High‐altitude observations of mountain meteorology remain extremely rare in the Southern Alps despite their importance for detecting changes in seasonal snow and glacier extent. To address this, we present a unique in situ analysis of surface meteorology, including radiative forcing from clouds, using automatic weather station data obtained near the terminus of Brewster Glacier in the Southern Alps of New Zealand over the period 2010–2020. The average air temperature is 2.1°C at an altitude of 1,650 m above sea level, and seasonal cycles of surface temperature and albedo indicate the automatic weather station (AWS) site is typically snow‐covered between June and November. Snowfall can occur anytime of the year, but rainfall accounts for more than half of the total precipitation (56%). In the absence of strong gradient airflow, a katabatic wind often develops on the glacier, which is strongest at night time and early morning. Partly cloudy conditions are most frequent (43%) at a daily time scale, followed by overcast (34%) and clear‐sky conditions (23%). A distinct diurnal and seasonal cycle of cloud cover is observed, with clouds most frequent in the afternoon during spring. Daily clear‐sky conditions are most common during winter, in particular in June, while the atmospheric transmission of shortwave radiation is lowest in summer. For 4 months of the year (May–August), the increase in incoming longwave radiation by clouds exceeds the decrease in incoming shortwave radiation. Interannual extremes in melt on Brewster Glacier cannot be fully attributed to summer air temperature anomalies and future work should seek to examine the influence of clouds and atmospheric moisture fluxes on seasonal mass balance variations.

A distributed mass-balance model is used over a 10-year period for the re-analysis of a glaciological mass-balance time series obtained from Brewster Glacier, New Zealand. Mass-balance modelling reveals glaciological mass balance has been overestimated, with an average mass loss of −516 mm w.e. a−1 not captured by observations at the end of the ablation season, which represents 35% of the annual mass balance. While the average length of the accumulation season (199 days) remains longer than the ablation season (166 days), melting is not uncommon in the core part of the accumulation season, with 2–32% of total snowfall being melted. Refreezing of meltwater is also important, with 10% of surface and subsurface melt being refrozen in the present climate. Net radiation, driven primarily by net shortwave radiation, is the main contributor to melt energy, with melt variability mainly influenced by the turbulent heat fluxes, net longwave radiation and the heat flux from precipitation in the ablation season. Snowfalls in summer are an important moderator of melt, highlighting the critical role of the ice-albedo feedback and phase of precipitation on seasonal mass balance. A complete homogenisation of the long-term glaciological mass balance for Brewster Glacier is still required.

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