**A strengthening marine layer and enhanced onshore flow from the Pacific are the dominant drivers keeping trader-implied odds centered on 74–77°F for Los Angeles’s August 13 high.** Official National Weather Service guidance shows a cooling trend this week, with widespread low clouds and fog limiting daytime heating and producing forecast highs in the low-to-mid 70s—well below the mid-August climatological average near 84°F. Recent model runs and surface observations confirm the marine layer has deepened, with its inversion trapping cooler air near the coast and suppressing the usual afternoon warming. This setup aligns closely with the market’s heaviest concentration at 76–77°F (49.5%) and 74–75°F (28.0%), while lower probabilities for 78°F+ reflect the low likelihood of the layer eroding quickly enough for significant warming. Traders are also weighing the typical 2–4°F difference between cooler coastal/LAX readings and slightly warmer downtown or valley locations. The next National Weather Service forecast updates and morning sounding data will be the key near-term catalysts that could shift these implied probabilities.