Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Razor · Unread post by **Razor** » Fri 29/07/2022 10:25

MS has issued a couple of warnings for a possible impact from a system that Tony has very astutely been talking about in recent days

Heavy rain for central New Zealand. Heavy snow for the upper South Island.

A low pressure system is expected to move across the upper South Island late Saturday and Sunday morning, bringing a period of heavy northerly rain followed by cold southerly rain. The heaviest falls are expected in Nelson, Marlborough and Wellington, where accumulations may approach warning criteria. A period of snow is likely about inland parts of Marlborough and North Canterbury, with a Watch in force for heavy snow above 400 metres.

Note, there is some uncertainty with the track of this low, and people are advised to keep up to date with the latest forecasts in case further areas are added, or upgraded to a Warning.

Heavy Rain Watch

Area: Nelson

Period: 11hrs from 1pm Sat, 30 Jul - midnight Sat, 30 Jul

Forecast: A period of heavy northerly rain, rainfall accumulations may approach warning criteria

Area: Marlborough

Period: 17hrs from 2pm Sat, 30 Jul - 7am Sun, 31 Jul

Forecast: A period of heavy northerly rain turning southerly overnight Saturday. Rainfall accumulations may approach warning criteria. Note, rain may fall as snow to about 200 metres south of Seddon from Saturday night as detailed in the Heavy Snow Watch.

Area: Wellington

Period: 18hrs from 2pm Sat, 30 Jul - 8am Sun, 31 Jul

Forecast: Periods of heavy rain. Rainfall accumulations may approach warning amounts.

Heavy Snow Watch

Area: Inland Marlborough south of Seddon, and Canterbury High Country north of Culverden

Period: 10hrs from 8pm Sat, 30 Jul - 6am Sun, 31 Jul

Forecast: A period of heavy snow above 400 metres, with lighter falls down to about 200 metres. Snow accumulation above 400 metres may approach warning criteria.

Issued: 9:37am Fri, 29 Jul
Next update: 9pm Fri, 29 Jul

Razor · Unread post by **Razor** » Fri 29/07/2022 10:29

MS also quite bullish in the modelled amounts for ChCH tomorrow evening, punting for 30mm+ in the 8 hours from 5pm. That would cause more issues after the month thats been for sure- but to me that seems on the high side?

Bradley · Unread post by **Bradley** » Fri 29/07/2022 11:05

Both the GFS and EC deterministic and ensemble models are all predicting between 7-15mm on Saturday night so 30mm does seem on the high side that's for sure...

Razor · Unread post by **Razor** » Fri 29/07/2022 11:43

Bradley wrote: Fri 29/07/2022 11:05 Both the GFS and EC deterministic and ensemble models are all predicting between 7-15mm on Saturday night so 30mm does seem on the high side that's for sure...

Latest GFS run has dragged the system a bit further south which is of interest

spwill · Unread post by **spwill** » Fri 29/07/2022 11:50

Some risk for thunderstorms/hail showing for the west of the North Island Sunday morning, the risk is mostly south of Auckland but see how the upper trough tracks in next model runs.

TonyT · Unread post by **TonyT** » Fri 29/07/2022 12:43

Bradley wrote: Fri 29/07/2022 11:05 Both the GFS and EC deterministic and ensemble models are all predicting between 7-15mm on Saturday night so 30mm does seem on the high side that's for sure...

Looking at the latest guidance, for Chch to midday Sunday GFS is at 30mm, EC, Access, icon 11-16mm, UKMO 9mm.

Razor · Unread post by **Razor** » Fri 29/07/2022 12:50

TonyT wrote: Fri 29/07/2022 12:43
Bradley wrote: Fri 29/07/2022 11:05 Both the GFS and EC deterministic and ensemble models are all predicting between 7-15mm on Saturday night so 30mm does seem on the high side that's for sure...
Looking at the latest guidance, for Chch to midday Sunday GFS is at 30mm, EC, Access, icon 11-16mm, UKMO 9mm.

Meanwhile MS has now dialled back to 10mm. Obviously a bit of uncertainly on the edges.

mikestormchaser · Unread post by **mikestormchaser** » Fri 29/07/2022 16:14

The low pressure system is dragging it further south on latest guidance. Will be some heavy snow down to low levels tomorrow night/ Sunday.

Awhituobs · Unread post by **Awhituobs** » Fri 29/07/2022 21:26

is this low #9 from the tasman for the month of July?

TonyT · Unread post by **TonyT** » Fri 29/07/2022 21:38

Predicted Christchurch precip totals to midday Sunday from the operationals - UKMO 27mm, GFS 21mm, EC 19mm, Access 16mm, Icon 15mm

Razor · Unread post by **Razor** » Sat 30/07/2022 07:55

Looks like those numbers have ramped up a bit too. Could be problematic in Chch tonight. Nasty little system for the farmers further afield too

Cantab03 · Unread post by **Cantab03** » Sat 30/07/2022 08:17

Razor wrote: Sat 30/07/2022 07:55 Looks like those numbers have ramped up a bit too. Could be problematic in Chch tonight. Nasty little system for the farmers further afield too

Yes metservice putting out 42mm for CHCH by midnight now on projection.

Bradley · Unread post by **Bradley** » Sat 30/07/2022 08:24

Latest EC ensemble data has 0.1cm of snow in Christchurch for this event although only 5 out of 50 members is predicting snow for Christchurch so not great odds..

Bradley · Unread post by **Bradley** » Sat 30/07/2022 09:51

Snow now forecast down to 100m for areas north of the Rangitata

Orion · Unread post by **Orion** » Sat 30/07/2022 13:46

The overcast has been descending all morning and the temperature quietly dropping over the past hour or so, currently 6.7°C and there may be a hint of precipitation in the air.

Razor · Unread post by **Razor** » Sat 30/07/2022 16:55

Very steady rain in Chch now. Was up port hills this arvo, there was rain to the north and rain to the south. Convergence zone material?

Orion · Unread post by **Orion** » Sat 30/07/2022 17:25

Rain has begun to patter on the roof here; wind SW; 5.6°C.

Razor · Unread post by **Razor** » Sat 30/07/2022 17:31

Heavy snow at friends place in Castle Hill

Richard · Unread post by **Richard** » Sat 30/07/2022 18:17

Sleet in the rain here now, 4deg.

Bradley · Unread post by **Bradley** » Sat 30/07/2022 20:41

Cold air not penetrating at all here in West Melton, been 4.5C for nearly 2 hours…

Razor · Unread post by **Razor** » Sat 30/07/2022 21:18

Same in town, 6 degrees for past 4 hours

Dean. · Unread post by **Dean.** » Sat 30/07/2022 21:23

3.7 degrees here at 109 metres in Ashburton...radar looking interesting offshore moving onshore

Dean. · Unread post by **Dean.** » Sat 30/07/2022 21:37

2 degrees in Methven at 320 metres close to snow there

Razor · Unread post by **Razor** » Sat 30/07/2022 21:55

Bit of a bouquet to Tony on calling this one well in advance of anyone else really. Tricky wee beast to spot and I note that MS just put an Orange Warning up at 8pm tonight.

13mm here so far and very steady falls indeed. Will be a few issues in Chch with this rate. Just dropped a degree to 5

Richard · Unread post by **Richard** » Sat 30/07/2022 22:37

Snowing here now and settling

NZ Weather Forum

Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

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Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July

Re: Developing Low Pressure - Upper South Island/ Lower North Island 30/31 July