Rapid succession of fronts- Strong SW Flow (27 Oct-1st Nov)

Tornado Tim · Unread post by **Tornado Tim** » Mon 27/10/2014 21:27

Well we are moving into a very active weather pattern the rest of this week, with storms being a risk with the rapid secession of colds fronts moving through and then being dominated by a Strong SW flow.

The Polar orientated low will be dragging in some cold upper level temperatures with it later on this week.
Upper level temps will vary greatly later on as well, varying from -14 forecast for Cape Reinga to -32 in Invercargill on Friday.

Tornado Tim · Unread post by **Tornado Tim** » Mon 27/10/2014 21:38

Thunderstorm Outlook for reference:

MetService wrote:A front is expected to rapidly cross over the South Island and much of the North Island during Tuesday afternoon and evening. There is a general low risk that embedded thunderstorms will accompany the front as it passes over Westland and the northwest of the South Island in the afternoon and in the west of the North Island during the evening. There is now an added moderate risk of thunderstorms occurring over Auckland, Waikato, Taumarunui and northern Taranaki during the evening. These are likely to bring brief heavy rain in the 10-25mm/hr range and strong wind gusts.

Another front should be approaching Fiordland at night. There is a low risk of thunderstorms developing about the fiords at night. If the thunderstorms occur they are likely to be accompanied by localised heavy rainfall and strong wind gusts.

Elsewhere, no thunderstorms or significant convection expected.

03Stormchaser · Unread post by **03Stormchaser** » Mon 27/10/2014 23:19

We should see coastal storms on Wed in Canterbury

NZstorm · Unread post by **NZstorm** » Tue 28/10/2014 07:24

Yes, a big fluctuation in the airmasses.

Will watch for a possible storm on front tonight over Waikato/Auckland. Risk looks marginal. 850mb very moist though with dp11C at that level. A higher storm risk showing up over Northland tomorrow morning with very moist subtropical airmass.

That cluster of storms on the satellite out in the Tasman this morning look elevated. You can tell that by the speed they are moving.

spwill · Unread post by **spwill** » Tue 28/10/2014 11:54

The upper level pattern is looking more like early spring with the upper cold systems still coming quite far north.

On the humid side here now with the dewpoint at 17C, light rain.
Tomorrow night looks the best chance for thunder here with the cold trough crossing.

David · Unread post by **David** » Tue 28/10/2014 16:52

The dewpoint peaked at 18.6°C here today, though the max temp was only 20.2. Quite a humid day.

spwill · Unread post by **spwill** » Tue 28/10/2014 18:05

The front just west of here is looking more active now with some thunderstorm activity showing up

jamie · Unread post by **jamie** » Tue 28/10/2014 18:45

Sure was humid today. As I drove thru huntly the cloud base was below the red belt at the top of the chimney stacks. So I'm thinking about 100m high.

There were some hidden heavy showers about too. Radar didn't show them and nor could you see them from ground level. Must have been elevated.

spwill · Unread post by **spwill** » Tue 28/10/2014 18:49

Thunderstorm activity showing up near our west coast

Tornado Tim · Unread post by **Tornado Tim** » Tue 28/10/2014 18:58

Yup that front is fairly Lightning Active, will be cool if it stays that way.
Todays outlook for reference:

Metservice wrote: A front is expected to move rapidly across the South Island and much of the North Island from the west today. There is generally a low risk of thunderstorms associated with this front as it crosses Westland, Buller and Nelson this afternoon and the Marlborough Sounds, Kapiti and western areas of the North Island from Whanganui to central Northland including western Bay of Plenty and the Coromandel Peninsula this evening. However, for Taranaki,Taumarunui, western Taupo, Waitomo, Waikato and southern Auckland the risk of thunderstorms is moderate this evening and tonight. If thunderstorms occur they are likely to be accompanied by strong wind gusts and localised heavy rain with intensities of 10 to 20mm per hour.

A second front should be approaching the far south tonight. There is a low risk of thunderstorms developing about coastal Fiordland tonight, bringing localised heavy rainfall and strong wind gusts.

No other areas of severe convection or thunderstorms are expected.

