Convective week 26-Nov to 4-Dec

[Razor]

And a Severe TS WATCH :
SEVERE THUNDERSTORM WATCH

Issued by MetService at 08:30 am Monday 27 November 2017
Valid until 08:30 pm Monday 27 November 2017
This watch affects people in the following weather forecast districts:
Taumarunui
Taupo
Hawkes Bay
Taranaki
Taihape
Wanganui
Manawatu
Tararua
Kapiti-Horowhenua
Wairarapa


Scattered heavy showers and thunderstorms are expected over inland parts of the central and lower North Island this afternoon and evening. For Taumarunui, Taupo, Taihape, inland parts of Taranaki, Whanganui Hill Country, Manawatu, Hawkes Bay and Wairarapa, there is a moderate risk that one or two of these thunderstorms could be SEVERE producing localised downpours of 25 to 40mm per hour, especially about the ranges. Rainfall of this intensity can cause flash flooding and may lead to slips and hazardous driving conditions.

Note: A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms in and close to the watch area. People in these areas should be on the lookout for threatening weather conditions and monitor for possible Severe Thunderstorm Warnings.


For information on preparing for and keeping safe during a storm, see the Civil Defence Get Ready Get Thru website

Issued by: Andy Downs

This watch will be updated by: 02:00 pm Monday 27 November 2017

[NZstorm]

Hard not to get excited with some of the GFS plots for this week

No wind shear though. But there is some bulk shear showing up on Friday/Saturday on GFS.

[treetopkk]

Some farmers in Central Otago talk of the"NE monsoon" Although absent in recent years the 90's had some good events lasting a week with temps around 30/33 high humidity and afternoon showers. This was a relief from the dry NW winds and dry cold winters . Recently we have not had blocking highs out east and deep moist NE flows. Off to a good start this year and its not December yet ! Bring it on

[Orion]

....Lots of flat cloud here this afternoon inland apart from some bubble-ups of Cu builds through that cloud around the Mt. Hutt area and up the Rangitata Gorge area.
Nothing much observed inland to look thunderstormic, except from about 3pm onward, you could see upper level Cb 'off cuts' if there is such a thing drifting east over the Timaru direction from here.
a more distinct Cb form drifted east later....

Very well described: the above is exactly what I observed while travelling south from Christchurch yesterday afternoon.
Specially those "upper level Cb 'off cuts' " which I could see and couldn't think what they might be called.

[tgsnoopy]

Recently we have not had blocking highs out east and deep moist NE flows. Off to a good start this year and its not December yet ! Bring it on

I might have to become more proactive with Waikato chases this summer in that case. Could be a good thing.

[Razor]

Watch now extended to upper inland South island. Radar certainly looks beefy the past hour or so

SEVERE THUNDERSTORM WATCH

Issued by MetService at 01:28 pm Monday 27 November 2017
Valid until 09:00 pm Monday 27 November 2017
This watch affects people in the following weather forecast districts:
Marlborough
Nelson
Canterbury High Country


Scattered heavy showers and thunderstorms are expected over inland parts of the upper South Island this afternoon and evening. For the ranges of Marlborough, Nelson and North Canterbury, there is a risk that some of these thunderstorms could become SEVERE producing localised downpours of 25 to 40mm per hour. Rainfall of this intensity can cause flash flooding and may lead to slips and hazardous driving conditions.

Note: A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms in and close to the watch area. People in these areas should be on the lookout for threatening weather conditions and monitor for possible Severe Thunderstorm Warnings.


For information on preparing for and keeping safe during a storm, see the Civil Defence Get Ready Get Thru website

Issued by: Andy Downs

This watch will be updated by: 09:00 pm Monday 27 November 2017

[Richard]

Looking to my north this storm is close enough to now hear the thump of thunder

[Thunder081]

Here's some photo's from Levin of the CBs over the Tararua Ranges

DSCF6352_1.jpg

DSCF6353_1.jpg

[NZ Thunderstorm Soc]

Nice photos there. The top photo shows a bit of pileus on the tops
Not as good down here sadly, no real build-ups to the west today, compared to later yesterday.

