End of week bitterly cold outbreak
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- TonyT
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End of week bitterly cold outbreak
The cold outbreak forecast for the end of this week (mostly friday for the South Island, Saturday for the north) is one of the coldest I have ever seen predicted by the models in my nearly 20 years of forecasting. For the last two days the US models are suggesting thicknesses of 516 over the South Island fro Friday and 520 over the North Island for Saturday, which are probably sufficient to bring snow to sea level including much of the North Island. I cant recall seeing predicted thickness values this low over the country before.
What will probably happen between now and then is that the model will make the prediction a little less cold, but even so be prepared for snow to low levels over much of the country at the end of the week. Fortunately falls should be light with the cold air being relatively dry.
What will probably happen between now and then is that the model will make the prediction a little less cold, but even so be prepared for snow to low levels over much of the country at the end of the week. Fortunately falls should be light with the cold air being relatively dry.
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I remember snow being forecast to sea-level for the south and east of the North Island in long-range forecasts back at the beginning of July 1994. About a day before the predicted outbreak the coldness of the forecast was toned back, though an icy blast did occur - snowfall levels only got to near sea-level briefly in the Wairarapa and Wainuiomata, and were above about 200-400 metres further north in the east of the North Island. The southerly of mid July 1995 was probably the coldest in recent years, with snow showers to sea-level briefly in Wellington, and to about 100 metres I think around Gisborne.
Ben
Christchurch
Ben
Christchurch
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I've been staring at the NOGAPS and AVN models in the last few days and again tonight. As an emergency manager have spent most of the day sorting out the chains and general preparedness of the ambulance service down here today. It is nice to have the abliity to plan a couple of days ahead of potential significant weather systems. Temp was 4 degrees at 6pm tonight and falling and so is the pressure .A slight downward drift.No rain since mid afternoon.You know there is more to come.
Cheers
Chris
Cheers
Chris
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Yeap the maps for Thursday Friday look very cold.
Saturday Sunday and Monday could see the coldest minimums for the winter set as that southerly clears.
Must places had a couple of good frosts before this system arrived, these happened with little snow on the mountains.
As this southerly clears there will be a lot more snow thus some inland areas will see some very serve frosts. I wouldn’t be surprise if temps drop to below –15 in inland Otago and Canterbury.
Alexandra may see some hoar frost as we often get a lot of fog after it rains or snows in winter.
Saturday Sunday and Monday could see the coldest minimums for the winter set as that southerly clears.
Must places had a couple of good frosts before this system arrived, these happened with little snow on the mountains.
As this southerly clears there will be a lot more snow thus some inland areas will see some very serve frosts. I wouldn’t be surprise if temps drop to below –15 in inland Otago and Canterbury.
Alexandra may see some hoar frost as we often get a lot of fog after it rains or snows in winter.
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The icy blast is still on track for Friday and Saturday, with models suggesting the 528 thickness line crossing the far north by late Saturday. Not as extreme as the earlier model(s) that Tony saw on Monday, but still bitterly cold. The latest MetService long-range forecast now has snow to low-levels on Friday, and very low levels on Saturday - for the North Island!
What a change from the warmest June on record.
Ben
Christchurch
What a change from the warmest June on record.
Ben
Christchurch
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June temperature was onlu 0.9oC warmer than normal here (my readings) ...i.e we didnt get the fohn NW effect eastern areas of NZ did, and instead had cloudy non sunnry days!
we have had snow falling briefly on the coastal (500 feet high) hills here before,.....i wonder if it will happen again,,,especialy as the flow looks to be SSE...which will mean the showers will move over land to get to auckland, up throughthe king country/taranaki, and wont warm up over the tasman sea, and so we just might be snow to low levels up this way!
we have had snow falling briefly on the coastal (500 feet high) hills here before,.....i wonder if it will happen again,,,especialy as the flow looks to be SSE...which will mean the showers will move over land to get to auckland, up throughthe king country/taranaki, and wont warm up over the tasman sea, and so we just might be snow to low levels up this way!
