Recent long-range ensemble forecasts from European and global models show substantial spread for Paris overnight lows on May 21, with central guidance near 10–12 °C but tails extending below 7 °C and above 17 °C, directly supporting the market’s near-even split between the 7 °C-or-below and 17 °C-or-higher brackets. This uncertainty arises from evolving steering patterns over the North Atlantic, where the position of a mid-level ridge versus incoming Atlantic troughs will determine radiative cooling rates under clear skies versus enhanced mixing and warm advection under cloud cover. Historical May climatology places typical minimums around 10 °C, so current model disagreement reflects both normal springtime variability and the limited skill of deterministic runs beyond five days. Updated high-resolution guidance from Météo-France and ECMWF over the next 48–72 hours should narrow the distribution and shift trader sentiment accordingly.