Mesoscale variability in the marine atmospheric boundary layer is particularly pronounced within roughly a Rossby radius of the coastline. Along the U.S. West Coast, mesoscale structure can be greatly influenced by several factors including: orographic forcing, supercritical flow effects, strong SST gradients, cross-coast transition in surface roughness, as well as diurnally driven sea/land breezes and mountain/valley circulations. We examine marine layer mesoscale variability utilizing data from 20 NDBC buoys and a reanalysis of COAMPS (Coupled Ocean/Atmosphere Mesoscale Prediction System) forecast fields. Monthly mean characteristics have been obtained from the re-analysis fields. During the warm season, these data show pronounced spatial variability in layer depth, flow speed and integrated cloud amount as well as in surface fluxes and stresses that are being used to drive the COAMPS ocean model (NCOM). Preliminary results from July 1999 indicate a 1-2 degree cold bias in COAMPS near-surface temperature in conjunction with an over-prediction of low-level moisture. Adjustments to the buoyant forcing in the turbulence parameterization scheme are being evaluated as improvements to correcting these biases. Seasonal changes in the spatial patterns of coastal mesoscale variability are also examined in relation to marine layer criticality (i.e., Froude number). For the summer months, supercritical flow features have been previously established in field experiments such as Coastal Waves 96 and the Coastal Ocean Dynamics Experiment.