- TonyT
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Actually it is still as extreme - latest GFS is giving 517 over Chch Friday night/Saturday with 850 temps down to -8. Still looking for 520 over southeast of the NI, and under 524 (the usual indicator of snow to low levels) for much of the Island.
Interestingly the model wants to bring more moisture in on Friday night and Saturday now, with a small depression possibly developing to the east. This is going to be quite a ride , probably not heavy snow, but cold enough for falls to be widespread in most populated areas of the country, and some really extreme frosts to follow.
Interestingly the model wants to bring more moisture in on Friday night and Saturday now, with a small depression possibly developing to the east. This is going to be quite a ride , probably not heavy snow, but cold enough for falls to be widespread in most populated areas of the country, and some really extreme frosts to follow.
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MetService has revived an old phrase, made (in)famous by Saddam Hussein and Ruth Richardson back in'91. The latest special weather advisory talks of 'the mother of all polar southerly outbreaks' Now when MetService starts talking like that, it must be serious, even if this bulletin is only referring to Otago and Southland at this stage.
I don't think we've had a full-on winter polar southerly blast over all of NZ since the mid 90s. Sure there have been some severe snowstorms, but they've tended to be localised events, such as Canterbury's big snow in June last year. All the polar style (ie with air coming fron near Antarctica) southerlies of recent years seem to occurred out of season, like November 2000 and January 1998.
I don't think we've had a full-on winter polar southerly blast over all of NZ since the mid 90s. Sure there have been some severe snowstorms, but they've tended to be localised events, such as Canterbury's big snow in June last year. All the polar style (ie with air coming fron near Antarctica) southerlies of recent years seem to occurred out of season, like November 2000 and January 1998.
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New Depression in the north
There is a depression on the map moving SE from Australia-it must be one that will be captured in the surface westerlies as the wind here(SW) hasnt abated yet and it should be dropping the wind by now as Norfolk Is has easterlies now of 47 knots(our forecast is light winds going S with rain)
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Interesting reading from the metservice
For those that have not seen it yet..
Severe Weather Outlook
Valid: Fri 04 July to Mon 07 July
Issued: Wed 02 July 2003 at 01:44 pm
A wintry southerly outbreak is expected to spread over the whole country during Friday and Saturday, bringing snow to low levels, mainly in the east of both islands. Some heavy falls of snow are possible about Southland, including the Catlins, and also about the Desert Road. The flow should tend southwest during the weekend, with the shower activity easing.
On Monday, a ridge is likely to spread over the country, bringing settled but frosty weather.
Special Weather Advisory
And this one its a bit long
http://www.metservice.co.nz/forecasts/swa.asp
Oh good to see the polar blast is still on it's way
[/img]
For those that have not seen it yet..
Severe Weather Outlook
Valid: Fri 04 July to Mon 07 July
Issued: Wed 02 July 2003 at 01:44 pm
A wintry southerly outbreak is expected to spread over the whole country during Friday and Saturday, bringing snow to low levels, mainly in the east of both islands. Some heavy falls of snow are possible about Southland, including the Catlins, and also about the Desert Road. The flow should tend southwest during the weekend, with the shower activity easing.
On Monday, a ridge is likely to spread over the country, bringing settled but frosty weather.
