Traders solidly favor 56-57°F as Seattle's highest temperature on March 18, mirroring the National Weather Service's latest forecast of 55-57°F under persistent marine layer clouds and light onshore flow typical for Pacific Northwest spring. This positioning draws from verified model ensembles like GFS and ECMWF, which converge on mid-50s highs after recent cool snaps, consistent with Seattle's March climatology averaging 55°F since 1991. Historical data shows rare March spikes above 60°F tied to strong ridging, but current upper-air patterns lack such signals. A realistic challenge would require an abrupt high-pressure build or downslope winds accelerating warming, though probabilities remain under 1% per probabilistic outlooks.