NSW, QLD, VIC: Storms bring welcome - and not so welcome - rain
Thu 16 Jan 2020
Thunderstorms developed in and east of a low pressure trough lying from the Gulf of Carpentaria to VIC overnight Tuesday/Wednesday 14th/15th introducing five or six days of stormy weather for the eastern states. As usual with thunderstorms, rain was hit or miss with some sites recording torrential falls while others not far away received nothing, but for farmers in the firing line it was pure joy.
This was tempered, however, by the worry that heavy storm falls could cause severe erosion and mudslides in areas where bushfires had weakened soil and covered it with ash. Warnings of potentially blocked roads and contaminated streams became common in the Bureau's storm warnings. As the BoM's senior forecaster Rod Dickson told the SMH/Age‡, "Any thunderstorm with heavy rain in fire-affected areas has the potential to cause significant runoffs which picks up and ash and soil." Warnings were also issued by the Murray-Darling Basin Authority that storm runoff would wash ash and sediment into rivers leading to mass fish kills.
In VIC storms gave the heaviest rain in central parts and especially the Melbourne area on Wednesday 15th where it was heavy enough to cause flash flooding in western and NW suburbs. At St Albans 54mm fell in 30 minutes to 16:45 for a 24-hour total of 77mm. Avalon Airport E of Geelong recorded 44mm in 30 minutes to 15:30 as the trough came through, accompanied by a January record wind gust of 113km/h as a particularly dangerous thunderstorm moved across. The SES responded to nearly 600 call-outs across VIC during the day.
Lighter and patchy rain fell over the firegrounds in eastern VIC with the heaviest falls only between 15 and 20mm.
In NSW storms moved through western districts overnight Tuesday/Wednesday giving some places their heaviest rain since early November, including Wanaaring (Delta), 60km W of Bouke, 35.6mm and Wilcannia 16.6, though most places received nothing. Storms really began to develop on Thursday 16th, as the trough moved east into moist, unstable air nearer the coast. In the 24 hours to 09:00 Thursday Faulconbridge in the Blue Mountains recorded 48.0mm.
This radar grab of intense storms moving across the firegrounds in SE NSW between 13:00 and 14:00 AEDT Thursday shows how hit-and-miss they were.
On the firegrounds beneath, the rain helped with containment, but was a long way from extinguishing the fires and often made access difficult. Other problems arriving with the heavy storm rain included water contamination, with silt-trapping curtains and booms installed for Sydney's water supply at Warragamba Dam, and the first reports of a mass fish kill received on the Macleay River, NW of Kempsey.
In QLD storms brought rain in the west from the Gulf Country to SW QLD from Tuesday 14th, lifting spirits everywhere. Storms spread eastwards to bring the cheer to much of the state by Thursday. As in the southern states, storms often produced torrential rain where they occurred. Strathtyre Road, 80km SW of Toowoomba, for example recorded 64mm in the hour to 14:15 on Thursday 16th and went on to a 3-day total of 154mm by 09:00 Sunday 19th . This is more than most places in southern and SW QLD have recorded in the past 12 months.
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