Day to Day Sunday 10th - Friday 15th October 2021 Troughs and Fronts Eastern Seaboard

Mcbobbings

Hard Yards
Jul 10, 2019
77
173
83
Macquarie Park NSW
Sydney’s Spring weather is can be very changeable. It’s the beginning of the storm season. Winter-style cold fronts still get through. We get cold outbreaks in September, October, even November. It has snowed in the Blue Mountains in mid October a couple of times in recent years. We get outbreaks of heat. Near the coast, the hottest day of the season might be in November, even October. It’s just the nature of the beast.

EDIT: just started raining fairly heavily.

Perfect example of that is last November. Coldest temp was 15.6, hottest was two back to back days above 40 (40.8, 40.5) which was the first time that had happened in any month since the 30s. Those days above 40 were also the hottest days for the whole summer for Sydney. Rest of Summer, particularly December, was was wet, warm and bordering on mild for some parts.
 
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Donza

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Perfect example of that is last November. Coldest temp was 15.6, hottest was two back to back days above 40 (40.8, 40.5) which was the first time that had happened in any month since the 30s. Those days above 40 were also the hottest days for the whole summer for Sydney. Rest of Summer, particularly December, was was wet, warm and bordering on mild for some parts.
Indeed.
When we moved to Sydney...got off the aircraft to 11 degrees. WTF. Coming from a warmish Auckland.
Checked the records.
12.6 on 16/11/1988
 

Gleno71

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Jul 4, 2019
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Perfect example of that is last November. Coldest temp was 15.6, hottest was two back to back days above 40 (40.8, 40.5) which was the first time that had happened in any month since the 30s. Those days above 40 were also the hottest days for the whole summer for Sydney. Rest of Summer, particularly December, was was wet, warm and bordering on mild for some parts.
I wonder why Sydney can never have a sustained dry period, like 3-4 months of straight fine weather ??
 

Gleno71

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Jul 4, 2019
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What do you guys think are the chances of Eastern Sydney getting a good storm tomorrow?
The forecast max of only 24 is worrying me.
looks pretty good to me, dont always need heat if the atmosphere is really unstable like this Access G chart is suggesting for tomorrow Afternoon. K-Index ,LI ,CAPE , SWEAT showing high values. Sounding shows some turning with height in lower levels if im reading it correctly. @Ken Kato might have further insight. I think northern NSW also in for a show

instability--storm__potential__bom_syd.3deg_t17_00-042-2021101212z.png
Sounding.png
Screenshot 2021-10-13 08.15.34.png
 

davidg

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Feb 4, 2009
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The last 2 days in Penrith have both been the coldest October days since the AWS was brought online in 1994. The previous record was 15c in 2004 so a pretty soft record but still. Monday only reached 14.2c and Tuesday struggled to 14.7c, today could be cooler still, currently 12.4c and light rain falling. Pretty remarkable run of cold weather for October.

We've also have about 25mm of rain from this event here in Glenbrook. It has been a very welcome follow up from those storms 2 weeks ago after quite a dry September.
 

davidg

Part of the Furniture
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The last 2 days in Penrith have both been the coldest October days since the AWS was brought online in 1994. The previous record was 15c in 2004 so a pretty soft record but still. Monday only reached 14.2c and Tuesday struggled to 14.7c, today could be cooler still, currently 12.4c and light rain falling. Pretty remarkable run of cold weather for October.

We've also have about 25mm of rain from this event here in Glenbrook. It has been a very welcome follow up from those storms 2 weeks ago after quite a dry September.
Further to this, Richmond only managed to get to 13.6c on Monday. Looking at the Richmond UWS site for a better historical perspective, this would put it right up there with one of the coldest October days since 1881!


Record for that site was 13.5c back in 1973. Obviously difficult to directly compare sites but even still that is very impressive.
 
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Jimi

Early Days
Sep 10, 2021
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Roseville
Same here. It seems like the Hornsby Plateau is doing a great job of squeezing out more moisture than it really has any right to based on the light echos on the radar. It is steady, almost moderate rain here and has been for some time. Everything is quite drenched.
 

Joshua Randazzo

Hard Yards
Jan 1, 2021
259
233
63
near sydney CBD.
looks pretty good to me, dont always need heat if the atmosphere is really unstable like this Access G chart is suggesting for tomorrow Afternoon. K-Index ,LI ,CAPE , SWEAT showing high values. Sounding shows some turning with height in lower levels if im reading it correctly. @Ken Kato might have further insight. I think northern NSW also in for a show

instability--storm__potential__bom_syd.3deg_t17_00-042-2021101212z.png
Sounding.png
Screenshot 2021-10-13 08.15.34.png
wow cape strongest on the coast you don't see that often
 

Edge72

Hard Yards
Apr 3, 2020
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191
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Sydney
But the steering winds are from the north west and in my experience storms don't like coming off the rangers from the north west but with the amount of instability hopefully they make it
Some of the biggest storms to hit my area have come from a North West direction, so it can happen. I find they tend to last longer once of the ranges as opposed to storms that come in from the more common South West direction , at least for my area but i am located more to the south of the greater sydney area.
 

