Traders assign closely matched probabilities across the 74–79°F bins for Seattle’s July 23 high because ensemble guidance shows modest spread in marine-layer depth and onshore flow strength from the Pacific. National Weather Service model runs indicate a typical late-July pattern dominated by the subtropical high, with afternoon temperatures moderated near the 76°F climatological average by cool marine air and possible afternoon cloud buildup. Small differences in wind direction or timing of any thermal trough passage could shift the peak by 1–3°F, keeping the distribution tight while lowering odds for values outside the 72–81°F window.