Short- and-medium term trends in the hydrometeorology of the central Southern Alps are examined with the aim of developing monthly and seasonal inflow forecasting models for alpine hydro lakes. Both ambient air temperature and precipitation are considered principal components in the generation of inflows. These two meteorological variables display both strong annual cycles and longer term fluctuations which are linked to the influence of different synoptic circulation systems and their regional impact, through such mechanisms as the ENSO phenomenon. Recent investigations have indicated that negative phases of ENSO tend to delay the onset of the spring melt season and to result in drought conditions within the central Southern Alps. Such conditions during 1991 and 1992 were compounded by a global increase in atmospheric turbidity following two large volcanic eruptions, and contributed to a national energy crisis in New Zealand during the 1992 winter. Both seasonal and monthly empirically derived inflow models are assessed, incorporating temperature, precipitation and circulation parameters to predict inflows. Although inflows for these time-scales correlate strongly with precipitation, temperature and atmospheric circulation for the same period, predicted inflows one season or month in advance did not. This supports the need for much shorter term monitoring of meteorological conditions within such alpine catchments. In addition, there also appears to be a need for quantifying inflows generated from the present long-term retreat of major eastern alpine glaciers, which also make a significant contribution to lake inflows.