Snow Blowey

Old n' Crusty
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Jan 7, 2004
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Has been chilly in central NSW for the last couple of days. Sun came out a couple of hours ago after cold mizzle this morning. Went from running the heater to running the air con in the space of about an hour.
 

Gleno71

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Jul 4, 2019
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I think tomorrow's storm potential will be at least near the level of December 20th 2018.
Even tornados possible according to Karl Lijnders due to winds in atmosphere
On his membership website he has posted a Tornado map which suggest a strong chance. Could be based on the last event when we had a few touchdowns in the rural regions.
 
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Homer

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Aug 3, 2005
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So what are the more learned thoughts on the timing of tomorrow's storms. @POW Hungry @Ken Kato
I'm actually thinking that it will be dry tomorrow morning. Just unsure of the timing of any rain and storms after that. The Sat pic currently is a dog's breakfast. Still plenty of moisture and low cloud heading down from the north over eastern NSW. High cloud is drifting over that from the west. The, we have that arc of a cloud band entering the west of the state.

I ask, because my boss is hassling me about timing of the rain, as he is trying to plan the day. He thinks I'm the expert on weather!! lol.
It's such a dynamic situation tomorrow and I completely understand that predicted timings are not perfect nor should be relied upon.
Any help would be appreciated.
 
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Jasper Schwarz

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Jun 18, 2017
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I ask, because my boss is hassling me about timing of the rain, as he is trying to plan the day. He thinks I'm the expert on weather!! lol.
NGL.
Exactly the same situation at my work. I just repeat what those who are far more educated than me say and use that.
Makes me feel good others do the same ;)
 

Homer

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NGL.
Exactly the same situation at my work. I just repeat what those who are far more educated than me say and use that.
Makes me feel good others do the same ;)

Well, on Monday, I didn't think today was going to be as wet and drizzly as it was. Nor yesterday actually. And on Sunday, nor did the BOM!!
The pressure is on at work to produce the perfect forecast!! :nerd:

I do the same as you. I use the information I gain here, but I also apply a little bit of life long experience and keep a sharp eye on current obs (radar, sat pics and AWS obs) as well.
 

POW Hungry

Old n' Crusty
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So what are the more learned thoughts on the timing of tomorrow's storms. @POW Hungry @Ken Kato
I'm actually thinking that it will be dry tomorrow morning. Just unsure of the timing of any rain and storms after that. The Sat pic currently is a dog's breakfast. Still plenty of moisture and low cloud heading down from the north over eastern NSW. High cloud is drifting over that from the west. The, we have that arc of a cloud band entering the west of the state.

I ask, because my boss is hassling me about timing of the rain, as he is trying to plan the day. He thinks I'm the expert on weather!! lol.
It's such a dynamic situation tomorrow and I completely understand that predicted timings are not perfect nor should be relied upon.
Any help would be appreciated.
Looking like showery stuff from around 9/10am in the basin.
IMO we’ll see some cells in the basin around mid arvo.
Bit of pot luck if they get anywhere near severe IMO.
 
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Ken Kato

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Jul 13, 2019
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Did a post on social media earlier containing my thoughts about Thu/Fri so will copy and paste it here for interest's sake.
A fair bit of it focuses on SE QLD but some of it's also applicable to the broader eastern NSW/southern QLD region as well). The overall setup's still looking darn impressive for many areas, although there are still those complicating factors mentioned below that might throw a spanner in the works for some other areas:


Even though obviously not every person in the coloured areas on these maps is going to get a big storm or good rainfall, this is a very potent setup and likely to cause a widespread thunderstorm outbreak across large sections of SE, E, and N Australia on Thursday into part of Friday, with severe storms highly likely in at least some portions of these areas...... some could also get a particularly nasty supercell (with damaging to briefly destructive winds, large to locally giant hail, and bursts of intense rainfall). These types of setups can also sometimes produce the odd destructive tornado in the more favoured areas although not all of them do.

Showers/storms could start affecting some portions of SEQ (the SE Coast district) as early as overnight tonight or Thursday morning if the strong steering winds above us can manage to drag inland storms to the coast..... so don't be surprised if some of you get an abrupt early wakeup call from thunder or some downpours.

Although the bulk of any rainfall in SEQ should mainly favour Thursday morning (the activity in the afternoon being more in the form of shorter bursts) as well as Friday morning, some shower or storms activity will be possible at any time of day or night until Friday in SEQ. This is due to the increasing background destabilisation from the upper trough (showers may occasionally tend to rain areas as well)..... but it's not going to be storming or raining for every hour of the day.


TECHNICAL NOTES:

Most aspects of this setup are highly supportive of widespread storms in the more favoured areas with a number being severe. No shortage of shear, instability and moisture. This is also combined with some directional and speed shear in the lowest level of the atmosphere which means the potential for a localised tornado somewhere can’t be ruled out.

