Wellington's springtime temperature variability, driven by frequent nor'westerly winds and passing frontal systems, keeps the lowest temperature on September 4 uncertain across 9–13°C in current model runs. Official guidance from sources like the Met Office indicates an overnight minimum near 11°C after daytime showers and strong NW winds ease, allowing clearer skies for radiative cooling. Key differentiators include cloud cover timing, which reduces heat loss if persistent, versus calm conditions post-front that enable greater overnight drops; air mass origin from the Tasman Sea versus cooler southerlies; and local topography amplifying wind mixing or sheltering. Ensemble spreads in global models explain the tight market clustering around 12–13°C, with lower probabilities for extremes reflecting historical September baselines near 9–10°C lows amid ongoing uncertainty in the next 48-hour forecast updates.