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Overnight and the 29th October Morning:

Metservice wrote: Issued at: 10:55am Tuesday 28 Oct 2014

During Wednesday morning a slow-moving front should lie over Northland, Auckland and northern Waikato. There is a moderate risk of thunderstorms during the morning associated with this front for Northland and Auckland, and a low risk for the Coromandel Peninsula and northern Waikato. These thunderstorms may produce localised heavy rainfalls with intensities of 10 to 25mm per hour.

Another, very active, front is expected to move north over the South Island during the morning. There is a high risk of thunderstorms with and behind this front spreading north to affect Fiordland, Westland, Buller and western areas of Southland, Otago and Canterbury. These thunderstorms are likely to bring localised heavy rain with intensities of 15 to 25mm per hour and strong wind gusts of 90 to 110 km/h. There is a low risk that some of these thunderstorms may be severe and contain small tornadoes. In Fiordland there is also a high risk of hail of 5 to 15mm diameter and a low risk that hail of bigger than 20mm diameter could fall.

Outside of the high risk area, there is a low risk that some thunderstorms could spread further east into Nelson, Canterbury, Otago and Southland.

No other areas of thunderstorms or severe convection are expected.

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29th October PM Outlook (Nice, colourful and active):

Metservice wrote: A front over the north of the South Island at midday on Wednesday should move over the North Island during the afternoon and evening. Meanwhile, a trough following this front should cross the South Island. These features are expected to bring showers and possible thunderstorms to western areas of both islands.

The highest risk of thunderstorms is during the afternoon and evening in Buller and northwest Nelson. There is also a moderate risk of thunderstorms for Westland and Fiordland during the afternoon, for the Marlborough Sounds, Kapiti Coast, Manawatu, Wanganui and Taranaki during the afternoon and evening, and for Northland to the central North Island high country in the evening. These thunderstorms are likely to bring localised heavy rain with intensities of 10 to 20mm per hour and strong wind gusts of 90 to 110 km/h. Hail is also possible for the South Island areas and from Taranaki to Kapiti. There is a low risk that some of these thunderstorms could spread further east.

During the afternoon a southerly change is expected to move over Southland and Otago. There is a moderate risk that thunderstorms could develop on this change over Southland and eastern Otago (including Dunedin). If these thunderstorms occur they are likely to bring localised heavy rain with intensities of 10 to 20mm per hour and hail. As the change moves into Canterbury during the evening there is a low risk of thunderstorms along the Canterbury Plains.

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And the Lightning activity going on out to the west of us atm:

Tornado Tim · Unread post by **Tornado Tim** » Tue 28/10/2014 19:02

Owhh, some of those cells west of Auckland are breaching 60Dbz, nice

Tornado Tim · Unread post by **Tornado Tim** » Tue 28/10/2014 21:40

Usual for the front to loose its puff just before land......
Hopefully tomorrows chance is better....
I see you may have a slight chance of storm off the coast, Cantubury folk.... Models have a higher prob than MS.

Looks at the models at face value the Instability is fairly low with tomorrows setup over the North Island, however the upper level flow is very strong due to the sub Antartic jet inplace. Latent heat release by relative buoyant air by forcing should result in higher instability numbers than shown. I think this why I think Metservice has it at a Moderate Risk.

Also what else is very interesting the Jet is expected to Apex over Northland, strengthening the upper flow even more over the region.

This evenings outlook update from tonight to tomorrow morning:

Issued at: 8:50pm Tuesday 28 Oct 2014

During Wednesday morning a slow-moving front should lie over Northland, Auckland and northern Waikato. There is a moderate risk of thunderstorms during the morning associated with this front for Northland and Auckland, and a low risk for the Coromandel Peninsula and northern Waikato. These thunderstorms may produce localised heavy rainfalls with intensities of 10 to 25mm per hour. There is an additional low risk over Northland and northern Auckland of one or two localised downpours giving 25-35mm/hr and an outside risk of a small tornado.

Another, very active, front is expected to move north over the South Island during the morning. There is a high risk of thunderstorms with and behind this front spreading north to affect Fiordland, Westland, Buller and western areas of Southland, Otago and Canterbury. These thunderstorms are likely to bring localised heavy rain with intensities of 15 to 25mm per hour and strong wind gusts of 90 to 110 km/h. There is now a moderate risk that some of these thunderstorms may be SEVERE and produce wind gusts of 110+km/hr and the odd damaging tornado, mainly about the coast. In Fiordland there is also a high risk of hail of 5 to 15mm diameter.

