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Abstract:
Namibia, a predominantly hot and arid country, rarely experiences snowfall, which is generally restricted to elevated southern regions during winter. On 5 August 2025, light snowfall and sleet were reported near Aus, representing a rare occurrence of wintertime frozen precipitation associated with atmospheric variability in a subtropical dryland environment. This study investigates the synoptic and thermodynamic conditions associated with the event using ERA5 and documentary evidence from media reports and eyewitness accounts, while acknowledging the absence of official meteorological observations at Aus and the limitations in direct snowfall verification. The analysis identifies a short-lived cold-air intrusion, with 850 hPa temperatures approximately 1.5 K (kelvin) below the 1979–2024 winter climatological mean, representing a notable but not extreme cold anomaly rather than an absolute temperature value. Synoptic analysis indicates that the event occurred within a northward-amplified upper-tropospheric trough associated with negative 500 hPa geopotential height anomalies and enhanced cyclonic circulation over southwestern Africa. The interaction between the amplified trough and a subtropical jet stream exceeding 60 m s⁻¹ contributed to a dynamically favourable environment for large-scale ascent. At lower levels, a strengthened meridional pressure gradient and persistent southerly wind anomalies indicate a deep cold-air intrusion extending through much of the troposphere, consistent with transport of cooler air from higher southern latitudes rather than confirmed Antarctic-origin air. Although mid-level humidity anomalies were modest, transient moisture availability combined with dynamically induced ascent and local orographic effects over elevated terrain likely supported the development of frozen precipitation. The results suggest that snowfall in southern Namibia can occur when moderate cold anomalies, limited moisture availability, and organized synoptic-scale circulation patterns coincide, without requiring record-breaking thermodynamic conditions. However, uncertainties remain regarding the relative contributions of moisture transport, terrain-induced effects, and precipitation microphysical processes because of limited observational coverage and the spatial resolution of reanalysis datasets. This case provides a diagnostic assessment of a rare cold-season precipitation event and demonstrates how naturally occurring atmospheric circulation variability can occasionally produce frozen precipitation in climatologically warm and arid environments.
