Convection Period 1st - 4th Jan

[Richard]

Looking likely now a prolonged period of instability starting Monday throughout much of inland areas of both islands then retreating to mainly to the North Island towards the end of the period.

[spwill]

Tuesday looks like the first significant day, some good numbers for Waikto on Tuesday.

[Richard]

Looking like Wednesday could be the best chances for us cantabs

[NZstorm]

Showalter index chart for Wednesday.

The showalter index is an instability parameter that is suggestive of good storm activity when below zero.

Numbers of -3 over South Island suggest hail possible with storms on Wednesday.

[Richard]

Dont want hail, a gardeners worse nightmare. Mind you haven't seen large hail in 17 years here

[NZstorm]

Some downpours over Auckland this afternoon. Parts of the North Shore got up to 28mm in an hr according to the PWS.

[NZ Thunderstorm Soc]

Showalter index chart for Wednesday.

The showalter index is an instability parameter that is suggestive of good storm activity when below zero.

Numbers of -3 over South Island suggest hail possible with storms on Wednesday.

Looking good for Geraldine but I think we have had our share of thunderstorms so far this thunderstorm season

[Richard]

Looking good for Geraldine but I think we have had our share of thunderstorms so far this thunderstorm season

What!!, you scared of over dosing

[NZ Thunderstorm Soc]

What!!, you scared of over dosing

Yes, well since moving here, we have seemed to of had more thunderstorm related activity than the time we were in WM especially in the later years ?.
With this oncoming event , it seems that rain will fall in areas that don't really need it, ie BOP and the Kaikoura Coast. Don't want the road and rail closed again from slips

[tgsnoopy]

With this oncoming event , it seems that rain will fall in areas that don't really need it, ie BOP and the Kaikoura Coast.

We could do with rain here in the Western BOP, we haven't had a lot of late, but we don't need heavy rain like we got recently (Flooding is no fun).

I'm, watching this develop with interest & some concern.

[treetopkk]

Wind /depression will ruin convection chances thurs . Hopefully it will weaken and stay around for some good action in the weekend, no shortage of moisture now and still in that "blocking" pattern.

[NZstorm]

Wednesday looking drier over Canterbury now such is the fluctuations of the models. Looks more favourable today over the foothills.

North Island has fairly weak lapse rates today and a lot of precip. Tomorrow looks a bit better.

[Razor]

Heading up the Hope tramping next couple of days. Eyes on the skies!

[tgsnoopy]

From Metservice:
http://www.metservice.com/warnings/thunderstorm-outlook

TO2Jan18.gif

Thunderstorm Outlook
Valid to: Midnight Tuesday 2 Jan 2018

Issued at: 8:37am Tuesday 2 Jan 2018

The combination of a warm humid day and light winds will allow daytime cloud buildups to produce scattered heavy showers and thunderstorms across many parts of the North Island and inland South Island today.

In the North Island, the main risk of thunderstorms is from Auckland and western Coromandel Peninsula southwards to Wairarapa with a surrounding low risk covering many other parts of the North Island as indicated on the chart. These thunderstorms will be slow-moving and accompanied by localised heavy rain. Many of the storms could severe with localised downpours of 25-40mm/hr (or even 50mm/hr, especially about the central North Island). Rainfall rates of this intensity can cause surface and/or flash flooding, and make driving conditions extremely hazardous.

In the South Island, there is a general low risk of thunderstorms about many inland areas from Marlborough and Nelson to central Otago, but this risk of storms is considered closer to moderate about the ranges of Nelson lakes,southern Marlborough and North Canterbury as indicated on the chart. Localised heavy rain will accompany any storms that develop.

No other thunderstorms or significant convection expected over New Zealand today.

