlatitudes for three Januaries is used to calculate time series of the zonal mean meridional eddy heat flux and the zonal mean baroclinic stability, as measured by the difference between the zonal wind shear and the critical value of the shear in two-level models. Time- lagged correlations between the two series show a highly significant negative correlation for short time lags, peaking at about −0.4 when the stability parameter lags one half day behind the eddy flux. They also show that strongly unstable conditions are not followed by significant increases in the eddy flux. These results indicate that the synoptic variations of the zonal mean eddy flux are not closely related to the degree of baroclinic instability of the zonal mean flow. The autocorrelation of the eddy flux is compared with those expected for auto-regressive processes. A Bayesian information criterion indicates that the behavior is represented best by a damped oscillation, with a...