QLD, NT, WA: Thunderstorms, troughs and a tropical low bring floods, heavy rain, and some incredible totals to N Australia
Wed 29 Jan 2020  

Much of the northern half of QLD had 100 to 200mm rain in the week to 09:00 Wednesday 29 January, but many pockets of 300 to over 500mm have caused flash flooding and some wide areas of inundation. BoM .

Monsoon-like conditions have brought heavy rain across large parts of northern Australia in the past 10 days or so, with thunderstorms, trough lines and a nearly stationary tropical low all making maximum use of plentiful moisture feeding in from the NW and N of Australia.

In the week to 09:00 Monday 27th the highest totals were in an area around Darwin, where Gunn Point recorded 299.6mm and Howard Springs 295.0, but a broad swath of Northern Australia from the North Kimberley, across the NT Top End to central and northern QLD recorded 50 to 150mm with some much higher isolated falls.

On Tuesday and early Wednesday 28th/29th, however, there were some phenomenal rainfall totals on the QLD Central and Tropical North Coasts. Stations around Ayr, ESE of Townsville, recorded around half a metre of rain in the 24 hour to 09:00 29th.

Rita Island, at the Burdekin River mouth just ESE of Ayr topscored with 529mm as a convergence line moved over the area and just sat there for nearly 9 hours. Their rainfall for the hour to 03:00 on the 28th was 26mm followed by successive hourly readings of 38, 49, 57, 72, 70, 64, 44 and 42 to 11:00 28th after which the rain stopped.

Ayr itself recorded 421mm while nearby Ayr DPI's seemingly modest 24-hour total of 327.8 was an all-time record in its 70-year history. Some other sites with shorter histories also set all-time records. Here are the top falls and their distribution:

These satellite animations from Andrew Miskelly - first with standard visible light imagery followed by water vapour imagery showing moisture - dramatically show the main cause of the rain: abundant moisture being pulled in from the north around a low that was in far NW QLD at the time.

The low, a trough down through W QLD, the moisture and instability combined to produce torrential thunderstom falls in NW and W QLD, with many places picking up over 100mm in one hit. Both Normanton and Winton set new all-time records for one-day rain to 09:00 28th at their airport sites with 154.4 and 117.4mm respectively. A grazier from Winton Downs, 60km S of Winton, who was interviewed on the Country Hour had had two such dumps on consecutive days - 205mm on the 27th and 126 on the 28th. Winton Downs isn't a BoM official or flood station so timing and standards are unknown, but the time of the broadcast at noon suggested readings were taken around 09:00 ± a few hours.

Flooding is bringing back raw memories of the disastrous floods in February/March 2019, with several rivers that drain into Lake Eyre and the Gulf already at moderate flood level in places. However as the weekly rain map above shows, broadscale rainfall hasn't been anywhere near the same amount. This ABC article gives extensive and detailed coverage of the impact of the rain and floods in N and NW QLD, while Mount Isa's North West Star* gave practical information for NW QLD, like a long list of roads closed or affected by flooding or rain. The BoM's Weekly Rainfall Update gives a detailed analysis of the rain, its causes and its impact on drought conditions.

For heart-stopping moments, though, you can't beat the view the crew on this goods train from Townsville would have had as they approached this small bridge at Prairie, just east of Hughenden - and only just stopped in time.

 AWN changes for 2020
Wed 22 Jan 2020

I have made changes to the OCF forecasts, this blog and the Daily Weather Summary (DWS) for 2020. The DWS is popular for its archive of maps, statistics and information on past days' weather going back to before 2000. The current day's DWS also gives a handy overview of weather around the country as it gradually fills with information through the day.

The changes are:

• Temperature, rainfall and wind records are important signs that the weather is way beyond normal. Heatwaves since the beginning of January have seen hundreds of towns set new records for hot days and nights. Unfortunately, what looks like a record could just be an error and the BoM's quality control system can take time to pick it up. I have improved AWN's own quality control system which is not as thorough as the Bureau's but identifies most data problems within a day or two. Information on how this works is at the top of the records section of the DWS, such as here, and you can see that additional information is often put in the comments column.
• The system I use for gathering weather news information has been upgraded and the sources refined to the most reliable ones. The descriptions of daily weather events that go in the blog are then put in the relevant day's DWS as a permanent record of that day's weather.
• Finally, each location for which OCF forecasts are given now has a Map link in the black bar beside its name. OCF forecasts are given for locations that correspond with BoM weather stations so the temperatures, rainfall, etc., can be verified. The link takes you a map showing the location of the BoM weather station, marked with a red pin - zoom out to see the surrounding town and area.

 NSW, QLD, VIC: Storms bring welcome - and not so welcome - rain
Thu 16 Jan 2020   NOTE DATE: ARCHIVE STORY  

Thunderstorms developed in and east of a low pressure trough lying from the Gulf of Carpentaria to VIC overnight Tuesday/Wednesday 14^th/15^th 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 15^th 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 16^th, 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 14^th, 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 16^th and went on to a 3-day total of 154mm by 09:00 Sunday 19^th . This is more than most places in southern and SW QLD have recorded in the past 12 months.