Complex low pressure system & cold outbreak 3rd-8th August

[Bradley]

Yeah she kinda puts this system into perspective but hey, it's still 10 times better then any system we've had this winter so far!![/quote]
She states it is an unusual event.. it looks to be better than anything we have had for at least 2 years![/quote]

By 'we' you mean Christchurch because only last June they had 30cm down to 200m in places like Darfield...

[snowchaser01]

I mean it looks be the first time for a year or 2 that snow will settle to sea level.. 50/50 at this stage mind you.

[snowchaser01]

For future reference...

SEVERE WEATHER WARNING.

ISSUED BY MetService AT 8:47 pm 02-Aug-2016
Heavy snow for inland parts of Southland, Otago during Wednesday, and South Canterbury during Wednesday and Thursday
A complex low pressure system is expected to move onto the country from the south Tasman Sea during Wednesday, then move slowly northeastwards across New Zealand during Thursday and Friday, bringing rain to many parts of the country, with snow lowering to low levels about the east of the South Island.

The heaviest snow is likely about inland parts of Southland, Otago during Wednesday, where 20 to 30cm of snow is expected above 400m. For South Canterbury south of Fairlie, heavy snow is likely during Wednesday and early Thursday, with 25 to 35cm expected above 400 metres.

Heavy snow can cause major distruption to transport as well as significant stress to livestock, and could cause power disruption. Blizzard conditions are also likely in exposed areas.

Note, further snow is likely in eastern Otago early on Thursday, and from Canterbury to Kaikoura Coast during Thursday and Friday, and possibly to near sea level.

HEAVY SNOW WARNING
AREA/S AFFECTED
Inland parts of Southland and Clutha.
FORECAST
Rain is expected to turn to snow above 200 metres Wednesday morning. In the 12 hours from 6am to 6pm Wednesday, expect 15 to 25cm to accumulate above 400 metres, with 5 to 10cm possible down to 200 metres.

FREEZING LEVEL: Lowering to 600 metres late Wednesday afternoon.

AREA/S AFFECTED
Otago, except for Clutha
FORECAST
Rain is expected to turn to snow above 200 metres Wednesday morning. In the 18 hours from 6am to midnight Wednesday, expect 20 to 30cm to accumulate above 400 metres, with 5 to 10cm down to 200 metres. Heavy snow is expected to ease about Central Otago and Southern Lakes late Wednesday afternoon or evening, but continue in eastern Otago through to midnight Wednesday.

Note, a Watch is in place for heavy snow to 400 metres in eastern Otago Thursday morning

AREA/S AFFECTED
Inland parts of South Canterbury south of Fairlie, including the Mackenzie Basin.
FORECAST
Rain is expected to turn to snow above 200 metres Wednesday morning. In the 24 hours from 9am Wednesday to 9am Thursday, expect 25 to 35cm to accumulate above 400 metres, with 10 to 15cm down to 200 metres.

Note, a Watch is in place for possible heavy snow to low levels for Canterbury during Thursday and Friday.

FREEZING LEVEL: Lowering to 600 metres Wednesday morning.

NEXT SEVERE WEATHER WARNING WILL BE ISSUED AT OR BEFORE 9:00 am Wednesday 03-Aug-2016


Severe Weather Watch
Valid to 8:54pm Wednesday 3 Aug 2016

SEVERE WEATHER WATCH FOR TARARUA, KAPITI HOROWHENUA, WELLINGTON,WAIRARAPA, BULLER, CHRISTCHURCH, CANTERBURY PLAINS, NORTH OTAGO,DUNEDIN ISSUED BY METSERVICE AT 2054hrs 02-Aug-2016

BURST OF HEAVY RAIN FOR BULLER AND TARARUA RANGE, and EASTERN OTAGO WEDNESDAY. HEAVY SNOW ABOUT EASTERN PARTS OF THE SOUTH ISLAND THURSDAY AND FRIDAY.

