Active cold front brings dust, storms and heavy rain to SA, NSW, VIC, TAS

The synoptic chart for 5pm EDST today. A low has formed on the front over Melbourne while strong warm northerlies cover eastern NSW and VIC. BoM

A strong cold front moved across SA, TAS and western VIC today, producing widespread duststorms and thunderstorms in hot northwesterlies ahead of it, and dropping temperatures 10 to 12 degrees across the south of the country. A complex frontal zone, with a marked trough leading the colder air by about 300km, crossed the SA coast near Adelaide around 6am. By mid morning, a low had developed in the frontal zone over western Victoria. The slowly deepening low passed over Melbourne late afternoon, and was in central Bass Strait by midnight with a central pressure of 997hPa.

A deep, sharp upper trough accompanied the front, with a 120km/h NNW jetstream ahead and a 16° temperature difference across it at 850hPa (about 1.4km).

Duststorms. Strong convection assisted by the upper jet raised dust to high altitudes ahead of the front, while classic "wall-of-dust" duststorms were common in SE SA, western VIC, southern NSW and also SW QLD. It was described by a Bureau of Meteorology spokesman as the most significant dust event in Victoria in 20 years. The worst duststorms were in the SA and VIC Mallee areas and the VIC Wimmera where visibility was reduced to less than 100m during the afternoon by blowing dust. Squally winds gusted to 80km/h over the whole area, with a peak gust of 96km/h recorded at Naracoorte SA at 3pm.

A duststorm arrived in Mildura around 11am, reducing official visibility measurements at the airport to 800m at midday, 400m at 3pm and 200m at 6pm. Weather station observer Tony Grasso told ABC News that the dust storm turned the sky red and created some of the worst conditions for visibility ever recorded at the station. Conditions were at their worst around 1pm when a squally wind change reduced visibility in the city to around 10m according to press reports, and 20m at the airport. Said one resident: "Visibility went down to 20 metres; it went like night here in Mildura. The front had a wind stop in it so as the dust wall went over it went hushed and you could look up and see the dust blow over. Then it started blowing again." Another resident said "We all expect [duststorms] up here. The reason why we are going on about [this one] is it was just so thick and black. It was dark red to black dust and it was thick as visibility was less than 20m for about 30 minutes then 100m for 6 hours after that. It was an amazing system because of colour and thickness, that is why we are going on about it and how everything is covered with a few millimetres of dust. Trees, grass, everything is brown."

Lameroo SA, Warracknabeal VIC and Hay NSW all reported severe duststorms with visibility of 100m or less around 3pm. The dust area moved across Melbourne during the afternoon, where the levels of dust in the air were among the highest ever measured and visibility was reduced to 3km.

Mildura Top Crop officer Daryl Pearl told ABC News that farmers would be counting the cost of the duststorms for many years. He said the wind blew away fragile topsoil and valuable nutrients from paddocks already suffering from drought, and farmers would now be looking for rain to settle the dust and return structure to the soil. But he added that the topsoil would be scattered over a wide area by the storm. "Anywhere from here to New Zealand, we'll top-dress a few paddocks along the way but we might end up giving something to the land of the long white cloud...we might turn it a bit orange, I think," he said.

Thunderstorms and rain. Two lines of thunderstorms produced torrential rain in SE SA and SW VIC during the day. The first developed along the troughline to the west of the Eyre Peninsula during the early morning and moved over the Adelaide area around 8am. Gusty winds and brief heavy rain caused peak hour traffic chaos with traffic lights knocked out and accidents blocking roads. The SES received 45 calls for help from Noarlunga in the south to Salisbury in the north as houses were flooded and trees brought down, including one that brought down powerlines, blocking the Glenelg tram service for most of the morning. Adelaide Airport recorded a top wind gust of 82km/h at 8.09am.

A second area of storms, packing torrential rain and storm force wind gusts, accompanied the low that developed on the cold front as it crossed the SE SA coast and moved into western VIC. The fast-moving storms produced some very high rainfall rates (see downpours below). Coonawarra recorded 15.2mm in 6 minutes to 1.54pm, and Mt Gambier airport 14.8mm in 17 minutes to 2.44pm. Robe reported 64mm between 9am and 3pm, the combined total of the morning and early afternoon storms. The heavy rain caused some flash flooding of homes in the Southeast, while squally winds brought down powerlines and trees, and contributed to a collision between a truck and a utility on the Bordertown to Naracoorte Road, seriously injuring the utility driver. Stock losses were reported, including over 1,000 sheep on a property near Penola and more than 150 sheep on another near Naracoorte.

As cool upper air combined with strongly converging winds around the developing low, the area of storms developed explosively as it moved into Victoria's West Coast and Western Plains. Hamilton airport recorded 32.6mm between 5 and 7pm with wind gusting to 89km/h at 6pm. An unofficial weather station 17km west of Hamilton recorded 86mm between 3.50 and 5.30pm, with rainfall rates as high as 223mm/hour and a storm event total of 110mm. 5cm hail fell early in the storm and flash flooding to 1.5m deep carried mud through the house at the station. Hamilton emergency crews received over 30 calls to assist at flooded buildings in and around the town. Similar conditions are likely to have occurred over a wide area, with official 24-hour rainfall totals to 9am Thursday including 83.2 at Casterton, 70.2 at Dunkeld and 61.6 at Warrnambool Airport.

The storms produced several new rainfall records (see also the records section for Thursday). Robe's 24-hour total to 9am Thursday of 67.6mm beat a previous March record of 56.1mm. What is significant is that Robe has an extraordinarily long rainfall record of 138 years. The 83.2mm reported at Casterton Showground was the stations highest fall for any 24-hour to 9am period since records began in 1956. Press reports indicate some very heavy unofficial rain measurements along the storm track to the ESE of Robe. The Kangaroo Inn Area School, 48km ESE of Robe, recorded 112mm for the 24 hours to 9am Thursday, while a gauge near Penola registered 94mm.

Another area of storms developed ahead of the front to the west of Melbourne mid-morning, then propagated east and southeast during the afternoon giving heavy rain to Tasmania's north coast and high winds through Melbourne, eastern VIC and northern TAS. Melbourne Airport recorded a gust of 91km/h at 8.53am and Mt Hotham summit recorded 113km/h at 4.30pm. Late in the evening, Cape Grim, on the northwestern tip of TAS, was reporting gusts to 130km/h at 11pm and midnight, with sustained speeds around 100km/h indicating that conditions in Bass Strait would have been far from comfortable. Lightning struck a tram as the storm passed through Melbourne causing a fire in its roof. Lightning also started a fire that burned through over 60 hectares near Gembrook in the Dandenongs.

For another article on this event, go to Stormplanet.