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#1463357 - 07/05/2018 22:23 NSW Cold change and low with rain and snow- 11th & 12th May 2018
Wave Rider Offline
Meteorological Motor Mouth

Registered: 27/01/2014
Posts: 6778
I think it's time to kick this one off. It is pretty early but I am quite confident that there will be low level snow.

06z GFS still sticking with its guns in terms of cold with 850mb temps down to -3 at on Friday morning. Precip totals do look pretty slack tbh but should be enough orographic lift for snow on the higher parts exposed to the west. Orange may get some and Crookwell or at least the high ground to the SW will get snow as that is very exposed there. Warms up a little during the day but still below zero at 850mb, but not much moisture east of Bathurst so even Shooters Hill may struggle on Friday during the day. Sunny Corner will probably see light snow showers.

Friday night/Sat morning gets very interesting. The low forms off the NSW/VIC border, wrapping around cold air and quite a lot of precip. Most of it will be west and south of Bathurst but it penetrates possibly as east as the lower BM's so it looks like there will be heavy precip with 850mb temps still at 0 at 4am Saturday, but around Taralga area as low as -2. So my point here is that when the low forms, the air will mix pretty randomly so there could be a surprise low level fall if 900mb temps are really low for example, like 14th Oct 2014 in Lithgow and Blackheath. It warms up during the day with even more widespread precip covering the CT's by 4pm with 3-5mm and 850mb temps still around 0 to 1 so maybe some very marginal but heavy snow. Interestingly, unlike earlier runs, the airmass stays cool on Saturday night, but warms quickly on Sunday. So in fact there could almost be two full days of snow at some locations.

Meanwhile, ACCESS warms 850mb temps drastically from Saturday morning so would be no hope of snow during the day if that came off. So still not sure what exactly will happen but I think something close to the GFS situation will happen, I just have a feeling. But on the other hand I would not be surprised if it happened this way since it would just be my luck.

EC also in alignment with the other models in terms of cold 850mb temps on Friday. It is showing snow all day for the Oberon Plateau, but shouldn't be too heavy on Friday. It also continues all night and into Saturday morning where it could get a fair bit heavier before the warm air intrudes in the late morning. So it is in agreement with ACCESS, while GFS holds on to the cold temps through the day with heavy snow especially in the arvo.


Edited by Wave Rider (07/05/2018 22:25)
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The longer you wait for storms, the more you appreciate them.

2017-18 storm total= 11
Oct 25th
Nov 6th(3), 17th
Dec 2nd, 14th
Jan 2nd(2), 8th(2), 9th

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#1463358 - 07/05/2018 22:49 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Steve777 Offline
Weatherzone Addict

Registered: 20/10/2011
Posts: 4096
Loc: Artarmon (Sydney North Shore)
Good thread start WR, a lot of analysis in there.

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#1463359 - 07/05/2018 23:18 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Antarctic Whaler Offline
Cloud Gazer

Registered: 26/03/2018
Posts: 41
Loc: Black Springs NSW; 1,210 m AMS...
Splendid post as always, lad! smile grin I'll see what Black Springs & surrounds can offer wink

Let us hope for the best. Can't wait til this event initiates cheers bounce
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#1463370 - 08/05/2018 08:56 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Kino Offline
Weatherzone Addict

Registered: 10/08/2017
Posts: 2027
Loc: Wollongong, NSW, Aus
This event is pretty much looking dead in the water already, other than the highest peaks of the Snowies frown

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#1463372 - 08/05/2018 09:08 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Wave Rider Offline
Meteorological Motor Mouth

Registered: 27/01/2014
Posts: 6778
I would still bet on decent CT snow during Friday night and Saturday morning at this stage. Friday morning is coldest but not much moisture.
_________________________
The longer you wait for storms, the more you appreciate them.

2017-18 storm total= 11
Oct 25th
Nov 6th(3), 17th
Dec 2nd, 14th
Jan 2nd(2), 8th(2), 9th

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#1463389 - 08/05/2018 13:22 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Kino Offline
Weatherzone Addict

Registered: 10/08/2017
Posts: 2027
Loc: Wollongong, NSW, Aus
Hoping so WR - straws and everything crossed. If it happens, it's a significant cold event with temps in places the lowest this early since 1978!

Quote:
Widespread snow looms amid early-season cold snap
Ben Domensino, Tuesday May 8, 2018 - 12:30 EST
A pulse of Antarctic air will cause Australia's first widespread snowfall for 2018 at the end of this week.

