Thunderstorms/Hail, Eastern SI Lower North 2-4th Oct!!

[Storm Struck]

I thought it was time to create a new topic for this, as some quite unstable air moves onto the south island in the next few days.
A risk exists for Southland and Otago today as MS have indicated, maybe an isolated cell on the coastline around South Canterbury too.
But the main set up is much better for tomorrow, especially for the eastern South Island and the west coast too.
A frontal band goes through around 1pm over Mid Canterbury tomorrow, but it probaly only initially presents low/moderate chance as there is a pre frontal westerly.
However a cold pool of air is left behind as an upper level trough develops over Mid Canterbury further bringing the atmosphere more unstable and allowing some pockets of coastal E-SE winds especially through the Christchurch area.
I highlight possibly our first high risk set up of the season between Ashburton and Christchurch, where we have -3 LI's 500-600 cape -34C upper air and reasonable convergences could lead to hail of 20+mm.
Well worth the chase tomorrow especially late afternoon/evening.

[Storm Struck]

I would love to know what MS is looking at
http://www.metservice.com/warnings/thunderstorm-outlook

[Bradley]

Wow. One of you is very wrong in their forecast! All your numbers stack up though so it will be very interesting to see what happens tomorrow afternoon...

[melja]

I think the frontal band will kill off and chance of thunderstorms after it pass, just my guess

[mikestormchaser]

I think the frontal band will kill off and chance of thunderstorms after it pass, just my guess

I know what you mean melja. The numbers stack up nicely as jase has pointed out. My main concern would be cloud cover. Heating not an issue for me as the upper air is so cold. But often after a frontal band it can clear then that unstable air comes in. Classic stuff really. Im going moderate risk tomorrow in canterbury. Be interesting to see what Metservice update there risks tonight.

[RichyDunedin]

High cloud all day here and not very warm. Moderate risk of thunderstorms this arvo, evening and even tomorrow morning which seems strange. Metservice not giving you Cantabrians much hope haha.

[Storm Struck]

The frontal band which comes through around midday could briefly destabilise things of course with the risk of thunderstorms, but generally once a front goes through which this will be brief will clear the skies inbehind and the SW dies off.
I guess its more a case of whether it swings back to the westerly quarter or a breezy coastal E-SE, which is quite likely looking at some of the maps especially around mid canterbury where the isobaric flow wants to open up a tad and develope a small offshore low from Banks Peninnsula.
Either way I still think it is worthy of a risk rather than giving no risk given the conditions are so fruitful.
Secondary trough in the evening with colder air boom

Take a look at this map although I am not a great fan of METVUW and thier recent map changes, this kinda shows what I mean by looking at the change in windsocks over mid canterbury compared with the rest of the south island.
It could be upper level W-SW but at the surface the winds are more coastal E-SE, which could make things rather interesting .
Worth noting I think, sometimes its best to over look these things and learn more from them.

rain-nzsi-2014100112-42.gif

[Paul Mallinson]

The problem for Canterbury tomorrow is that although the deep atmosphere is potentially unstable, the problem is whether or not the surface wind convergence will be strong enough and will the moisture be enough. Soundings today suggested trouble getting decent parcel lift off the surface with some negative bouyancys to be overcome. If the wind convergence is strong enough, then the moisture in the easterly will likely be high enough. We did allude to this in the text for the afternoon/evening period.

Paul

[Tornado Tim]

Ah very good Paul, I knew you'd post sooner rather than later .
Ill have to schedule another time to come to the Metservice Office, next time I am coming is in November.

I hope for you folk in Canterbury get a storm tomorrow, been a while since you last had a good one.

[NZ Thunderstorm Soc]

The problem for Canterbury tomorrow is that although the deep atmosphere is potentially unstable, the problem is whether or not the surface wind convergence will be strong enough and will the moisture be enough. Soundings today suggested trouble getting decent parcel lift off the surface with some negative bouyancys to be overcome. If the wind convergence is strong enough, then the moisture in the easterly will likely be high enough. We did allude to this in the text for the afternoon/evening period.

