Latest ensemble forecasts from the Finnish Meteorological Institute and ECMWF models indicate a mild spring day in Helsinki on May 17, with daytime maxima likely peaking between 15°C and 17°C under partly cloudy skies and light southerly winds. Moderate advection of warmer Atlantic air masses combined with increasing solar insolation supports this narrow range, while subtle model spread on afternoon cloud timing and boundary-layer mixing creates the tight contest between 16°C and 17°C outcomes. Historical May climatology at Helsinki-Vantaa shows average highs near 15°C, so current guidance sits slightly above baseline. Traders are weighting the latest model runs heavily, with resolution hinging on official hourly observations through the afternoon peak.