A complex low pressure system is expected to move onto the country from the south Tasman Sea during Wednesday, then move slowly northeastwards across New Zealand during Thursday and Friday,bringing rain to many parts of the country, with snow lowering to low levels about the east of the South Island. A Warning for Heavy Snow is in place for inland parts of Southland, Otago and inland South Canterbury south of Fairlie.

This Watch is for the possibility of rainfall accumulations reaching short-duration warning amounts (eg. 50mm in 6 hours, or 70mm in 12 hours) in the ranges of BULLER and the TARARUA RANGE during Wednesday morning and afternoon.

This Watch is also for the possibility of rainfall accumulations reaching warning criteria (40mm in 12 hours) about eastern Otago north of Dunedin during Wednesday from mid-morning to early evening.

Additionally, this Watch is for the possibility that further significant snow is possible about DUNEDIN and NORTH OTAGO Thursday morning, and that snow accumulations could approach warning amounts to low levels in CANTERBURY and the KAIKOURA COAST and RANGES on Thursday and Friday.

People in all these areas should keep up to date with the latest forecasts, as parts of this Watch may be upgraded to a full warning, and further areas could be added.

This Watch will be reviewed by 10am Wednesday 3 August 2016

[tich]

Latest EC run is much the same as this mornings, around 10-12mm of rain for the total event (wed-sat) for Christchurch and perhaps 1-2cm of snow on Friday whereas inland area like Sheffield at 300m asl is showing around 15-20cm, certainly going to be almost exclusively an inland event this one!

How much Chch gets probably depends on whether the flow in southerly or southeasterly - Banks Peninsula shelters us somewhat in the latter airflow.

[snowchaser01]

Latest EC run is much the same as this mornings, around 10-12mm of rain for the total event (wed-sat) for Christchurch and perhaps 1-2cm of snow on Friday whereas inland area like Sheffield at 300m asl is showing around 15-20cm, certainly going to be almost exclusively an inland event this one!

How much Chch gets probably depends on whether the flow in southerly or southeasterly - Banks Peninsula shelters us somewhat in the latter airflow.

100% agree, in saying that though, if there is enough moisture sometimes the sheltering doesn't take place. I've seen that happen plenty of times.

[Razor]

Yes the metservice rain map certainly displays the Banks Peninsula sheltering effect for Friday night

[mikestormchaser]

heres a graph from the GFS metrogram, the 500mb THK totals are sitting around the 525 mark, but theres a long duration of time that the 850mb sits on -7C meanwhile there still is alot of moisture being ploted over this duration of time.
Iv added the CAPE into it to give any indications of convection enhancing any chance of heavy showers witch of course would drag the freezing level down but its only plotting around 100 CAPE.
Not that this event is relying on convection really, just thought id add it in.

[snowchaser01]

heres a graph from the GFS metrogram, the 500mb THK totals are sitting around the 525 mark, but theres a long duration of time that the 850mb sits on -7C meanwhile there still is alot of moisture being ploted over this duration of time.
Iv added the CAPE into it to give any indications of convection enhancing any chance of heavy showers witch of course would drag the freezing level down but its only plotting around 100 CAPE.
Not that this event is relying on convection really, just thought id add it in.

Wouldn't worry too much about thk levels. They don't matter as much when it comes to advection events.

[mikestormchaser]

heres a graph from the GFS metrogram, the 500mb THK totals are sitting around the 525 mark, but theres a long duration of time that the 850mb sits on -7C meanwhile there still is alot of moisture being ploted over this duration of time.
Iv added the CAPE into it to give any indications of convection enhancing any chance of heavy showers witch of course would drag the freezing level down but its only plotting around 100 CAPE.
Not that this event is relying on convection really, just thought id add it in.

Wouldn't worry too much about thk levels. They don't matter as much when it comes to advection events.

