Current meteorological forecasts for Helsinki on August 17 point to a maximum temperature near 20–21°C, underpinning the tight market-implied odds between those two outcomes. Late-summer climatology shows an average daily high of roughly 20°C, moderated by the Baltic Sea’s thermal inertia and typical high pressure patterns that limit strong advection. Ensemble model guidance indicates modest diurnal warming under variable cloud cover with low precipitation chances, though slight differences in boundary-layer mixing or incoming solar radiation could tip the peak by 1°C. Traders weigh these factors against historical variability, where the exact maximum often hinges on the timing of any afternoon clearing. Updated short-range runs from agencies like the Finnish Meteorological Institute will refine the outlook before resolution.