A narrow but powerful trough of low pressure will move over Canterbury on Wednesday night, bringing an interaction between mild, humid air to the north and much colder air from the south.

This will bring a short, sharp spell of wet weather, snowy over higher ground according to Blue Skies Weather & Climate Services Ltd.

For farmers:

Expect snow lowering steadily from late evening Wednesday to reach 200m by early Thursday. Snow will ease to flurries early on Thursday morning, and these will linger till late in the day then clear. Expect accumulations of 10-20cm above 500m, 3-5cm above 300m, and some flurries (but unlikely to become accumulations) possible on the upper Plains and coastal hills above about 200m. Sleet at times below 200m. Strong winds are not expected. At this stage, Friday and next weekend look likely to be fine but cold. 

For travellers:

Snow will likely affect all key alpine passes on Wednesday night with brief heavy falls possible. Expect some travel disruption. 

Elsewhere

Snow to below 200m is also likely in Southland and Otago later on Wednesday, and to 400m in Marlborough early Thursday morning.