The persistent escalation of nocturnal cooling requirements necessitates passive heat rejection mechanisms that exploit the atmospheric transparency window. This study presents a reduced-order computational model to quantify the nocturnal thermal extraction of a horizontally oriented, water-filled radiative panel under clear-sky conditions. Numerical simulations, performed using Python 3.x, track the sensible cooling trajectory over a 10-hour nocturnal cycle. The model assumes a constant surface emissivity of 0.94 and low wind speeds (convective coefficient 2.5 W·m-2·K-1). Results demonstrate that effective thermal extraction peaks at 71.5 W·m-2 during the intermediate nocturnal interval, yielding a cumulative water temperature reduction of 6.8°C (from an initial 25.0°C to 17.5°C) and an estimated cooling capacity of 0.6 kWh·m-2 per night. The principal novelty lies in the dynamic nonlinear coupling of continuous meteorological fluctuations with the thermal inertia of the circulating fluid, bridging the gap between steady-state nodal models and complex CFD simulations. The quantitative analysis confirms that deep-space radiative exchange is a highly viable supplementary architecture for low-grade thermal management in temperate climates.