14 day weather forecasts

 

The accuracy of weather forecasts is heavily dependent on how well we can define the current state of the atmosphere, because this forms the foundations of any computer weather prediction. The current state of the atmosphere - involving the global distribution of temperature, pressure, wind humidity and other variables, both at the surface and in the upper layers of the atmosphere at a given moment - forms what we call the ‘initial conditions’, which are the starting point for all future predictions.

If we could produce perfect initial conditions, the computer could theoretically produce perfect forecasts. But to do this we would have to know where every molecule of air is at any one moment, and the direction and speed of every molecule’s movement. Clearly this will never be possible, and this imposes an upper limit on how far ahead we can usefully forecast the weather. The errors we begin with in our initial conditions tend to magnify with time, producing a decrease in forecast accuracy the further ahead we try to go.

Interesting work done with numerical weather prediction over the last two decades or so has revealed that the atmosphere adopts different states of predictability over time, and this has been demonstrated by performing multiple computer runs, each with slightly different initial conditions. On some occasions, a small difference in the initial conditions will produce only a slight change in the forecasts, out to, say, four days ahead. At other times, starting with only slightly different initial conditions will produce vastly different forecasts, indicating a state of high unpredictability in the atmosphere at that time.

This extreme sensitivity to initial conditions is one of the classic signatures of a so-called ‘chaotic’ system, in which predictability is always limited, even with near-perfect initial conditions.

The atmosphere also seems to adopt stable and unstable modes - times where the weather patterns are persistent and predictable and others where atmospheric motion is volatile with a high degree of unpredictability.

This leads to the curious mathematical phenomenon called ‘the butterfly effect’ in which it is theoretically possible, in certain ‘knife-edge’ situations, for a butterfly to flap its wings over Melbourne and precipitate a cascade of atmospheric motion that results in a tornado in Kansas or a tropical cyclone near Fiji. However, while this is theoretically possible, it is considered to be an unlikely event in reality.

Taking all these factors into account, meteorologists generally concur that meaningful weather forecasts showing real skill will, over the next fifty years or so be achievable out to about 14 days ahead. After that, the inherent unpredictability of the atmosphere will probably form a ‘glass ceiling’, impenetrable to even the most extensive observational network and the largest computers.

 

7 day weather forecasts

The Weather Channel provides 7 day weather forecasts for capital cities and metropolitan areas, plus get an additional 3 days on top as well as our interactive Weather Map.

Sydney 7 day forecast
Brisbane 7 day forecast
Melbourne 7 day forecast
Canberra 7 day forecast
Adelaide 7 day forecast
Hobart 7 day forecast
Perth 7 day forecast
Darwin 7 day forecast