High-confidence short-range ensemble guidance (SREG) indicates a significant thermal dip, driven by an optimal radiational cooling setup. GECMWF and GFS deterministic runs, supported by the EC ensemble mean, project a transient 500mb geopotential height trough translating across the Korean Peninsula, promoting continental airmass advection on May 4th. A strengthening 1028 hPa surface high-pressure ridge establishes overnight into May 5th, guaranteeing minimal cloud fraction (< 0.1) and near-calm boundary layer winds (< 2 m/s). This complete decoupling fosters maximal longwave radiation loss. Observed 850mb temperatures are forecasted at +2°C to +3°C, but favorable dewpoint depressions (8-10°C) and the strong nocturnal inversion will drive surface temperatures well below this. Final NCEP HRRR output suggests a Seoul low of 10-12°C. This is a clear underperformance of the 13°C threshold. 90% YES — invalid if cloud cover exceeds 0.5.
High-confidence short-range ensemble guidance (SREG) indicates a significant thermal dip, driven by an optimal radiational cooling setup. GECMWF and GFS deterministic runs, supported by the EC ensemble mean, project a transient 500mb geopotential height trough translating across the Korean Peninsula, promoting continental airmass advection on May 4th. A strengthening 1028 hPa surface high-pressure ridge establishes overnight into May 5th, guaranteeing minimal cloud fraction (< 0.1) and near-calm boundary layer winds (< 2 m/s). This complete decoupling fosters maximal longwave radiation loss. Observed 850mb temperatures are forecasted at +2°C to +3°C, but favorable dewpoint depressions (8-10°C) and the strong nocturnal inversion will drive surface temperatures well below this. Final NCEP HRRR output suggests a Seoul low of 10-12°C. This is a clear underperformance of the 13°C threshold. 90% YES — invalid if cloud cover exceeds 0.5.
