NZ Weather Forum

Cant see bugger all to the south here at the moment, but at least the wind has died

Southerly through here now with a bit of a delapidated wall cloud. Nothing sexy at all
Huge temperature drop of about 0.3 of a degree Celcius

JohnGaul
NZThS

NZ Thunderstorm Soc wrote:Southerly through here now with a bit of a delapidated wall cloud. Nothing sexy at all
Huge temperature drop of about 0.3 of a degree Celcius

JohnGaul
NZThS

Oh no,its even looking badder now

Temp dropped 5 degrees within 2 minutes

Clouds have really gone bonkers, can see the southerly coming and one lightning flash to the SW about 5 minutes ago.

Only one sferic so far picked up here with this scenario,

JohnGaul
NZThS

Has been nothing on this Lightning tracker for Canterbury, so any lightning activity will have been very weak.
http://webflash.ess.washington.edu/L_pl ... er_map.jpg

As others have said the NW tends kill TS chances down there.

Went out to the airport, didnt see any flashes and checking tracker nothing being picked up, wee bit disappointing but that NW just killed it all.
Gust front moving over.

Thats a nice pic of the gust front steve.
Yeah i think that W/NW did kill it all!! just cant wait for the sea breeze to really kick in witch shouldnt be to far away.

Yes, well after the violent earthquake this morning, I think that most Cantabrians will not be wanting a thunderstorm with booming overhead instead of from the ground below.
I symphasize with them.
Yes, the Nor-wester did stuff up this scenario and the change was quite moderate considering the warnings put out by MetService, today.
Raining nicely now but not heavy and squally which they could of been if it wasn't NW previous.

JohnGaul
NZThS

Good pic Steve.

The NorthEaster is often a key ingredient for storms along the SI east coast, by December it kicks in most days. Provides convergence and moisture.

spwill wrote: The NorthEaster is often a key ingredient for storms along the SI east coast, by December it kicks in most days. Provides convergence and moisture.

Correct

JohnGaul
NZThS

It is a pitty nothing eventuated but oh well still early days for storms.
I see most of Canterbury is getting good rain at the moment, you wouldnt believe its dry as a bone here just some brief spots earlier on.

Jasestorm wrote:It is a pitty nothing eventuated but oh well still early days for storms.
I see most of Canterbury is getting good rain at the moment, you wouldnt believe its dry as a bone here just some brief spots earlier on.

Not alot here either, had more light drizzle then anything before, and light spots before to.

03Stormchaser wrote:Went out to the airport, didnt see any flashes and checking tracker nothing being picked up, wee bit disappointing but that NW just killed it all.

PA1910791.jpg

Gust front moving over.

Here's my picture, looking towards TC.

JohnGaul
NZThS

Oh well had our storm here in rangiora on monday arvo

This is an interesting phenomena for us Brits, as we dont see anything like this, especially in the middle of the afternoon. I noticed the following METARS for Christchurch for the 19th and am rather puzzled as to an explanation.

0200Z 32006KT 230V060 CAVOK 20/04 Q997
0500 27018KT 230V290 CAVOK 17/03 Q997 TEMPO 23030G45KT 3000 +SHRA BKN014 BKN020CB
0600 19024KT 9999 VCSH SCT020 09/07 Q1000 TEMPO 3000 +SHRA BKN014
0700 19020KT 9999 -SHRA FEW010 SCAT015 BKN040 08/07 Q1001 TEMPO 3000 +SHRA BKN014

Was this a frontal passage or something like the southerly buster in Aussie? There is a big temperature drop with the wind backing from W to S, but before any rain had fallen. I would be most interested in an explanation of this event. Something similar happened at Wellington Airport 6 hours later, but not so pronounced.

The S change/front is stable due to dry air coming in off the Southern Alps (pre frontal fohn NW flow). The precipitation occurs within moist cold advection behind the wind change.

Say in Greymouth the front can be overhead them wheres in Chch (same latitude) at the same time it be dry.They can even for a short period in the east get warm southelies.The front lags in the east.

Thanks Steven. You mentioned 'southerly change' and Google has come up trumps with a couple of pdf's for me to read. I suspected that the Alps were important contributors...it looks like some sort of gravity wave.

http://www.meteo.physik.uni-muenchen.de ... h_etal.pdf

http://www.bom.gov.au/amm/docs/2003/reeder.pdf

Simon Culling wrote:Thanks Steven. You mentioned 'southerly change' and Google has come up trumps with a couple of pdf's for me to read. I suspected that the Alps were important contributors...it looks like some sort of gravity wave.

http://www.meteo.physik.uni-muenchen.de ... h_etal.pdf

http://www.bom.gov.au/amm/docs/2003/reeder.pdf

Its a cold front.

Succinctly put Tony

Hey, Tony + Cantygal. I'm not so sure it is just a cold front. The structure displayed in the two studies quoted do not show classic kata or ana cold front characteristics at all.

The NW winds ahead of the 'front' approaching from the south warms the air by adiabatic compression and the Alps appear to distort the front so that it stalls to the west of NZ but the mountains produce a low level cold surge (a density or gravity current) up the east side of NZ that effectively disconnects the frontogenesis from the front, hence many of these changes do not have much rain. The temperature contrast comes from the foehn wind ahead of the fornt warming the air and the low level current drawing in cold air from the cold sea. Voila.

Heavy shower and hail an hour ago here, looking dark to the south again, and I thought I heard thunder but nothing on the lightning detector.

Some towering CU about the area in the last hour or so. Bubbling away for sure with the sun out. Radar doesnt seem to have much on it.

wow a real intense one on noon radar actually, Very small blob but intense!