[tgsnoopy]

And again...
http://www.metservice.com/warnings/seve ... torm-watch

TW2Jan18.gif

Severe Thunderstorm Watch
Issued by MetService at 08:44 am Tuesday 02 January 2018
Valid until 10:00 pm Tuesday 02 January 2018
This watch affects people in the following weather forecast districts:
Auckland
Coromandel Peninsula
Waikato
Waitomo
Taumarunui
Bay of Plenty
Rotorua
Taupo
Gisborne
Hawkes Bay
Taranaki
Taihape
Wanganui
Manawatu
Tararua
Wairarapa

The combination of a warm humid day and light winds will allow daytime cloud buildups to produce scattered heavy showers and thunderstorms over many parts of the North Island (especially from Auckland southwards), and over the northern South Island, this afternoon and evening.

These thunderstorms will be accompanied by localised heavy rain or downpours.

In the North Island, from Auckland and western Coromandel Peninsula down to Wairarapa, including the ranges of Gisborne and Hawkes Bay, many of these thunderstorms are expected to be severe, especially inland and particularly about the central North Island, where rainfall rates of 20 to 40mm/hr (or even 50mm/hr) are likely.

Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.

Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain.

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: John Crouch

This watch will be updated by: 02:00 pm Tuesday 02 January 2018

[Richard]

Cloud buildups are happening not that far off to the west and north and its only just after 10.00am, thats very early for around here.

[NZstorm]

Early tcu development around here too with even some weak glaciated cb/showers out to NW. No capping today so early cloud development. Airport already on 23C.

[David]

It's certainly humid, dewpoint 19-20C today

[Tornado Tim]

The ECMWF CAPE forecast is showing quite a bit of instability, it usually is far more conservative and less fluid than GFS.
Low shear, zero cap, with moderate to high sfc moisture, and decent resulting lapse rates = pure precip dumping storms.
Not sure if Ill chase, dont really like these setups as much, unless something is close as storms collapse far too quickly for my liking.

[spwill]

Some Cbs in the west already, 24C dewpoint 20C

[Cyclone Tracy]

25c and a 21c dew point now here with sun in the mix. Getting close to popcorn time.

[Razor]

In culverden, 11:30am warm sunny light breeze. Not much in the way of cloud buildups although some minor cumulus developments to the west. Will see what the arvo brings as we wander deep into the ranges...and tomorrow maybe

[tgsnoopy]

Update:
http://www.metservice.com/warnings/thunderstorm-outlook

TO2Jan18b.gif

Thunderstorm Outlook
Valid to: Midnight Tuesday 2 Jan 2018

Issued at: 10:16am Tuesday 2 Jan 2018

Updated at 10am Tuesday to extend low risk to include Hauraki Gulf and Great Barrier Island.

The combination of a warm humid day and light winds will allow daytime cloud buildups to produce scattered heavy showers and thunderstorms across many parts of the North Island and inland South Island today.

In the North Island, the main risk of thunderstorms is from Auckland and western Coromandel Peninsula southwards to Wairarapa with a surrounding low risk covering many other parts of the North Island (including Great Barrier Island)as indicated on the chart. These thunderstorms will be slow-moving and accompanied by localised heavy rain. Many of the storms could severe with localised downpours of 25-40mm/hr (or even 50mm/hr, especially about the central North Island). Rainfall rates of this intensity can cause surface and/or flash flooding, and make driving conditions extremely hazardous.

In the South Island, there is a general low risk of thunderstorms about many inland areas from Marlborough and Nelson to central Otago, but this risk of storms is considered closer to moderate about the ranges of Nelson lakes,southern Marlborough and North Canterbury as indicated on the chart. Localised heavy rain will accompany any storms that develop.

No other thunderstorms or significant convection expected over New Zealand today.

[jamie]

Got thunder from the storm in behind Ngaruawahia and thunder from the little cell to my east. Just got home too from a holiday at kuratau. Showers on off all the way home.

[spwill]

The Auckland convergence line today is over west Auckland, fine at my place.
Photo of Cb line in the west, pulse showers with isolated storms showing up.