Solving science of weather

The inexact science of weather forecasting is one of modern-day farming's biggest frustrations.

The reality is, for many, planting on the first sign of ants in the kitchen or an aching big toe has paid off as often as taking notice of forecasts.

However, the ability to effectively use weather forecasting as a risk management tool is invaluable to those on the land, according to weather experts, agronomists and experienced producers.

The areas most go wrong are not taking into account the limitations of the forecast methodology they are using, not differentiating between long and short-term forecasts and making decisions based on information from just one source, they say.

Speaking at the 2014 Australian Cotton Conference on the Gold Coast, Queensland, this month, technical specialist with Cotton Info, Jon Welsh, Narrabri, encouraged critical thinking of seasonal climate risk analysis and how it translated into running a farm business.

"Climate risk is critical in farm business management to mobilise resources for output in the good years and exercise cost control in the bad years," he said.

"Dad always said the best sign of rain is when it's running down the gutters.

"But whether you rely on ants in the kitchen or are addicted to models - and there are 23 experimental and operational weather prediction models around the world - you would have been burnt by a forecast at some point."

His advice: source widely, retain perspective and then play what is in front of you.

"Just relying on one source, or two like sources, can be dangerous. You need to survey all the information you can access and at the same time, be aware of the limitations of the information you are sourcing," Mr Welsh said.

Don White, director of Weatherwatch, Australia's longest established independent weather consultancy business, said knowing the difference between, and how to read, both short-term and seasonal forecasts was vital.

"Short-term forecasts are day to day. They are based on models of the atmosphere at a particular time - high and low pressure systems," he said.

"Climatic forecasting looks at general seasonal trends and how the atmosphere is likely to behave in the coming one to six months and are based on sea surface temperatures and analogue years.

"If a short-term forecast says there is a 60 per cent chance of rain in an area, say for example Sydney, tomorrow, that means 60pc of Sydney will receive rain.

"If the seasonal forecast says there is 60pc chance a district will get 50mm in October, that means there is a 40pc chance that district won't get 50mm. They may get 55mm or 40, 20, 30mm or nothing at all.

"That adds up to quite a big chance of not getting much rain at all."

Meteorological consultant Dick Whitaker, WeatherSmart, whose career started with the Bureau of Meteorology in the early 1970s, said early methods of long-range forecasting used sunspots and planetary cycles but sea surface temperatures became the basis for the science in more recent times and the concepts of La Niña and El Niño evolved.

La Niña is formed when there is warm water over the tropical western Pacific and leads to increased rainfall across eastern Australia. It occurs every five to nine years.

El Niño is when warm water is over the tropical Eastern Pacific and leads to decreased rainfall across Eastern Australia.

It typically occurs every three to eight years, develops during autumn, strengthens during winter and spring and decays during summer.

Sea surface temperatures must remain 0.5 degrees Celsius or more above normal for three consecutive months and the Southern Oscillation Index must remain at or below minus 8 for a similar period for an official El Niño.

There have been 26 events classified as El Niño during the past 100 years and 17 resulted in drought, Mr Whitaker said.