Predictions East Coast Rain Event 3-11 Feb 2020

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POW Hungry

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They had it up yesterday that coastal fringe could see thunderstorms. Not sure why they removed it.
Argh, I thought I saw it there yesterdee. I just noticed it’s in the Marine forecast. And with steering winds out of the E/NE (onshore 1000-700mb) we’ve got the fuse lit...
 

Snow Blowey

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For every 1mm of rain that is runnoff you get 1ML per 1km2 of catchment.

Warragamba Catcment is 9000km2. So for every 1mm you get 9000ML.

Dam capacity is circa 2,500,000ML.

2,500,000ML / 9,000ML = 278mm.

But Lake is already 42% full so you only need about 1,500,000ML to fill.

So only 167mm to fill.

Obviously very simple sums not taking in all the losses that have to occur before you get any runoff.

500mm widespread will see the spillway at work and lots of flooded wet folks in western sydney.
 
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Donza

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For every 1mm of rain that is runnoff you get 1ML per 1km2 of catchment.

Warragamba Catcment is 9000km2. So for every 1mm you get 9000ML.

Dam capacity is circa 2,500,000ML.

2,500,000ML / 9,000ML = 278mm.

But Lake is already 42% full so you only need about 1,500,000ML to fill.

So only 167mm to fill.

Obviously very simple sums not taking in all the losses that have to occur before you get any runoff.

500mm widespread will see the spillway at work and lots of flooded wet folks in western sydney.
I'm interested in Cordeux, Cataract and Avon
 
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Adaminaby Angler

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This looks like fun:

Access-G NSW 5-15.2.png
Blardy hell! Truly, that is rain of biblical proportions.
 

Undies

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For every 1mm of rain that is runnoff you get 1ML per 1km2 of catchment.

Warragamba Catcment is 9000km2. So for every 1mm you get 9000ML.

Dam capacity is circa 2,500,000ML.

2,500,000ML / 9,000ML = 278mm.

But Lake is already 42% full so you only need about 1,500,000ML to fill.

So only 167mm to fill.

Obviously very simple sums not taking in all the losses that have to occur before you get any runoff.

500mm widespread will see the spillway at work and lots of flooded wet folks in western sydney.

Cheers for that. Love a bit of maths.

There must need to be a good 20-30mm fall before the catchments start to fill, as this report from a couple of weeks back showed that even with fair falls across the catchments for the week the overall storage still dropped a tiny bit.

https://www.waternsw.com.au/__data/...nd-supply-report-Thursday-23-January-2020.pdf

The idea of having the dams full again certainly is appealing. Just hope that there's not too much erosion and subsequent algal blooms as a result.
 

MisterMxyzptlk

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Here on the Coast we had 200mm 2 weekends ago with surprisingly little runoff into the dams
Just showed how dry the ground was I guess
I think we'll get 50-100 out of this today/ tomorrow I'm expecting run-off to be a lot more
 

Snow Blowey

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Cheers for that. Love a bit of maths.

There must need to be a good 20-30mm fall before the catchments start to fill, as this report from a couple of weeks back showed that even with fair falls across the catchments for the week the overall storage still dropped a tiny bit.

https://www.waternsw.com.au/__data/...nd-supply-report-Thursday-23-January-2020.pdf

The idea of having the dams full again certainly is appealing. Just hope that there's not too much erosion and subsequent algal blooms as a result.


Its typically alot more than 20-30mm. BUt depends on catchment characteristics. For example, flat black soil plains in the NW slopes and plains absorb lots of water and are full of large deep cracks when dry. They may take a couple of hundred mm bt then everything goes after that. As opposed to rocky steep slopes along the ranges with enegligable soils and everything in between.

In 2016 we had the wettest winter on record in the central west NSW. There must have been half a dozen 20-40mm falls with next too no effect on the rivers and creek. Then on the seventh fall of 20mm everything just started gushing water everywhere and there was flooding every time we got a 20mm event in the two months afterwards. That was the season where Burrendong went from 10% to 140% in about 3 weeks. WOuld have been some very major flooding if the dam had have been full and the ground wet at the start of it all.
 

Majikthise

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Also depends on soil infiltration...in burnt areas likely lots more run off , less percolation into the ground at lower than normal rain intensities.
Eg 30 mm/h fall could shed 20mm/h because soil is flat out taking up 10mm/h . Prior to fire because of leaf litter and canopy soil may have been able to cope with 40mm/h ( not shed anything until field capacity was reached)
 

BlueHue

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Spent quite a few years in water quality monitoring targeting wet weather and definitely the case that a few good falls are often needed before run off really starts to crank - there is a lot of sub surface infiltration to take place first and vegetation certainly sucks up its share early on during drought. Their is some research however suggesting that bushfire effected ground can be water repellent leading to increased runoff in otherwise similar rainfall scenarios - I wonder now also if the drastic reduction in vegetation will also lead to a significant increase in runoff due to reduced uptake.
 

Snow Blowey

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It deserves to be mocked relentlessly. How often must it happen before they make a coding change?


I remember seeing a GFS forecast chart a few snow seasons ago that had many of us scoffing at the implausibility of the prediction and then it happened 7 days later.
 