[Thunder081]

Also here's a vid of the slow moving thunderstorms that caused the flash flooding in Roxburgh

[Razor]

Looking to my north this storm is close enough to now hear the thump of thunder

Can see those cloud tops from here

[Richard]

I was working in Lincoln till 3.00 today, i was amazed to be able to see the Molesworth storms from there

[Richard]

Also here's a vid of the slow moving thunderstorms that caused the flash flooding in Roxburgh

And that was captured by a radar 100plus km away too

[NZ Thunderstorm Soc]

Just thinking that in comparison to the "Roxburgh Downpour" as I now call it and judging from the the video shots on TVOne news, the Geraldine Thunderstorm of Oct 24th could of brought the same consequences here but the Geraldine one moved on. I recorded 25mm in just over an hour, where in Roxburgh 40mm in 3 hours was recorded, according to TV One news.
A very slow moving pace or possibly stationary rain cell can cause a lot of damage as depicted yesterday in the Roxburgh Downpour.

[spwill]

The Roxburgh downpour was likely more than 40mm in places John.
More heavy showers in Central Otago this evening but possibly going to miss Roxburgh, looks like a storm near Alexandra just now.

[Andy]

Heavy rain, thunder and lightening here for the pas 1 hour.

[Willoughby]

Heavy rain, thunder and lightening here for the pas 1 hour.

ACCESS-Regional modeled sounding for 8pm showing some steep lapse rates to 700 hPa down Central Otago...

Alexandra-ACC-R.JPG

[NZstorm]

Re Roxburgh flooding
Met Service recorded 29mm in 1 hr. That area seems to have history of flooding when there is a thunderstorm. There was a similar event 30th September last year and I know of others previously.

[Flutterbye]

Re Roxburgh flooding
Met Service recorded 29mm in 1 hr. That area seems to have history of flooding when there is a thunderstorm. There was a similar event 30th September last year and I know of others previously.

It's the hills and valleys right behind the town that causes the problems. If it was on flat land like the aerodrome across the river, then there wouldn't have been many problems. Very common for thunderstorms/downpours up that way but it's unfortunate that the actual town copped it this time.

[NZ Thunderstorm Soc]

Re Roxburgh flooding
Met Service recorded 29mm in 1 hr. That area seems to have history of flooding when there is a thunderstorm. There was a similar event 30th September last year and I know of others previously.

Nearly the same as Geraldine but as I said the Geraldine storm moved on, reducing serious flooding and other associated risks.
I can vaguely remember some events in Roxbourgh years ago as well.
I don't know if I recorded the events in past diaries, will have to check.

[NZ Thunderstorm Soc]

It's the hills and valleys right behind the town that causes the problems. If it was on flat land like the aerodrome across the river, then there wouldn't have been many problems. Very common for thunderstorms/downpours up that way but it's unfortunate that the actual town copped it this time.

I was thinking that maybe the Roxburgh Dam and the lake might of have a contributing effect on this but probably not, mind you the lake will be quite full now.
Were there any substantial localized weather events prior to the dam's construction in the 1960s?

[treetopkk]

always up for a chase tgsnoopy.! Usually when in the waikato the storms focus nth of Hamilton or south of Tekuiti leaving you with a big gap and a tough call left or right? Heading to Wellington on Wed so looking forward to intersecting something

[Thunder081]

Posting these for future reference.

26th November 2017

Mirror: https://flic.kr/p/21QDnb7

27th November 2017

Mirror: https://flic.kr/p/DMGd5U

[tgsnoopy]

always up for a chase tgsnoopy.!

Yeah, I'm a lil far away at the mo

Currently in Darwin hoping for build up storms.

[spwill]

I see Alexandra got 38.4mm (Metservice) yesterday evening.

Interesting to see Milford Sound with only 0.2mm last 18 days, unusual for the month of November.