A simple two-predictor regression model is developed to estimate the relative influence of large-scale low frequency ocean-atmosphere dynamics and high frequency atmospheric forcing on peak sea surface temperature (SST) anomalies associated with El Niño/Southern Oscillation (ENSO) variations for the period 1980–2005. One predictor is equatorial warm water volume (WWV), which is an index for the role that upper ocean heat content plays in regulating ENSO variability. The other predictor characterizes high frequency atmospheric forcing in the western Pacific linked to the Madden-Julian Oscillation (MJO). The two-predictor model accounts for about 60–65% of peak Nino3.4 SST anomaly variance at 2–3 season lead times and suggests about equal influence (on average) of low frequency dynamical processes and the MJO on peak ENSO SST anomalies over the past 25 years. The implications of these results for ENSO prediction are discussed.