Special Weather Advisory
And this one its a bit long
http://www.metservice.co.nz/forecasts/swa.asp
Oh good to see the polar blast is still on it's way
[/img]
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Norfolk Island Airport, Australia (YSNF) 29-02S 167-56E 109M
Jul 02, 2003 - 12:00 AM EDT / 2003.07.02 0400 UTC
Wind: from the E (100 degrees) at 9 MPH (8 KT):0
Visibility: greater than 7 mile(s):0
Sky conditions: mostly cloudy
Temperature: 64 F (18 C)
Dew Point: 55 F (13 C)
Relative Humidity: 72%
Pressure (altimeter): 30.00 in. Hg (1016 hPa)
ob: YSNF 020400Z 10008KT 9999 FEW022 SCT120 BKN210 18/13 Q1016
cycle: 4
easterly of 8 knots
Jul 02, 2003 - 12:00 AM EDT / 2003.07.02 0400 UTC
Wind: from the E (100 degrees) at 9 MPH (8 KT):0
Visibility: greater than 7 mile(s):0
Sky conditions: mostly cloudy
Temperature: 64 F (18 C)
Dew Point: 55 F (13 C)
Relative Humidity: 72%
Pressure (altimeter): 30.00 in. Hg (1016 hPa)
ob: YSNF 020400Z 10008KT 9999 FEW022 SCT120 BKN210 18/13 Q1016
cycle: 4
easterly of 8 knots
- NZstorm
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Freezing levels will be on the rise by Saturday, so I see overnight Thursday/Friday being the most interesting period for this cold outbreak.
Hopefully the air is deeply unstable. In the last few years we have seen very cold outbreaks with shallow convection (under 3000m) and these tend to be busts. The shallow cb's tend to burn out easily over land.
Pity that low in the North Tasman is not tracking further south.
Hopefully the air is deeply unstable. In the last few years we have seen very cold outbreaks with shallow convection (under 3000m) and these tend to be busts. The shallow cb's tend to burn out easily over land.
Pity that low in the North Tasman is not tracking further south.
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There is an area in the east of the South Island that tends to get a lot less snow to low levels from very cold southerly outbreaks than places further to the south and and the north. This area is covers most of the land between Dunedin and inland mid-Canterbury. Relatives of mine who live near Palmerston, between Oamaru and Dunedin, say that when Dunedin is having snow, they're usually getting fine weather instead. Why? This whole area (including North Otago and South Canterbruy) is exposed to the south, but maybe it's because there are no significant high hills right by the coast, like there are near Dunedin and Christchurch.
Ben
Christchurch
Ben
Christchurch
- TonyT
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Dont expect heavy snows out of this event - air this cold can only hold relatively little moisture, so there's not much to precipitate out. Steven might check the total precitable water stats for McQuarie Island tomorrow, and Invercargill on Friday and tell us how much is there.
Almost all heavy snow events in NZ originate from warm advection storms where warmer air looses its moisture above a very cold surface layer. This is not expected to be one of these storms, its a cold advection jobbie, and consequently the moisture content will be low. GFS is predicting about 8-9mm of rain over about 36 hours for Chch, which could easily translate to 8-9cm of snow given the temperatures. Certainly enough to bring the city to a standstill, but hardly in the heavy category. You might expect twice that depth on the hill country with some orographic lifting.
Note well though that if this cold air gets far enough north to interact with the depression(s) which the models want to bring across the north of the NI then warm advection snow is a possibility for the NI high country (and maybe low country as well).
Almost all heavy snow events in NZ originate from warm advection storms where warmer air looses its moisture above a very cold surface layer. This is not expected to be one of these storms, its a cold advection jobbie, and consequently the moisture content will be low. GFS is predicting about 8-9mm of rain over about 36 hours for Chch, which could easily translate to 8-9cm of snow given the temperatures. Certainly enough to bring the city to a standstill, but hardly in the heavy category. You might expect twice that depth on the hill country with some orographic lifting.
Note well though that if this cold air gets far enough north to interact with the depression(s) which the models want to bring across the north of the NI then warm advection snow is a possibility for the NI high country (and maybe low country as well).
- TonyT
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Interesting observation.tich wrote:There is an area in the east of the South Island that tends to get a lot less snow to low levels from very cold southerly outbreaks than places further to the south and and the north. This area is covers most of the land between Dunedin and inland mid-Canterbury. Relatives of mine who live near Palmerston, between Oamaru and Dunedin, say that when Dunedin is having snow, they're usually getting fine weather instead. Why? This whole area (including North Otago and South Canterbruy) is exposed to the south, but maybe it's because there are no significant high hills right by the coast, like there are near Dunedin and Christchurch.