Paul

Sort of some ways, I do tend to agree with Paul.
It's a matter of timing and getting things into prospective.
I'm forecasting a, basically, fine day with cold SW winds.
There could be 'Cb Coldies" off shore.
Maybe a wintry shower may move through?

[03Stormchaser]

I'm busy tomorrow unfortunately setting up a friends wedding I'm a groomsman at. I can see the risk there, but can also see where Paul is coming from. Maybe we are just getting to excited for the first storm of the year

[NZstorm]

The set up looks too weak on moisture but I still expect some cloud development capable of a few lightning discharges near the coast.

[Storm Struck]

Abit of an earlier than expected SW change this morning nice gust front with it and some quite heavy rain bands on the radar, could even be some lightning in the stuff down near Timaru.
Even though we have an early southerly its not a bad thing just means we boot the westerly out earlier once this stuff clears off and hopefully allows coastal winds to kick in.

[RichyDunedin]

Was awoken a couple times last night by loud rolling thunder. Sometime between 2-4am.

[Nev]

This morn's MS update for today not too different from last night…

MetService - Thunderstorm Outlook

Valid to: Midnight Friday 3 Oct 2014
Issued at: 9:03am Friday 3 Oct 2014

The cold showery outbreak, bringing snow to low levels in the South Island, spreads over the North Island this afternoon (see Special Weather Advisory,Severe Weather Warnings and Watches for further detail).

There South Island a high risk of squally thunderstorms in most southern and western areas from Southland to northwest Nelson. Brief heavy rain, snow lowering to 2-300 metres in the far south, hail, and gusts around 90km/h are likely to accompany these storms.

A moderate risk extends into Taranaki and Manawatu during the evening and night. Here too they may be squally with small hail and gusts of 90km/h.

In Canterbury, there is a moderate risk of thunderstorms as a southwest change moves up the east coast in the afternoon. Any thunderstorms that do develop here are likely to bring localised heavy rain of 10-15mm/hr, and hail of 10-15mm diameter - possibly even 20mm.

A larger area of low risk covers much of the South Island, and the southwestern North Island, as indicated on the chart.

No thunderstorms expected elsewhere.

MetService T-Storm Outlook Map, Is. am for Oct 3.png

[Storm Struck]

Clouds beginning to gradually clear now as the shower activity peters out, SW wind easing back too .
I dont see the westerly returning after this, id say it will be all coastal onshore winds before the change late this afternoon.
Abit more moisture this morning than I was expecting too going by the surface maps, just over 5mm although some of that would have been from convective deeper clouds too.
The area MS indicate is about where I would pick for the best chances of storms, Crossing everything well not everything for this afternoon and a good chase.

[Razor]

We now how the requesred sun, and perhaps a wee wind shift might help. Soem towering cumulus to the far SW now, as observed from the 6th floor of the CBD

[Orion]

Some explosive-looking cloud to the south of Ashburton, can't tell yet how far away it might be.

[Storm Struck]

All ingrediants are there for storms now, heating NE winds here in Rolleston and a few CB's already blowing up to the south.
New development inland near Mt Somers

[matttbs]

A decent looking shower heading up past mt peel, saw a flash

[Orion]

I may have just heard a roll of thunder?

[matttbs]

Yea lots of thunder as lightning. I'm already getting small hail and it's still miles away

[matttbs]

Just had a mental hail storm, 25mm hail

[Paul Mallinson]

Just had a mental hail storm, 25mm hail

Interesting report. Where did this occur? HInds? Radar doesn't show anything significant around this time.

Paul

[Razor]

Just had a mental hail storm, 25mm hail

Interesting report. Where did this occur? HInds? Radar doesn't show anything significant around this time.

Paul

I think hes up nearer the foothills these days Paul