Outside of the high risk area, there is a low risk that some thunderstorms could spread further east into Nelson, inland Marlborough, Canterbury, Otago and Southland.

No other areas of thunderstorms or severe convection are expected.

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Metservice wrote: A front over the north of the South Island at midday on Wednesday should move over the North Island during the afternoon and evening. Meanwhile, a trough following this front should cross the South Island. These features are expected to bring showers and thunderstorms to western areas of both islands.

The highest risk of thunderstorms is during the afternoon in Fiordland and Westland and during the afternoon and evening in Buller and northwest Nelson. There is also a moderate risk of thunderstorms for the Marlborough Sounds,Kapiti Coast, Manawatu, Wanganui and Taranaki during the afternoon and evening,and for Auckland to the central North Island high country in the evening. Over Northland the risk is low at night. These thunderstorms are likely to bring localised heavy rain with intensities of 10 to 20mm per hour and strong wind gusts of 90 to 110 km/h. Hail is also possible for the South Island areas and from Taranaki to Kapiti. There is a low risk that some of these thunderstorms could spread further east.

During the afternoon a southerly change is expected to move over Southland and Otago. There is a moderate risk that thunderstorms could develop on this change over Southland and eastern Otago (including Dunedin). If these thunderstorms occur they are likely to bring localised heavy rain with intensities of 10 to 20mm per hour and hail. As the change moves into Canterbury during the evening there is a low risk of thunderstorms over the Canterbury Plains.

No other areas of severe convection or thunderstorms are expected.

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NZstorm · Unread post by **NZstorm** » Tue 28/10/2014 22:04

We had a heavy shower in the last hour with about 8mm.

Looking forward to a dry day tomorrow but showers returning late.

Looks like a wind punch for the west for the North Island overnight Wednesday with 50knot squalls.

NZ Thunderstorm Soc · Tue 28/10/2014 22:07

-Calm and clear here at the moment, after a very windy ENE blowing across the city today, this probably resulting to a cold sea temperature offshore. ( I liked the cartoon in this morning's PRESS regarding if terrorists came to Christchurch)...
...sorry, the NW has just arrived.

.anyway, the cartoon has a reference to the infernal easterly wind.

NZstorm · Unread post by **NZstorm** » Wed 29/10/2014 05:57

Thunderstorms moving onto Northland this morning. And looks like that thundery front is coming further south than models were showing yesterday, Auckland may catch it.

Frequent lightning with it.

jamie · Unread post by **jamie** » Wed 29/10/2014 06:01

Nice blow up about to move over Northern Auckland

NZstorm · Unread post by **NZstorm** » Wed 29/10/2014 06:10

Rickys tracker has had over 800 strikes in the last 30minutes. But having another look at the radar, it will pass north of Auckland.

Manukau heads obs · Wed 29/10/2014 06:22

Blitzortung picking it up nicely

Manukau heads obs · Wed 29/10/2014 06:51

Thunder here

jamie · Unread post by **jamie** » Wed 29/10/2014 06:55

Northland radar helping out today. They have a severe thunderstorm warning on the northland radar on the top edge of the storm

NZstorm · Unread post by **NZstorm** » Wed 29/10/2014 07:03

I see Met Service say large hail. To get large hail there would need to be a supercell.

The convection has an elevated look to it.

Manukau heads obs · Wed 29/10/2014 07:07

Elevated CB just went over us
low cloud here...with no change to that got a burst
of heavy rain.a bit clearer now though behind it.
northland getting a good one alright
re hail..we might have a bit here

ricky · Unread post by **ricky** » Wed 29/10/2014 07:12

That is the most frequent lightning I've seen on the detectors for a long time!

NZstorm · Unread post by **NZstorm** » Wed 29/10/2014 07:18

Always get the best lightning off elevated storms. I had a listen to the am radio and spherics every second!

Tornado Tim · Unread post by **Tornado Tim** » Wed 29/10/2014 07:19

Nice amount of Lightning thats for sure, detector flashing frequently

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