Heavy rain, Floods, Storms and wind – NSW, QLD and NE Victoria – December 14 to December 19 2020

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Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020

A significant weather event has impacted eastern Australia between December 14 and December 19 2020 with the area stretching from South East Queensland, Eastern New South Wales and into North East Victoria being most affected.

In particular, flooding rains has impacted north east New South Wales around the Bellinger Valley, Coffs Harbour Region, Grafton, the Tweed River Valley and South East Queensland while thunderstorms have impacted much of eastern New South Wales which has included localised heavy falls, damaging winds and hail. As usual, thunderstorms are often hit and miss and rainfall totals have varied considerably.

Damage along the coast has been significant which has included beaches being washed away or covered in foam, property damage and roads being washed away. There was also a landslide on the Dorrigo Road between Dorrigo and Bellingen.

At the present time, the cost of the weather events are being tallied.

As shown in the attached plots prepared on the Bureau of Meteorology "Water and the Land" sites, the heaviest falls have been around the Tweed River Valleys and the Bellinger Valley including the Coffs Harbour Region.

Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020
Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020

On the 14/12/2020, significant rainfalls impacted the Sunshine coast and its hinterland with many locales receiving more than 100 mm of rain.

Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020

At the local level, some of the rainfall totals have been significant. A weather station at Upper Springbrook (Queensland) recorded 952 mm of rain during this event which exceeds the average annual rainfall for cities such as Melbourne, Perth, Canberra and Adelaide.

Some rainfall totals include:-

1 - Grafton - 13/12/2020 - 79.6 mm, 15/12/2020 - 125.2 mm and the 17/12/2020 - 99 mm. As at 20/12/2020, 477.6 mm of rain has fallen at Grafton which is far in excess of the average December average of 91.4 mm.

2 - At Coffs Harbour Airport, 12/12/2020 - 150.6 mm, 15/12/2020 - 73.8 mm and the 16/12/2020 - 116.2 mm of rain fell.

3 - At Dorrigo which is close to the wettest location in New South Wales, 435 mm of rain has fallen between December 1 and December 20 2020. This takes the yearly rainfall to date to 2,344 mm which is well in excess of the average to December of 2,013.5 mm.

4 - At Bellingen in the Bellinger Valley, a rain gauge recorded 220 mm of rain during one these events. The topography of the Bellinger Valley often enhances the rainfall.

5 - On December 17 2020 at Lismore (NSW), 202.8 mm of rain fell which resulted in riverine flooding and evacuations. As at December 20, 2020, Lismore has received 484.2 mm of rain which is well in excess of the usual December average of 121.9 mm.

This is showing the scale of the event. While the heavy rain and flooding is generally limited to north east New South Wales and south east Queensland, thunderstorms have impacted large areas of inland New South Wales including the Sydney region which has delivered localised but significant rainfall totals. Samples include:-

1 - Albury (NSW / Victorian state border) - A single thunderstorm event between 11 pm and 3 am on the 16/17 December 2020 dropped 50.2 mm of rain including 18 mm during the period 1.05 am and 1.30 am. The same storm system produced 42 mm of rain at nearby Barnwartha to the west.

2 - Dubbo - Storms dropped 26.8 mm of rain on the 17/12/2020.

3 - Gunnedah (North west slopes and plans of New South Wales) 17 - 18 December 2020 - Storms delivered rainfall totals of 36.2 mm and 41 mm and peak wind gusts of 98 km/h. Those gusts occurred during a brief period between 4.20 pm and 4.28 pm on the 18/12/2020.

One such storm on Thursday afternoon 17/12/2020 impacted parts of Western Sydney as shown in the attached photo. This storm was slow moving and approached Blacktown from the south although at sunset, the storm cell went into sharp decline. During its most active phase, the storm was producing strong updraft towers, numerous cloud to ground lightning strikes and an interesting rain free base. There was little evidence of the storm cell after sunset due to its rapid decline.

Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020
Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020
Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020
Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020

On Friday afternoon, a short sharp rain shower developed over Western Sydney although no lightning was observed from this cell. A rainbow was later photographed.

Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020

The photos attached to this post of the Thursday afternoon storm were taken from a park looking south from Blacktown.

Heavy rain, Floods, Storms and wind - NSW, QLD and NE Victoria - December 14 to December 19 2020

Heavy rain and flooding NE NSW and SE Qld 11 to 14 December 2020

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Heavy rain and flooding NE NSW and SE Qld 11 to 14 December 2020

A significant rain event rain across the coastal regions of north east New South Wales and South east Queensland has been unfolding and the event is likely to continue for the next few days.

