**Persistent marine layer influence and onshore flow are keeping San Francisco's June 28 high tightly clustered in the upper 60s to low 70s.** Official forecasts and recent model guidance indicate a deepened marine layer (around 2,000–2,500 ft) with patchy fog and drizzle potential, limiting afternoon warming under typical June "gloom" conditions. This setup favors a maximum near 68–71°F at downtown or airport stations, consistent with the market's two leading bins (22.5% and 21.5%). Differentiation among the close outcomes hinges on small variations in marine-layer depth, wind direction, and fog clearance timing: stronger or more persistent onshore flow and later burn-off cap highs near 68–69°F, while modest compression or brief clearing allows brief warming into the low 70s. No strong upper-level ridge or offshore flow is expected to push temperatures significantly higher, keeping 74°F+ outcomes at lower implied probability. Historical June averages near 67°F and current coastal water temperatures reinforce the cool bias. Traders are weighting the latest National Weather Service and ensemble guidance, which show limited day-to-day spread for this specific date.