High pressure will build over the south of the South Island this weekend, driving a very cold southeasterly airflow over Canterbury later on Sunday. Airflow is expected to remain from the east and southeast through Thursday, perhaps into Friday. This airflow will be very cold and damp with persistent low cloud and high humidity. 

 For farmers:

Expect a long period of bitterly cold temperatures accompanied by heavy cloud from later on Sunday through Thursday. Snow accumulations are expected above 300m, likely above 200m, and some falls to below 200m are possible.

 On Sunday evening and night expect a period of snow, with 5-10cm of snow accumulating above 300m, and 3-5cm above 200m. There may be some light accumulations below 200m down to near sea level. From Monday to Wednesday expect frequent light snow showers above 200m, and sleet with occasional snow flurries below 200m. Over the three days a further 5-10cm may accumulate above 300m, a further 1-3cm above 200m, but accumulations below 200m look unlikely. There is a small chance of a heavier fall of snow to low levels on Wednesday, chiefly in North Canterbury.  Snow showers should clear Wednesday night or early Thursday. However, temperatures on Thursday will remain very cold with heavy cloud. 

 Over 4-5 days total accumulations of 10-20cm are likely above 300m. Accumulations above 200m will fluctuate through the period. 

Even with light snow falls, this will (at the very least) be a stressful time for new-born lambs due to the long period of very cold temperatures and dampness. It could become worse than just stressful.

 For travellers:

Snow may affect roads on Banks Peninsula, and the high Plains and hill country, from Sunday evening through at least next Wednesday. Disruption is possible during this time. There may also be some periods of disruption on the alpine passes, especially on Sunday night and on Wednesday.

 Elsewhere

Snow flurries to low levels are likely in Otago on Sunday and Monday.

Snow will affect higher altitudes in Marlborough and also the eastern and central North Island during this time.