The event has been coastal in nature with the rain reaching the eastern side of the Great Dividing Range but not penetrating westwards into the inland areas. As at Sunday morning 13/12/2020, very little rain has penetrated inland and during the same time, very little rain has moved southwards of the Mid North Coast.

Heavy rain and flooding NE NSW and SE Qld 11 to 14 December 2020

In Particular and for the 24 hours to 9 am 12/12/2020, the heaviest rainfall occurred around Coffs Harbour and the nearby Bellinger Valley. It is likely that the surrounding hills intensified the rainfall due to orographic processes with the heaviest rainfall being concentrated to localities within the valley but east of Point Lookout.

Heavy rain and flooding NE NSW and SE Qld 11 to 14 December 2020

The heaviest rain includes 203 mm at Bowraville and 161 mm at Bellinger. Coffs Harbours was drenched with rainfall reaching 150 mm up to 156 mm.

Another location on the mid north coast being Logans Crossing received 187 mm.

For the 24 hours to 9 am 13/12/2020, some exceptional rainfall totals have occurred within the Tweed River Valley areas and south east Queensland including the Gold Coast city area.

For New South Wales, the heaviest rainfall includes - Tweeds Heads - 253 mm, Bray Park - 250 mm, Uki - 211 mm and Repentance - 182 mm. Most localities within the Tweed River Valley has been drenched with flooding likely.

Heavy rain and flooding NE NSW and SE Qld 11 to 14 December 2020

In south East Queensland, some exceptional rainfall totals for the same period includes Upper Springbrook Alert - 475 mm, Tomewin Alert - 370 mm and Tallebudgera - 346 mm. Such totals and others are confined to areas just south of Brisbane encompassing all the Gold Coast City areas and its hinterland.

Heavy rain and flooding NE NSW and SE Qld 11 to 14 December 2020

The forecast models continues to suggest further heavy rain which has potential to cause further flooding. Some of this rainfall is expected to drift further south towards Sydney later in the week although such high totals are not expected. While some models suggest that some moderate rainfall will make its way into the eastern inland New South Wales, other models are suggesting that only light falls are likely to occur with the heaviest falls being concentrated to coastal areas north of Sydney.

Tuesday afternoon storms with small hail 1/12/2020

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Tuesday afternoon storms with small hail 1/12/2020

The weather across Sydney 1/12/2020 turned out to be a day of remarkable contrasts. A cloudy morning was following by a long period of heating and sunshine which was then followed by a dramatic late afternoon / evening thunderstorm that produced small hail.

The maximum daytime temperatures occurred late in the day as a result of what occurred. It reached a maximum of 38.5C in Penrith, followed by 38.1C at Richmond, 35C at Blacktown and Horsley Park and 33.6C at Parramatta. It was cooler further east.

Late afternoon, a thunderstorm crossed over much of Sydney and while rainfall totals were not significant (Between 7 and 14 mm of rain), it had a dramatic impact.

Tuesday afternoon storms with small hail 1/12/2020
Tuesday afternoon storms with small hail 1/12/2020

The storm event produced maximum peak wind gusts of 106 km/h at Richmond which was enough to bring down trees. Peak wind gusts reached 83 km/h at Penrith between 6.38 pm and 6.47 pm. In addition, lightning strikes caused some power outages and one bell tower attached to a house in Ashfield appears to have been struck by lightning which caused a fire but it was contained to the bell tower structure.

Tuesday afternoon storms with small hail 1/12/2020
Tuesday afternoon storms with small hail 1/12/2020

Over Blacktown, a small storm cell formed ahead of the main line of storms which produced small hail in the range of 0.5 mm to 0.9 mm in diameter. My wife and I were able to collect these using a plate before they melted. This storm cell also produced a sharp but brief downburst accompanied with a short heavy burst of rain. This storm cell eventually merged with other storms as the system passed across Sydney. The main line of storms followed shortly afterwards which produced rain and some wind.

Tuesday afternoon storms with small hail 1/12/2020

Photos of the event are showing developing storms ahead of the main line followed by an interesting storm base. Much of the lightning was within cloud although there were the occasional cloud to ground strikes. The storms were fast moving and all activity had cleared by sunset.

Tuesday afternoon storms with small hail 1/12/2020
Tuesday afternoon storms with small hail 1/12/2020
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