It is well known that local variations in frostiness are considerable, even within quite small areas. On a calm, clear night the cold air in contact with sloping ground gravitates slowly downhill to collect in valleys and depressions, and it is these “Katabatic” drifts which are mainly responsible for local temperature variations at night. Gently sloping ground with a northerly aspect tends to be least affected by frost. Favourable sites in coastal areas of Northland are free of frost, although further inland light frosts occur frequently in the winter months. At Albert Park, Auckland, the screen minimum thermometer (4 ft. above the ground) has registered below 32° F only once in nearly 50 years, yet across the harbour at Whenuapai Aerodrome there are eight screen frosts per annum on the average. In the South Island screen frosts occur on most clear nights from May to September. Excluding the uninhabited mountainous areas, the most severe winter conditions are experienced in Central Otago, on the Mackenzie Plains of inland Canterbury, and on the central plateau of the North Island. Even in these areas night temperatures as low as 10° are rarely recorded. Elsewhere over the North Island the winters are mild and pastures maintain continuous growth. In both Islands sheep and cattle remain in the open all the year round.