This big high is doing two things with temperatures – making for colder nights and then milder afternoons. This pattern continues into the weekend before a sub-tropical flow over Sunday night and into early next week finally warms the nights up.
While cold nights in June are very normal the run of clear skies following a southerly at the start of the week has left overnight temperatures below average for quite a few places – while the days are warming up nicely with plenty of sunshine and lack of wind.
Both Friday and Saturday have average to slightly warmer than average afternoons for late June, while again tonight (and tomorrow night) will be colder than average in most places. Warmer winds then finally develop on either Sunday or Monday in many places and should make for a warmer week next week.
WeatherWatch.co.nz says overnight lows in the north, for example the Waikato plains, are about to jump 15 degrees from -1C tonight to +14 by next week (next week’s overnight match Hamilton’s current daytime highs!). Daytime highs also go up, not by as much but still a noticeable jump from 14s this week to 17s next week.
Overnight lows in Canterbury, as a South Island example, will also jump from -2 recently to +8 by next week, a lift of +10 degrees overnight while daytime highs in Christchurch go from 11 up to 16C for a short time next week.