Not for tomorrow /Thursday but fri I wouldn't be calling it advective? Looks warm advective tomorrow but come fri cold advective. It's a hard one to call this event, I'm sitting on the fence but also have a little suspicion about it

[snowchaser01]

I have had a sneaky suspicion for a while that something isn't showing up...you know that gut feel. I guess its a waiting game

[snowykiwi]

I've woken up to light rain falling here in Rakaia (5.30am) Will keep you posted during this event on the weather here and in Methven where I work. Waiting with interest to see how this weather system unfolds. One of the older Methven residents I was speaking to this week clearly remembers the big snow of 4th August 1972 when Methven received 4 feet of snow.

[snowykiwi]

I now see the Metservice have snow for Rakaia on Monday, is there another system coming up the rear of this latest one?

[NZstorm]

I now see the Metservice have snow for Rakaia on Monday, is there another system coming up the rear of this latest one?

Gfs shows warm advective snow from a Tasman low on Tuesday. But a long away out for the modelling.

GFS has some major winter weather over lower North Island Saturday. Not sure it will verify but the 500mb polar jet is looking intense for the North Island on Saturday.

[Richard]

CHCH More FM at 6.00am had a ridiculous news item where it was said it was going to be very cold over the next few days, but it wont be as cold as in 1903 when -25.6 was recorded, and said Timaru had -9deg. Completely different weather system setup

[Bradley]

I see GFS has had a big downgrade in regards to moisture for Christchurch with only around 20mm for the event now, also a further downgrade with EC only going for 11mm for Christchurch now all up

[RWood]

I've woken up to light rain falling here in Rakaia (5.30am) Will keep you posted during this event on the weather here and in Methven where I work. Waiting with interest to see how this weather system unfolds. One of the older Methven residents I was speaking to this week clearly remembers the big snow of 4th August 1972 when Methven received 4 feet of snow.

The big snow event was in 1973 ...

[Bradley]

I've woken up to light rain falling here in Rakaia (5.30am) Will keep you posted during this event on the weather here and in Methven where I work. Waiting with interest to see how this weather system unfolds. One of the older Methven residents I was speaking to this week clearly remembers the big snow of 4th August 1972 when Methven received 4 feet of snow.

The big snow event was in 1973 ...

Also NIWA quotes in their Canterbury Snow Storm report below that Methven had 61cm in 73' - not 4 feet

https://www.niwa.co.nz/sites/niwa.co.nz ... e_2006.pdf

[snowchaser01]

Remember, bigger picture! It does seem as if moisture levels have backed off a tad, but its SE and models sometimes don't picking up the banking. I agree though, touch and go for the sheltering aspect for Christchurch.

[mikestormchaser]

Can certainly see the sheltering affect now for the city. But still a reasonable amount on the 6pm run of gfs.

[TonyT]

The depression is going to be too pasty and anemic as it crosses the North Island to do much. The action weather is happening off the coast now as the low spins up. By the time it gets into a position to bring something interesting onto Canterbury it will have weakened, and then moves away further. We will be left with the cold airflow but not much else. The stars haven't quite aligned for this one.

[Razor]

The depression is going to be too pasty and anaemic as it crosses the North Island to do much. The action weather is happening off the coast now as the low spins up. By the time it gets into a position to bring something interesting onto Canterbury it will have weakened, and then moves away further. We will be left with the cold airflow but not much else. The stars haven't quite aligned for this one.

Spies tell me Haast Pass is closed by snow and it seems some lowish falls starting to occur ie Mt Cook Village, Glenorchy to name a couple

[Bradley]

Well the model that always does the best in these scenarios has been quite consistent the last 24-36 hours with a big downgrade for this system, it's only that certain people have been looking at the least reliable model, GFS, and going with it's data that this has been hyped up!

[Manukau heads obs]

the front is moving quickly ahead of the low off Foirdland , onto westland
and will encourage a new replacement low center to form east of the alps once it cross over
and
as that happens,i.e as the barometer drops, you will get the warm advection setup

so, keep an eye on your barometer , people in Canterbury

why right it off before it has even started?

[Growler]

Taken from FB, not my image.

Mt Cook Village approx 9:45am this morning.

[Razor]

Briefly Sunshine now in ChCh, scattered light showers around to the west and south. looks to be a reasonably substantial rain band feeding through South Canterbury, as predicted by MS