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Ken Kato

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Above is a selection of various ensemble tracks out to 10 days colour-coded by intensity but using the Saffir-Simpson intensity scale (not ours).
Note though that the majority of those tracks visible on that map is from the EC ensemble because a lot of the 12z ensemble tracks weren't visible yet when I saved the screenshot.
Also of note is that the current system may not necessarily stay a TC for the entire lengths of the tracks due to the way the tracking algorithms work, and it's just as possible that it might experience some reintensification as a baroclinic system after it undergoes extratropical transition (if it makes it that far south that is).

But regardless of landfall or not, I don't think it's out of the question that there might be some reasonably powerful long-period swells developing later next week along the NSW and far southern QLD coast if one or more Coral Sea systems end up tracking south enough as a strong system and doesn't weaken beforehand or get whisked away to New Zealand first.
 

AshestoAshes

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Forecasts here aren't as impressive in my neck of woods but ECL-type rainfall totals without an ECL which is great, but imo even though the winds are often quite strong there's not really any damage. Flooding is the main threat, but all the creeks are quite empty a way to go. Feel like Chipping norton and other low-lying areas of the Georges River may be under threat given any rain trains.

Screen Shot 2020-02-06 at 4.39.44 pm.png
 

PeterM

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Bom really upped the totals for tomorrow in Sydney Metro, Sydney Trains are going to be fun tomorrow... I'd say flooding on some lines, it's happened before with way less than what is predicated for tomorrow.
 
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KylePee

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With an afternoon drive from Nth Sydney to kangaroo valley tomorrow I’m going to have to watch the impacts to decide route. M7 and Hume is feeling safest option. Would prefer coastal but too many places to go wrong I reckon
 
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Donza

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With an afternoon drive from Nth Sydney to kangaroo valley tomorrow I’m going to have to watch the impacts to decide route. M7 and Hume is feeling safest option. Would prefer coastal but too many places to go wrong I reckon
Kangaroo Valley may flood this weekend ........
Few causeways down that way as well
 

KylePee

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Personally I'd go mt ousley.
Though Tongara at Albion Park will close....
It’s even before the gong that’s playing bigger consideration. ED/airport area, bayside, not so much flooding but just Sydney in a Friday, plus throw some puddles or heavy rain and people forget to drive. M7/Hume should at least keep slowly moving... unless big crash that screws everything
 
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Donza

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Yeah true I guess. I've done the M7 in peak rain.
She can be a bit floody as well.

Play it by ear I guess.
 

Winterwolf

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500mm over the catchment could really bump the storage by 15%-20%.
Read somewhere Sydney water estimate is it's around 300mm catchment wide roughly in 24 to 48 hours to get a spill. Can't see that much even if Robertson gets 500mm.
 

rocketboy

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I remember seeing a GFS forecast chart a few snow seasons ago that had many of us scoffing at the implausibility of the prediction and then it happened 7 days later.

Was that the coastal storm that came down the coast and eventually end with a swarm of tornados coming ashore in Kiama and Shoalhaven Heads area that could have killed dozens with a slight change in storm tracks?
 

Belly

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Was that the coastal storm that came down the coast and eventually end with a swarm of tornados coming ashore in Kiama and Shoalhaven Heads area that could have killed dozens with a slight change in storm tracks?
If we're talking the same thing we call it the black NE'r event in surfing circles. It was June 2016.
 

Homer

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WOW! @ Penrith.

Penrith Forecast
View the current warnings for New South Wales

Forecast issued at 4:20 pm EDT on Thursday 6 February 2020.

Forecast for the rest of Thursday


Showers increasing.
Chance of any rain: 90%
rain_90.gif


Friday 7 February

Min 19
Max 22
Showers increasing, possibly heavy.
Possible rainfall: 50 to 100 mm
Chance of any rain: 100%
rain_100.gif


Saturday 8 February

Min 19
Max 23
Rain. Possible heavy falls.
Possible rainfall: 60 to 120 mm
Chance of any rain: 95%
rain_95.gif



Sunday 9 February

Min 20
Max 23
Rain. Possible heavy falls.
Possible rainfall: 70 to 150 mm
Chance of any rain: 95%
rain_95.gif


Monday 10 February

Min 20
Max 26
Rain. Possible heavy falls.
Possible rainfall: 15 to 50 mm
Chance of any rain: 95%
rain_95.gif

S

Tuesday 11 February

Min 20
Max 27
Showers.
Possible rainfall: 8 to 20 mm
Chance of any rain: 80%
rain_80.gif



Wednesday 12 February

Min 21
Max 28
Showers increasing.
Possible rainfall: 8 to 15 mm

Thursday 13 February

Min 21
Max 26
Shower or two.
Possible rainfall: 4 to 15 mm
Chance of any rain: 70%
rain_70.gif



The next routine forecast will be issued at 4:45 am EDT Friday.
 

Undies

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Not much fell here in the Inner West today. Hoping there's a bit more on the way for the catchment. Looks like there should be.
 

dawooduck

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It’s even before the gong that’s playing bigger consideration. ED/airport area, bayside, not so much flooding but just Sydney in a Friday, plus throw some puddles or heavy rain and people forget to drive. M7/Hume should at least keep slowly moving... unless big crash that screws everything

Always an "interesting" drive in a rainstorm.
 
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Wavey

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Geez 650mm at Albion Park would be a huge worry. Would cut off my suburb for sure.

Saturday has 80-200mm and Sunday 90-200mm.
 
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