The market's near-certain positioning on a highest temperature of 61°F or below stems from National Weather Service and NOAA model consensus projecting an unseasonably cold air mass over Denver on May 18, 2026, with daytime highs around 46°F and accumulating snow. This sharp departure from the month's typical 72°F average high arises from a vigorous upper-level low and associated cold front crossing the central Rockies, which has already triggered record-low readings and widespread flurries across the Front Range. Ensemble guidance shows tight clustering well below seasonal norms through the period, with only minor spread in maximum readings. A delayed frontal passage or rapid warm advection could lift temperatures modestly, though current observations and short-range models indicate negligible risk of breaching the 61°F threshold.