Aggregating 00z ECMWF and 12z GFS deterministic runs alongside the GEFS ensemble mean, the operational high for KORD on April 28th is consistently modeled below the 54-55°F threshold. The ECMWF projects a 53.5°F peak, while the GFS holds at 53°F. The GEFS 50-member mean is a tighter 52.8°F, with only 15% of members clipping 54°F or higher. A persistent weak 500mb trough over the Upper Midwest precludes significant ridge amplification and robust southerly advective warming. Anticipate light WNW surface flow transitioning to ENE by afternoon, injecting a lake breeze potential that will cap boundary layer mixing and diurnal heating. Surface thermal gradient analysis indicates moderate low-level stability. Sentiment: Local mesoscale discussions flag conditions as 'seasonally mild, not warm.' 90% NO — invalid if 850mb temps exceed +6°C by 18z.
Aggregating 00z ECMWF and 12z GFS deterministic runs alongside the GEFS ensemble mean, the operational high for KORD on April 28th is consistently modeled below the 54-55°F threshold. The ECMWF projects a 53.5°F peak, while the GFS holds at 53°F. The GEFS 50-member mean is a tighter 52.8°F, with only 15% of members clipping 54°F or higher. A persistent weak 500mb trough over the Upper Midwest precludes significant ridge amplification and robust southerly advective warming. Anticipate light WNW surface flow transitioning to ENE by afternoon, injecting a lake breeze potential that will cap boundary layer mixing and diurnal heating. Surface thermal gradient analysis indicates moderate low-level stability. Sentiment: Local mesoscale discussions flag conditions as 'seasonally mild, not warm.' 90% NO — invalid if 850mb temps exceed +6°C by 18z.
