A mild winter of two halves

This year's winter was milder than usual and, along with above average rainfall, was the warmest since 1909.

The winter of 2013 could very well be described as a winter of two halves. The first half saw numerous active troughs along with very cold air and snow. By comparison, the second half felt like spring at times in many places with some very mild air in place along with long fine/dry days and limited cold air and snow.

The powerful storm of late June was perhaps the most intense of the winter, leaving a lasting memory for many of us. Strong to severe gales ripped their way up the country, along with heavy, persistent rain, while up to three metres of snow fell in the South Island high country.

Many factors can influence the day-to-day make-up of the weather patterns over a season but, for most of the winter, the main seasonal influences ENSO, remained in the neutral position.

The biggest thing of note, that brought the weather we experienced during winter, was the source region of the weather systems. The source region of a weather system can play a big part in how cold, warm, wet or even dry a particular weather system is.

The first half of winter had a good mix of weather systems from different directions (northwest Tasman Sea, Southern Ocean and Pacific Ocean to the east). The second half of winter saw no cold southerly outbreaks, except for the final days of August. For the remainder of that period, northerly or westerly winds featured. These are not cold directions. The net result was a winter that was milder than normal, with above average rainfall.

According to NIWA, it was the warmest winter on record since 1909 with the nationwide mean temperature 1.2°C above the winter average.

What is to come?The continued neutral ENSO signal from the Pacific Ocean will keep an element of variety in weather patterns over the next few weeks. Local factors will still play their part in the make-up of our daily weather patterns.

The slightly warmer seas around New Zealand, along with a projected signal for lower pressure in the Tasman Sea, will keep Tasman lows a main feature during the next few weeks. These lows can mix moisture-laden winds from the subtropics with cooling winds from the south, sometimes resulting in several days of strong winds and heavy rain. The point of origin in the Tasman Sea also plays a part in how much moisture these features bring.

There may also be some higher surface pressure anomalies to the south of New Zealand over the next few weeks. As a result, the typical spring pattern of disturbed westerly winds covering the whole country may be slightly metered compared to a typical spring. We can still expect them to bring a procession of cold fronts, usually with more active fronts crossing New Zealand at five- to seven-day intervals, but other weather patterns may be interspersed periodically, especially as we get further into October.

Visiting anticyclones that build in from the west or northwest can still be expected to bring mostly fine days, but cool and perhaps frosty nights.

We are still vulnerable to cold southerly blasts, especially when lows deepen off to the southeast of New Zealand. These potentially offer some late season snow, but will be troublesome during lambing. It could be prolonged if any blocking takes place.

Rainfall over coming weeks should remain just above normal across most of the northwest of the North Island and the north of the South Island. Elsewhere, rainfall will be close to normal or perhaps just below normal.

Temperatures over the next few weeks will generally stay normal for most.