The great thing about Christchurch is that it's fairly warm all year. Although the Winters (June to August) can get a lot of rainfall, with a drop in the temperature, it can be dealt with if you have a rain jacket and some warm clothes. Gets tips on how to pack with What To Bring On Your New Zealand Holiday.
RAIN – Rainfall in mm
RAIN – Rainfall in Inches
Summer holidays start in mid-December to late January. There are also two week breaks between school terms, usually in mid-April, mid-July and late September.
The Queen's birthday is celebrated on the first Monday of June while Labor Day is celebrated on the fourth Monday of October. Know the holidays with Public Holidays In New Zealand.
Summer (December to February) is the most popular time to be in Christchurch, although Autumn (March to May) and Spring (September to November) also has the warm days but less tourists. Remember that no matter what season you decide to visit, it is best to make early reservations on your campervan and accommodations. MyDriveHoliday has great Motorhomes For Hire as well as a list of great Holiday Parks In Christchurch.
Source: Google Maps