Seattle's August 15 temperature market centers on National Weather Service and ensemble model consensus favoring highs near 78–81°F, driven by persistent onshore marine flow from the Pacific and Puget Sound that moderates afternoon peaks while a warmer-than-average seasonal pattern—marking Seattle’s 14th consecutive hotter summer—lifts the baseline above the 77°F historical average. Key differentiating variables include the strength of the marine layer, which can cap temperatures through low stratus or allow clearer skies for additional warming, alongside subtle shifts in 850 hPa temperatures and wind direction that separate upper-70s from low-80s outcomes. With leading bins closely matched, traders weigh short-term model runs and local observation trends ahead of the daily maximum, recognizing typical forecast uncertainty ranges of several degrees for Pacific Northwest summer days.