A stray low pressure system venturing north from the Southern Ocean will cause temperatures to plummet across Australia's southeast in the coming days.

It is likely to get cold enough for snow to settle in Tasmania from Wednesday and in Victoria and NSW from Thursday. As the frigid air creeps further north during Friday and Saturday, snow could fall to low levels along the Great Dividing Range.

This system is likely to bring the first decent bout of snow for the year in Australia's alps. Models suggest that around 20-40cm of natural snow will accumulate in the alpine region between Thursday and Sunday.

Outside the alps, snow is forecast to reach down to 800-900 metres above sea level in central and western Victoria and over the Central Tablelands of NSW by Friday. Flakes may even fall over the Northern Tablelands of NSW if the cold air reaches far enough north during Friday night or Saturday morning.

While May snow is not uncommon in Australia, this is an unusually cold system for this early in the year.

Melbourne is forecast to reach highs of 13 degrees on Thursday and Friday, which would be the city's coldest pair of days this early in the season since 1978.

Canberra's forecast top of nine degrees on Friday would be the city's coldest day this early in the year since 1970.

Friday is also forecast to be the coldest day this early in the season for seven years at Thredbo (-3C), Cabramurra (0C), Ballarat (9C), Bendigo (12C) and Deniliquin (13C).

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#1463391 - 08/05/2018 13:43 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Kino]
petethemoskeet Offline
Weatherzone Addict

Registered: 13/08/2003
Posts: 1272
Loc: toowoomba
Kino why do you think it's dead in the water?Apart from ACCESS all the other models are still on it especially EC.

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#1463392 - 08/05/2018 13:49 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Kino Offline
Weatherzone Addict

Registered: 10/08/2017
Posts: 2027
Loc: Wollongong, NSW, Aus
Moisture....looks terrible at this stage (hoping PM runs will adjust nicely)**. It is sure going to be frigid but it will all depend on the low and it's wrap-around. No doubt the Oberon Plateau will see something, but for anything sub-1000m is unlikely at this stage - which means any snow chases for us east coastians is a min ~2.5 hours or more one way.

** terms and conditions apply

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#1463395 - 08/05/2018 16:40 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Homer Offline
Meteorological Motor Mouth

Registered: 16/06/2007
Posts: 5701
Loc: Dural
Thredbo TS in this afternoon's forecast going for 51 - 126 mm's - mostly snow.
This is an enormous system down south, especially for May.
Also Orange this afternoon has upgraded rain/snowfall totals up to 56 mm's. Much less snow though, but there will certainly be some.
At this stage.
This is May 2000-esque.


Edited by Homer (08/05/2018 16:47)

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#1463396 - 08/05/2018 16:43 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
DaveM Offline
Meteorological Motor Mouth

Registered: 21/05/2001
Posts: 10130
Loc: Bathurst NSW about 700 m asl
At least it's something a bit interesting grin

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#1463397 - 08/05/2018 16:46 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Homer Offline
Meteorological Motor Mouth

Registered: 16/06/2007
Posts: 5701
Loc: Dural
Lol at the forecast for Mt Buller in VIC for Saturday.

"-5 C to +2.
Heavy snowfalls possible.
Possible rainfall: 4 - 80 mm's"


4 - 80 mm's? lol. Hedging bets much?
Also, 2 - 40 mm's predicted for Sunday. Maybe a zero was left off the lower amounts, otherwise, that's quite crazy.

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#1463399 - 08/05/2018 17:39 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Sidney Offline
Weather Freak

Registered: 20/12/2013
Posts: 407
Loc: Macquarie fields ( South west ...
I guess the 4-80mm is based on where the low is positioned. If its too far west like how some runs were predicting then its more likely for it to be on the lower end of the scale. The prediction range should decrease as we get closer to the date.

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#1463401 - 08/05/2018 17:43 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Sidney]
Homer Offline
Meteorological Motor Mouth

Registered: 16/06/2007
Posts: 5701
Loc: Dural
Originally Posted By: Sidney
I guess the 4-80mm is based on where the low is positioned. If its too far west like how some runs were predicting then its more likely for it to be on the lower end of the scale. The prediction range should decrease as we get closer to the date.


Yes, I sorta agree, but don't the BOM base their forecast's on a particular model? I couldn't imagine any model predicting a range like that.
Just asking.

