Forecast models from the National Weather Service and major ensembles show high uncertainty in overnight radiative cooling for New York City on September 21, producing tight market clustering around 60–63°F minimums that together exceed 60% implied probability. Key differentiators include variable cloud cover and low-level wind speeds that modulate heat loss, with clearer skies and lighter winds favoring the lower 60–61°F bin while increased moisture or mixing supports 62–63°F. September climatology places typical minima near 62°F, but recent model runs reflect subtle shifts in a weak frontal boundary and urban heat island effects that keep outcomes within a narrow range. New guidance expected from the evening forecast cycle could resolve some spread before market resolution.