But it's still definitely worth keeping a few potential complicating factors in the back of the mind i.e. in the areas where there’s too much pre-existing morning cloud cover, rainfall, or storms that hangs around well into the afternoon without any clearer breaks, storms later in the day are unlikely to be as severe or widespread.

Also, as is often the case with these high-end multiday setups, there's always the possibility that in some areas, there's too many showers/storms which mass up into a cloudy rainy band early on (taking the edge off the severity of storms in those areas)…. and last into the next morning which then affects the potential the next day in those areas.

Also keep an eye on the rear edge of any cloudbands moving out of an area since storms can often fire up in that zone, even if that cloudband's been sitting over that area in the morning.

Friday afternoon is also a complicated one to forecast for SEQ because a) if showers and storms last into Friday morning, we'd have to have enough patches of clearer sky to then open up to help with heating for storms and b) if the drier westerlies sweep right through to the coastal fringe early on, this would mean most storm potential ends before the afternoon.

This last point is particularly critical because even the tiniest of shifts in the boundary between the dry westerlies and moist northerlies ahead of them can make all the difference between big crisp-looking cumulonimbus clouds exploding along the coastline (often nicknamed "nukes" in weather-speak) and nothing at all.

At this stage, guidance suggests storm potential may become more localised as we head further into the afternoon before dissipating but it'll need to be monitored closely just in case this changes, or if lingering moisture with the upper level trough and cold air aloft can pull a rabbit out of the hat.

Here’s a couple of thunderstorm potential maps generated by data from one of the models for the period covering the combined Thursday to Friday period (both maps are for that same period). But remember, storms won’t affect every coloured area on both days – this is just the max potential achieved during that period by these maps:



51584135724_67d083fa18_b.jpg
 

Ken Kato

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Jul 13, 2019
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Right on cue, thundery rain here started during the wee small dark hours of this morning and it's been continuing ever since. Moderate to heavy at times with the occasional lightning and thunder.
The models nailed it.

Severe thunderstorm warnings started being issued late last night while the activity was firing up over the Downs, and are still in effect as it's moved further east.
I also saw a chaser managed to get photos of what he described as a supercell at 3am.


1634154536767.png
 

POW Hungry

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Here are the SL dew points highlighting the trough (click for larger image).
Screen Shot 2021-10-14 at 7.22.20 am.png
I mentioned on Monday that it looked quite 'frontal' and BOM's latest chart has the front extending right up to ~ Bunderberg, not often you see that sort of extension. Near stationary by tonight.

Very impressive shear profiles today.

Screen Shot 2021-10-14 at 7.30.22 am.png


Looking at things a little more closely for Sydney this afternoon, my gut feel is that cloud and overshoot is going to suppress a lot of it for us.

That said, I think we'll see a decent rumble in the basin circa 14-1700 hours.

There's umpteens of instab, so if it gets going, there won't be much to slow it down so keep an eye on the radar in case you want to park your car undercover IMO.
 

Ken Kato

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Jul 13, 2019
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Here are the SL dew points highlighting the trough (click for larger image).
Screen Shot 2021-10-14 at 7.22.20 am.png
I mentioned on Monday that it looked quite 'frontal' and BOM's latest chart has the front extending right up to ~ Bunderberg, not often you see that sort of extension. Near stationary by tonight.

Very impressive shear profiles today.

Screen Shot 2021-10-14 at 7.30.22 am.png


Looking at things a little more closely for Sydney this afternoon, my gut feel is that cloud and overshoot is going to suppress a lot of it for us.

That said, I think we'll see a decent rumble in the basin circa 14-1700 hours.

There's umpteens of instab, so if it gets going, there won't be much to slow it down so keep an eye on the radar in case you want to park your car undercover IMO.

Yeah, that last paragraph is especially pertinent in setups like these (with increasing broadscale destabilisation ahead of approaching big upper systems) because it takes a lot of widespread and persistent thick cloud cover/precip/early storms to continue well into the afternoon in order for it to shut down all action for later in the day.
Only takes some clearer gaps to open up at some stage during the day for an extra helping hand and bang, things can fire up easily. The strong dynamics with these setups do the rest of the heavy lifting. And especially if strong steering winds aloft can advect inland activity to the coast.

In saying that, I haven’t had a look at things specifically for Sydney yet so I’m not certain yet what later today will be like there.
 

Billy Bob

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Nov 23, 2020
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Could be a red letter day in Sydney (or a red echo day) if there is enough heating. A severe storm hit Royalla in the early hours of the morning, around 30 mm in quick time and some hail. Lots of red echoes on the Canberra radar early this morning.

Also a brief hailstorm around Yetholme this morning.

Moar storms are forecast this afternoon, though we currently have some Larry Leftover rain periods (old storms) which will inhibit Mr. Con Vection for a while.
 
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