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#1463402 - 08/05/2018 18:02 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Homer]
Sidney Offline
Weather Freak

Registered: 20/12/2013
Posts: 407
Loc: Macquarie fields ( South west ...
Originally Posted By: Homer
Originally Posted By: Sidney
I guess the 4-80mm is based on where the low is positioned. If its too far west like how some runs were predicting then its more likely for it to be on the lower end of the scale. The prediction range should decrease as we get closer to the date.


Yes, I sorta agree, but don't the BOM base their forecast's on a particular model? I couldn't imagine any model predicting a range like that.
Just asking.


Yeah i agree never seen BoM base their forecast on multiple models. First time i've seen such a drastic range with rainfall prediction.

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#1463404 - 08/05/2018 18:20 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Jimi Offline
Weather Freak

Registered: 15/03/2004
Posts: 895
Loc: Cammeray
Itís not so much an expected range as a 50% chance of exceeding the lower limit and a 25% chance of exceeding the upper limit, isnít it? Thought of that way itís not too unreasonable (though I think thereís more than a 25% chance of the actual fall being between those numbers).

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#1463406 - 08/05/2018 18:44 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Jimi]
Steve777 Offline
Weatherzone Addict

Registered: 20/10/2011
Posts: 4096
Loc: Artarmon (Sydney North Shore)
That is correct. The following page from the BOM refers: BOM Glossary R

Quote:
"Rainfall, Likely rainfall

Likely rainfall is the amount with a 50% chance of occurring during the day. This element is displayed as a map on MetEye. It is also used as the lower value of the Possible Rainfall range in the Bureau's town forecasts.

Rainfall, Possible higher rainfall

Possible higher rainfall is the amount with a 25% chance of occurring during the day. Conversely, there is a 75% chance that this amount may not be reached. This element is displayed as a map on MetEye. It is also used as the higher value of the Possible Rainfall range in the Bureau's town forecasts.

Rainfall, Possible rainfall range

The possible rainfall amount is included on the Bureau's town forecasts, and describes the expected rainfall range for the day at that location. The rainfall range is a useful tool to highlight the variability of certain types of rainfall days. On showery/thunderstorm days, the possible rainfall range may be quite large (e.g. 5 to 30 mm). When steady rainfall is expected over a wide area, the range may be smaller (e.g. 10 to 15mm).

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#1463407 - 08/05/2018 18:45 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Jimi]
Homer Offline
Meteorological Motor Mouth

Registered: 16/06/2007
Posts: 5701
Loc: Dural
Originally Posted By: Jimi
Itís not so much an expected range as a 50% chance of exceeding the lower limit and a 25% chance of exceeding the upper limit, isnít it? Thought of that way itís not too unreasonable (though I think thereís more than a 25% chance of the actual fall being between those numbers).


I understand percentages are involved in all rain/snow forecasts. It just seems an obscene range. The percentage given in the forecast was "Very high - 95%".
Just seems odd (or lazy) to me.

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#1463413 - 08/05/2018 20:48 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Rob G Offline
Weather Freak

Registered: 31/07/2003
Posts: 703
Loc: Porters Retreat NSW
They've upgraded forecast rain totals for us on Friday and Saturday. Potentially up to 30mm. May fall as snow with a high of 3 deg C on Friday and 5 deg C on Saturday.

If the event comes off it will be the wettest two days in many months, and the first lower than normal daytime temperatures for I don't how long. Probably about due after endless warmth and dry.

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#1463417 - 08/05/2018 22:00 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
Kino Offline
Weatherzone Addict

Registered: 10/08/2017
Posts: 2027
Loc: Wollongong, NSW, Aus
You can see why they have hedged their bets - only EC is really gunning for this event now for the NSW Snowies, every other model keeps majority of the precip in Vict.

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#1463423 - 09/05/2018 07:26 Re: NSW Cold change and low with rain and snow- 11th & 12th May 2018 [Re: Wave Rider]
samboz Offline
Weatherzone Addict

Registered: 16/11/2014
Posts: 1975
Loc: Sale, NthGippsland, S/E VIC
With you on this Homer, my W.A.G. is that the nature of ECL forecasting is still very much based, as said, on where the L wanders/develops, and that ECL forecasting isn't pinned down in models yet.

But a range of 4 to 80, I reckon most folks could make a wild a++e guess like that and say they were 95% certain if would rain...lol
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