Localised bursts of rain a feature of spring

Localised bursts of rain a feature of spring | The Outlook


Weather
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There remains a good chance that spring rainfall overall will be mostly below normal, but brief bursts of rain in small areas could also be a feature.

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LOCALISED heavy rain on parts of the NSW central and Hunter coasts in the past week, while the rest of the state, Queensland and Victoria remained dry is typical of the weather patterns that are favoured during the rest of spring and early summer.

There remains a good chance that spring rainfall overall will be mostly below normal, but brief bursts of rain in small areas could also be a feature.

If any such events occur, they will affect only localised areas - more likely near the coast in NSW and Queensland in late spring but in the early part of spring, one or two such events are possible for Victoria and southern NSW.

The reasons for this prognosis are complicated and a bit speculative at this stage.

First, a neutral pattern in the Pacific often leads to a degree of fluctuation in the upper atmospheric jet stream across Australia.

Such fluctuations can result in convergent bands forming in places and diverging upper air bands in other places.

Diverging upper air can result in lower level air being "sucked up" into the area of reduced pressure in order to balance pressures out.

If this lower air is already a little moist then, as it rises and cools the rainfall potential in the area will increase in the band of uplift.

So, with the sea surface temperatures remaining up on normal off eastern Australia, there is a slightly increased chance of a little moisture being around in the lower levels of the atmosphere - hence the previously mentioned prognosis.

Warmer ocean temperatures around many parts of continental Australia will combine with the expected above normal sunshine over the northern and north-western parts of continental Australia, to support a prognosis of more above average temperatures in spring and early summer.

Australia's 'heat engine' in the north west of the country provides the hot air for most spring heatwaves in eastern Australia and currently, there is little or no cloud in the area, nor is any likely in the coming weeks so the potential is there for bursts of early season hot weather, especially in south east Queensland and north east NSW.

So, as noted previously at this stage, looking right through until the end of summer, rainfall is likely to slightly below but near normal in a few areas - better than in recent years, but still unlikely to be sufficient to overcome the major deficiencies established by the drier years of recent times, especially with the expected above average temperatures developing

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