The net longwave radiation at the sea surface (LW↑↓) was measured over the eastern North Pacific Ocean for 22 days during the fall of 1982. These measurements were made from the R/P FLIP as part of the Optical Dynamics Experiment. The mean LW↑↓ emitted from the sea surface was 52.0 W/m2 with a variance of 802.6 W2/m4. The largest fraction of the variance was observed to be in the diurnal frequency band. LW↑↓ and the total cloud amount exhibited significant diurnal cycles (amplitudes of 13.5 W/m2 and 7%, respectively) which were negatively correlated. LW↑↓ measurements were compared with values obtained from seven different bulk formulas for LW↑↓ in order to evaluate their predictive capabilities. These formulas predict less than 45% of LW↑↓ variance, indicating that these methods are inadequate for the description of LW↑↓ variability. Statistical predictions were made using linear hindcastors to examine the relationships between LW↑↓ and other surface meteorological and oceanographic parameters. The signs and magnitudes of the arbitrary coefficients in the linear hindcastors are consistent with hypotheses used for a conceptual model of radiant heat transfer between two parallel gray plates through an interacting medium. The highest predictive skill levels (54.3-55.3% of the variance explained) occur for the case of a two component linear hindcaster where both the cloud layer and the water vapor concentration above sea surface are taken into account. The success of the statistical predictions indicates that the fundamental physics relevant to LW↑↓ variability are incorporated in the conceptual parallel plate model.