NSW/ACT Widespread Rain - August 7-10, 2020

Steve777

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A low has formed over Central Australia bringing, welcome rainfall to SA and the Southern NT. The low is expected to intensify and move South-Eastwards, bringing widespread rainfall, with 25 mm+ expected over most of NSW. The low will escape into the Tasman on Sunday, possibly to become an ECL.

Here’s the forecast synoptic chart for 10:00 tomorrow. Not often that you see a mid-latitude style depression complete with a cold and warm front over the Australian mainland.

8FBD3E46-6F25-4936-8A94-758D023EAC72.png


Heavist falls are again expected on the NSW South Coast. The BOM are forecasting 80-180 mm for Batemans Bay over the following seven days. Rainfall decreases Northwards, with Sydney now expecting about 30-65 mm, less than was anticipated a couple of days ago. Inland, Forbes is expecting about 15-30 mm.

Here’s the forecast rainfall for the 8 days August 6-13 according to the BOM this morning:

1C7E50F8-A8A7-4458-A640-130AAB867FC2.png
 

Homer

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Thanks for starting this Steve.

Yes, it may not be a big deal here in Sydney Town, but further south looks to get hammered again.
The alps look to do particularly well for snow, albeit it might be a bit wet and not the dry snow they prefer. Looks like it could be a metre plus of the wet white stuff.
It will be interesting to see what happens at Brown Mountain/Nimmitabel and the Snowy Mountains Hwy around that region. 200-300 mm's forecast for there according to your map!!!

Also, between Cooma and Jindabyne could be a mess on the roads as well. Temps look a degree or two colder than the last similar event two weeks ago.

As for the coast, Bega is looking at a max rainfall of 300+. (174 - 310!!)

I love the forecast rainfall chart you posted. All of NSW receiving precip during that period, with a large chunk in the 15-50 mm range.
This will be a fascinating system to watch.

BOM 4 Dayer below.

IDG00074.gif
 

Steve777

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There have been widespread falls in the range 10-20 mm over the Western half of the State, with a number of falls over 25 mm, for example around Bourke - much welcome I'm sure. Areas further East received falls around 2-8 mm.

After no rain overnight, Sydney OH had a millimetre between 9:00 and 9:10 from a small cell moving in from the East. The main rainband is moving down from the North-North West and might be here by late morning.
 
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Undies

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Any predicted totals for Sydney over the weekend? Am just wondering whether kids sports will be cancelled.
 

Homer

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Any predicted totals for Sydney over the weekend? Am just wondering whether kids sports will be cancelled.

I'm wondering that myself.
All I'm going by at the moment is BOM's predicted totals.
It'll depend I suppose how much rain we get today/overnight.
 

Steve777

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That's 'snow - Blue Mountains??'LOL
No. The cold air stays West and South, so plenty of snow for the Snowies, even some in the Flinders Ranges but the air mass over the Central Tablelands is too warm. The current temperature at Mt Boyce is about 6°.

====
There’s been persistent light rain since mid morning. Sydney OH has had 5 mm since 9:00 which seems to be typical for the Metro area. Chatswood has had 9 mm.
 

Flowin

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The Bureau recently upgraded their 7 day streamflow forecasting service to produce probabilistic hourly streamflow forecasts for some catchments.
Note the forecast rainfall will differ from what you see for a forecast location, because they provide estimates of rainfall over a catchment area rather than rainfall at a point. It also applies complex bias correction methods.
I have been watching the service through the last ECL a couple of weeks ago - have mixed views about whether the bias correction may be too much diminishing of the median amount expected on catchments. Example below.
Note it is a streamflow forecast - not necessarily suited to a purpose for a flood forecast (very fuzzy boundary though as I am sure they may get misinterpreted)
215208_acc_rain_ens.png


215208_hourly_barplot_ens.png
 

Steve777

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There’s a distinct clearing edge to the rain band approaching Sydney from the NW. Also a distinct clearing edge to the thicker part of the cloud band, extending from about Newcastle SW into the Riverina, although there’s low cloud underneath.

The visible satellite picture indicates that the low is located about half way between Cobar and Invanho.
 

Homer

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Bega forecast for rain is 200 - 350 mm over next two days. They need that much?

Nowhere needs that much in two days. Ever.

Nice steady rain here today once it started. As Steve said, there's now a clearing edge which is almost upon me here.
Very eerie looking earlier. It's been very foggy here since about 3 pm, and as this clearing edge approached, there must have been some clearing in the higher cloud, although I couldn't see it due to the lower cloud and fog. What it did do is cast an orange glow through the cloud and fog.
It looked very much like those very smoky bushfire days this past summer. Only difference was it was raining and 10 deg's. It was quite surreal.
 

