Persistent marine layer conditions and steady onshore flow from the cooler Pacific Ocean suppressed daytime heating across coastal Los Angeles on May 15, locking the official high at Los Angeles International Airport into the narrow 68–69 °F range. National Weather Service observations and model consensus confirmed the layer’s persistence through peak heating hours, preventing the typical inland warming that would otherwise push readings several degrees higher under clear skies. With resolution criteria tied directly to the KLAX station reading, traders assigned near-certain implied probability to this band once the day’s data aligned with climatological expectations for a strong May marine layer. Only an unexpected rapid dissipation of the layer or a sharp shift to offshore winds could have altered the outcome, scenarios unsupported by the final observations.