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ARTICLES >> Environment Weather Watch

Weather Watch - December 2011

Posted by Bestprac on Dec 22 2011

By Susan Carn (Hawker/Blinman Bestprac Group)

I’ve just been to an outdoor wedding south of Adelaide and got caught out by the fickleness of the weather!

I’d been keeping a close eye on the forecast which, up until the day before, was for a fine 23ºC day, so I packed accordingly. To my dismay, not to mention the bridal party’s, the morning forecast had changed to 19ºC with strong winds and possible showers. So why can a forecast change so much and so quickly?

As I understand it, the Bureau of Meteorology receives vast amounts of information from a number of sources. These include observations from all of their weather stations and from weather balloons, which provide information on conditions in the upper air, such as pressure, temperature and humidity. Over the oceans the data needed comes from weather satellites. Supercomputers, making millions of calculations a second, automatically plot all of this data onto charts and also generate forecast maps. Forecasters decide on the most probable outcome and release it to the media. So new information could be received after this, hence a change.

Looking longer term, I’ve found that seasonal climate forecasts are reasonably reliable, probably because they are broad and not looking at specific days. The key is to look at several and get a consensus. This is how I used them in our cropping decisions back in May; The predictions for June and July were for dryer than average rainfall. August, September and October were for average to slightly above average.

When deciding to sow and how much, seasonal forecasts are just one tool in my decision making tool box. There are always other things to consider such as fuel, fertilizer and commodity prices and the state of our soils. This year we had good sub-soil moisture due to La Nina bringing good summer rain.

So with the consensus of seasonal forecasts being an “average at best” outlook for us and weighing up everything else, we decided to sow conservatively again. When I plotted a hypothetical decile chart, using the seasonal forecast outlooks, it tracked at decile 2 to 3. Not good, but we had reaped a moderate crop in a situation like that before, so we thought it might just be ok.

As it turned out we did indeed track along at around decile 2. Early August was particularly nerve racking with a few days of, potentially damaging, hot north winds. (This weather event was forecast a few days before but, of-course, it was not foreseen in a seasonal climate forecast.) We got a reprieve when it was followed with welcome rain, only to be thwarted again by a dry September.

We are nearly finished reaping and the upshot is this:

June and July were dryer than average. So that prediction was correct.
August was around average. Correct’ish!
September was below average. Wrong.
October was average. Correct.
We finished up at decile 2 as predicted. As expected our yields are nowhere near as good as last year, but the wheat is high in protein, so the price should make up for some of the shortfall.

There are different forecast timelines with varying accuracy:

  1. 3 month seasonal climate forecasts can be used to give you a rough idea of what to expect and help you to plan.
  2. Multi-week weather predictions are for 2 to 8 weeks ahead and there are several projects underway to further improve their skill and reliability in the coming years.
  3. Short term weather forecasts can mostly be relied upon, but if you are going away remember to pack for a possible change! (By the way, although cold, it was still a beautiful wedding!)

For a last minute Christmas gift consider the BOM calendar: Great photos and cloud explanations. Get a preview at http://www.bom.gov.au/calendar/photos

Merry Christmas!
 

Last changed: Feb 09 2012

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