Ben
Christchurch
Most (but not all) snow events for South Otago up to Dunedin are in southwest flow. They certainly get snow from southerly or southeasterly flow too, but these are just less frequent than sou'westers. The trajectory of cyclonically curving southwesterlies pushes the showers out to sea around or just north of Dunedin and brings the well known "fizzers" to North Otago and Canterbury.
Now almost all cold events which put snow on the Canterbury Plains (as opposed to the hill country) are in southerly or southeasterly flow, very rarely if at all in southwest flow. The south and southeast flows are usually anticyclonically curving around a ridge which is in the process of forming over the far south. Hence they miss North Otago/ South Canty too because of the curvature of the flow.
I think the best chances for snow in that North Otago/South Canty region are in true southeast tending easterly flow, ie when a depression is moving across the North Island.
I'm not sure if this really explains it, but perhaps its a step in the right direction.
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Warm advection snowstorms tend to affect inland areas like Central Otago and the Mackenzie Basin, rather than coastal places. June 2002's big snow in Canterbury was an exception - but even that one missed most of Banks Peninsula, while blanketing much of the plains.Almost all heavy snow events in NZ originate from warm advection storms where warmer air looses its moisture above a very cold surface layer. This is not expected to be one of these storms, its a cold advection jobbie, and consequently the moisture content will be low. GFS is predicting about 8-9mm of rain over about 36 hours for Chch, which could easily translate to 8-9cm of snow given the temperatures. Certainly enough to bring the city to a standstill, but hardly in the heavy category. You might expect twice that depth on the hill country with some orographic lifting.
I've wondered about that possibilty. The models seem to push the depression off to the east before the coldest air arrives up north, but if the 2 systems happen to collide - the scenario could be almost unimagineable. Civil Defence should be aware of this possibility. Low-lying towns and cities in the North Island I don't think could easily cope with a major snowfall event like the ones that periodically hit places like Dunedin from time to time.Note well though that if this cold air gets far enough north to interact with the depression(s) which the models want to bring across the north of the NI then warm advection snow is a possibility for the NI high country (and maybe low country as well).
Ben
Christchurch
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Both of the heavy snow events in Canterbury in 1992 were warm advection storms (yes Aaron, there were 2 that winter, you probably only remember the one which put snow in Chch, but there was one a few weeks earlier which put heavy snow down to about 300m from memory).tich wrote:
Warm advection snowstorms tend to affect inland areas like Central Otago and the Mackenzie Basin, rather than coastal places. June 2002's big snow in Canterbury was an exception - but even that one missed most of Banks Peninsula, while blanketing much of the plains.
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Cheers Tony and Tich.
I remember back in the early to mid nineties cold snap after cold snap were forecast to hit Canterbury only for them to head out to sea at the Otago Peninsula and start flowing inland again from Banks Peninsula northwards,an explanation from someone at Metservice at the time on local radio was that the Nth Otago/Mid Canterbury were sheltered from the Southern Alps?.But looking back they must have been more southwesterly flows,as Tony explained.
Looking at the maps/charts tonight,a more southerly direction on Friday should see this one being more widespread. ,especially with no high forming to the south of the country until at least Saturday.
Cheers.
I remember back in the early to mid nineties cold snap after cold snap were forecast to hit Canterbury only for them to head out to sea at the Otago Peninsula and start flowing inland again from Banks Peninsula northwards,an explanation from someone at Metservice at the time on local radio was that the Nth Otago/Mid Canterbury were sheltered from the Southern Alps?.But looking back they must have been more southwesterly flows,as Tony explained.
Looking at the maps/charts tonight,a more southerly direction on Friday should see this one being more widespread. ,especially with no high forming to the south of the country until at least Saturday.
Cheers.