Intense low creates snow in Australia

First snow of 2000 falls in Australia

South-eastern states record record low temperatures
and electricity use soars sky-high

May 28-31, 2000

Snow fell for the first time in south-eastern Australia this year, while the Australian Bureau of Meteorology said Canberra recorded its lowest daytime temperature on record for the month of May - just four degrees Celsius.

This jet-level chart for May 31 shows the southern ocean between South Africa and New Zealand. You can see an obvious 'kink' in the jet stream (at 30,000 feet or 300hPa) to the south of Australia . Note how this jet actually touches the atmosphere above the Antarctic continent before turning north. Add the combined teamwork of a second jet stream (at 400 hPa) over central Australia and a cloud band over Coral Sea, and you've got stagnation. The west to east migration of weather systems cease for a while, and a blast of icy polar air targets south-eastern Australia.

Elsewhere in NSW, Victoria and the ACT, up to 30 centres also recorded their lowest maximum daytime temperatures for May, resulting in record power consumption as people used to a milder climate kept warm with electric heaters.

Snow forced plenty of road closures. More than 300 people were stranded in their cars after snow closed the Great Western highway leading into Bathurst, NSW. Most of them were rescued and taken to tourist accommodation at the Bathurst Roswell Sheep and Cattle Drome.

In Canberra, local football team the Raiders, played an unusual game against the Sydney Wests Tigers in cold and wet conditions. Squalls at times covered the playing surface in snow and for Wests winger, Tongan-born John Hopoate, it was the first time he'd even seen snow. The thought of playing in it sent a serious chill down his spine!

According to National Rugby League football director Graham Annesley, the match was the first to be played in snow in Australian Rugby League's 92-year history.

How did it happen?

For starters, snow in Australia is not unusual. The Victorian Alps can record overnight falls of more than a metre for several days on end and snowflakes have touched the eucalypt-clad tablelands as far north as southern Queensland.

In this case, however, winter came early to much of the country's south east when a deep high pressure cell to the south of Western Australia squashed tight against an intense 974hPa low pressure cell in the Australian Bight. Together they dragged cold Southern Ocean air northwards. Cold air and moist squalls filling in behind the frontal cloud band brought snow to wide areas of the country's south-east, especially at higher altitudes.

The unusual shape of the high pressure cell said a lot about what was going on at higher altitudes. The jet stream followed a very convoluted course, one arm diving south deep into the southern ocean before turning abruptly north again, another arm traveling east across the centre of Australia. This split jet stream helped to trap systems lying inside the 'loop' of the stream. As a result, the elongated high pressure cell stayed put for several days, maintaining cold and snowy conditions. Forecasters call this a 'blocking high'.

Assisting this stalled high pressure system was a low pressure cell and associated cloud band to the east in the Coral Sea. This massive cloud band was associated with a 'long-wave trough' and together both trough and high helped to keep each other in check, according to Sydney forecaster Ian Robertson.

As well, cold dry and stable air dragged up from the Antarctic on the eastern side of the high pressure cell helped to intensify the high and keep the low stationary.

Charts courtesy of the
Australian Bureau of Meteorology.

The Australian surface wind chart for May 28, shows a deep high pressure cell south of Western Australia and tight isobar lines to the east. These tightly-spaced lines indicate plenty of wind. Because Highs in the southern hemisphere rotate anti-clockwise, and lows rotate the opposite, winds between the two systems are being dragged up from deep in the cold Southern Ocean. The dotted line stretching from the country's south-east towards Cape York indicates a cold front. Winds behind this front brought snow squalls.

Two days later the same high pressure cell has moved only slightly to the east and has intensified. It now directs cold southerly air onto Tasmania, Victoria and NSW, prompting record power consumption as people used to milder conditions keep warm with electric heaters.

This is a good example of a 'blocked' high and this can happen when a kink in the jet stream traps weather systems underneath.