Winter 2007 – what’s happening with the weather?

Last winter (2006) will long be remembered as a year Canterbury endured one of its biggest snowfalls. Thousands of homes were without power and telephones for weeks, and farms and isolated households struggled to cope as businesses and transportation was affected. It was one of the most severe weather events for thirty years.

Photographs of the storm and it’s aftermath were captured in a commemorative book.

Weather is something everyone’s got an interest in – be it choosing what to wear, or choosing what crops to plant or how to manage stock on a farm – it affects every day in our lives. So what does this year have in store? Are our winters getting colder? We talk to well-known weather personality and MetService Ambassador Bob McDavitt:

Autumn seems to have been warm, yet last winter we had a major snow event - what would you say we were in for this year?

Average temperature in April (2007) for Christchurch was 11.1 degrees - that was 1 degree below normal. And in May so far it’s 11.3 degrees, so its been steady, but the norm for May is nine degrees so its now two degrees ‘above normal’.
Seasonal outlooks are based on looking at trends of sea temperature covering the pacific Ocean, and the coming winter is likely to be a La Nina - caused by cooler than normal seas around the eastern equatorial Pacific.
For New Zealand this usually means that the southwest fronts have less grunt. So winter may be milder and drier than normal.
Last December a lot of cold water flooded out of the polar circle and over NZ, it even had some icebergs… there only two places around the planet that these accumulations of Antarctica melt-water can go north, and NZ is near one of them, and the result was one of the coldest Decembers here in 60 years.

Will the skiers and snowboarders be happy, or will they have to wait for later in the year?

There is likely to be a delayed accumulation to the mountain snow, but its already cold enough for the ski fields to make their own snow.

Are winters becoming warmer with global warming or colder with more severe events such as last year’s snowfall? Or is it warmer on average with more severe cold snaps?

With global warming the southerlies are about a degree warmer now than they were 100 years ago. But they’re always going to be chilling in winter, because the South Pole is always going to be a refrigerator during its six dark months of winter. Cycles in weather and many and many-faceted, so that lots and lots of combinations are possible.
The water that made up last June’s snow came from Indonesian waters. Conditions were just right to turn that water into snow thanks to the serendipitous arrival of a cooling southerly as the jetstream carrying the moist air came by. The southerlies were stronger than normal in Canterbury last year because of a La Nina pattern. We are going through an epoch (20-30 years) where we are likely to have more La Ninas than El Ninos - this is called a Pacific decadal oscillation. We are also at the low point of the sunspot cycle at this stage and that encourages dryness. Next high point, which encourages storms, is 2011 to 2012.)

We often have frosts in the winter. How is the severity of a frost measured?

A grass minimum thermometer is used and every degree below zero is counted as one degree of frost, starting at -1C
slight frosts are -1 to -3
moderate between -3 and -6
severe between -6 and -9
and if it’s more than -9 it's very severe

Is New Zealand weather harder to predict than say, Australia’s?

Weather is a mix of pattern and chaos. There is more chaos in the weather over the southern ocean than there is in the tropics and we are closer to the southern ocean than Australia. Also Australia’s interior is naturally arid, so has less weather. So the answer’s yes.

Several areas in Canterbury claim to have micro-climates - such as Lyttelton Harbour or Horotane Valley - what is a micro-climate, and how "micro" can it be?

A microclimate is an area where its attributes modify the incoming weather in a unique way. Every building, every garden, every tree, every human being is a microclimate.

Are super-computers the best way to predict weather?

For a scientist the way to understand the world is to observe what’s happening, ponder about the processes at work, runs experiments to test things, and then report the findings. This is the scientific method and computers run the mathematical models based on data from the incoming observations.

There are other ways of weather forecasting involving astrology, but for me science is best. Weather is a mix of pattern and chaos, and five minutes after the data is collected for our computer run, someone somewhere lights up a cigarette, or there’s a bush fire or something chaotic that tweaks the weather into a new pattern that hasn’t been taken into account by the computer. So computer models have limitations.
The winning formula is to get the best idea (from MetService) of what’s coming your way from over the horizon, and then TWEAK this using your own observations within your horizon and your own knowledge of your own micro-climate.

What did we use before super-computers?

When I started forecasting we used much the same physics as is done by the computer, but we only had time in one shift to produce one "analysis" then one "prognosis" and then write out the forecasts for tomorrow. With computers we can go days into the future based on extrapolated trends from collected data.

Libraries are a great place for finding out more about weather and the way the earth works - are there any weather related books you can recommend to readers?

The New Zealand Weather Book by Erick Brenstrum.

Winter’s also a great time for recreational reading - do you have a favourite read?

The Listener magazine is my favourite read each week, and I don’t get to read it all before a new one comes.

Weather resources

Our Internet Gateway

• World Meteorological Organisation weather information for Christchurch.
• Ken Ring is a well-known long range forecaster who bases his predictions on the moon. His long range weather web site explains.
• MetService web site shows local and national weather as well as skifields weather reports.
• Think it’s cold here? See what’s happening at Scott Base, Antarctica via their web cam.
• Niwa article on weather prediction and Māori environmental knowledge
• A website for children with weather games, stories hands-on science activities.
• Weather resources – heaps more links!

Resources in our libraries

• Books on New Zealand weather
• Weather information and extreme weather titles