National Weather Service and private model consensus currently favors a high temperature in the upper 70s to low 80s Fahrenheit for Seattle on August 17, consistent with the market's tight clustering around the 78–81°F bins. Persistent marine air influence from the Pacific, combined with light onshore flow and variable afternoon cloud cover, typically caps daytime maxima near climatological August averages of 75–79°F at Sea-Tac. Subtle differences among ensemble runs—primarily tied to the timing and depth of any marine layer intrusion or weak shortwave passage—account for the spread across adjacent 2°F intervals. Updated NWS forecasts and high-resolution model guidance issued overnight will provide the next clear signal on whether conditions trend toward the warmer or cooler side of the distribution.