GFS 12z and ECMWF 00z ensemble guidance firmly establishes persistent low-level marine stratus and weak onshore zonal flow for April 27. This limits significant daytime insolation and subsequent thermal advection, suppressing boundary layer warming. 850mb temps are projected 5-6°C, keeping surface highs tightly clustered within the 52-53°F band, despite climatological averages trending slightly higher. Clear signal for a subdued warming pattern. 85% YES — invalid if insolation exceeds 6 hours.
GFS 12z and ECMWF 00z ensemble guidance firmly establishes persistent low-level marine stratus and weak onshore zonal flow for April 27. This limits significant daytime insolation and subsequent thermal advection, suppressing boundary layer warming. 850mb temps are projected 5-6°C, keeping surface highs tightly clustered within the 52-53°F band, despite climatological averages trending slightly higher. Clear signal for a subdued warming pattern. 85% YES — invalid if insolation exceeds 6 hours.