AshestoAshes

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Nowhere needs that much in two days. Ever.

Nice steady rain here today once it started. As Steve said, there's now a clearing edge which is almost upon me here.
Very eerie looking earlier. It's been very foggy here since about 3 pm, and as this clearing edge approached, there must have been some clearing in the higher cloud, although I couldn't see it due to the lower cloud and fog. What it did do is cast an orange glow through the cloud and fog.
It looked very much like those very smoky bushfire days this past summer. Only difference was it was raining and 10 deg's. It was quite surreal.
Was really heavy around 4:15 visibility dropped to about 400metres as well, not keen for the potholes after this.
 
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Donza

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I've got a feeling we may seen some storms in the basin Saturday arvo
 
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Homer

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I've got a feeling we may seen some storms in the basin Saturday arvo

I agree, maybe even earlier.

Anyway, just when I thought the clearing edge was near, there has been some strange back building of showers on the radar and it is still raining.
Looks like the rain might last for a while yet.
 
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Donza

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I agree, maybe even earlier.

Anyway, just when I thought the clearing edge was near, there has been some strange back building of showers on the radar and it is still raining.
Looks like the rain might last for a while yet.
It's stopped in Wollongong... Radar still keen though.
 
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Steve777

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It’s a foggy start this morning. Webcams show near-whiteout conditions on the Harbour. The rain’s stopped, in fact in hasn’t rained at OH since 10:00 PM. Most of Sydney has received between 12 and 20 mm since 9:00, with falls over 25 mm in the East and South. The focus of the rain has been the Illawarra, with 131 mm at Nowra.

There are lightning-active cells way out to sea off Sydney and smaller cells on the Illawarra coast. I think it’s blue sky here above the fog, however.
 

Donza

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Wollongong being effected by some onshore cells.
Heavy showers in some areas with localised flooding.
 

Steve777

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Yesterday‘s maximum of 13.6° at Sydney OH was its coldest in over four years. Most Sydney sites maxed around 13-14°, with some sites in Sydney’s West ‘losing’ low maxima through the 9:00 reset, e.g. Richmond’s 10.8 (from memory) became 12.3°.

The sun’s out now. Turns out there was broken mid-level cloud above the fog. Those cells are still hovering over the Illawarra coast and there’s a substantial-looking rain band about to enter the Hunter region from the North. Things might get interesting later.
 
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Donza

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Yesterday‘s maximum of 13.6° at Sydney OH was its coldest in over four years. Most Sydney sites maxed around 13-14°, with some sites in Sydney’s West ‘losing’ low maxima through the 9:00 reset, e.g. Richmond’s 10.8 (from memory) became 12.3°.

The sun’s out now. Turns out there was broken mid-level cloud above the fog. Those cells are still hovering over the Illawarra coast and there’s a substantial-looking rain band about to enter the Hunter region from the North. Things might get interesting later.
Thankfully the wind has picked up here now. Some of those cells were just bucketing down on the Illawarra.
 
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Steve777

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Issued at 10:37 for Wollongong and Bowral to the Victorian border:

Severe Weather Warning
for HEAVY RAINFALL and DAMAGING WINDS

For people in South Coast and parts of Illawarra, Southern Tablelands and Snowy Mountains Forecast Districts.

HEAVY RAINFALL, which may lead to FLASH FLOODING and RIVERINE FLOODING, is forecast for the South Coast and Illawarra districts, and eastern parts of the Snowy Mountains and Southern Tablelands districts today and Sunday.
 
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Homer

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Had some nice sunshine here this afternoon after the lunchtime showers cleared away. The remainder of the cloud clear by about 3 pm so there was about an hour or so of sunshine.
I have however noticed quite a build up of cloud (with some decent looking cu's) in the last half an hour or so to my north and west. I notice the BOM still have the chance of a storm in the forecast.
We'll see what happens.
Rain off the coast is heading south while the current rain inland is heading north. Centre of the low, or a low, looks to be around Appin at present.

It became unexpectedly cold today, after what felt like quite a warm morning.
 

Homer

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Couple of rumbles of thunder here so far. Distant yet audible. Actually, a few more while I've been typing.
Just about to get the heavy rain.
Cold enough for some pea sized hail possibly.
 
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Donza

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Radar showing some really strange shit for the Metro and Illawarra atm.
Some quite random stuff showing up at will.
This.
I'll honestly say. I've not seen before.

I say I've seen similar (Ish) during the February 2013 tornado that hit kiama
 
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