Thunderstorms Upper North Island - April 19th - 22nd

[NZstorm]

Some unstable weather for northern areas in the coming days. The instability may kick off later tomorrow with isolated thunderstorms with a front/rain that is due Friday pm. Sunday/Monday will see a higher amplitude trough in the Tasman with a better chance of thunderstorms and maybe isolated tornadoes for the west and north of the North island!

Another mild night for Auckland with 18C at 6am.

[Manukau heads obs]

I thought that the latest low might stir up a hornets nest

[spwill]

Lifted index for Monday, some quite cold upper level air moving over northern NZ, hopefully this can eventuate

[jamie]

Haven't seen numbers like that....ever for NZ.

[David]

Lifted index below -4? Not sure I have seen that before either!

[David]

High risk of thunderstorms tomorrow evening. Exciting

Valid to: Midnight Friday 19 Apr 2013

Issued at: 9:30am Thursday 18 Apr 2013

The troughs are expected to move across Northland in the afternoon, and Auckland and Coromandel Peninsula from evening. Temperatures continue to cool in the upper atmosphere. Bands of heavy showers are likely with these troughs. There is a moderate risk of thunderstorms over Northland during the afternoon and evening, bringing strong wind gusts to 90 km/h and localised heavy rain. The risk of thunderstorms becomes high as these troughs reach Auckland and Coromandel Peninsula in the evening. These thunderstorms may produce strong wind gusts of 90 km/h, localised heavy rain, and the chance of a few small tornadoes. A lesser risk of thunderstorms extends over western Bay of Plenty,Waikato,coastal Waitomo and north Taranaki at night.

No thunderstorms expected over the remainder of the country.

http://www.metservice.com/national/warn ... rm-outlook

[Manukau heads obs]

looking forward to it

[ricky]

Great timing . I'm sitting in the airport at Santiago on my way home.. 2 weeks in the tropics and only saw distant thunderstorms..

[Manukau heads obs]

thought you must be home soon...
this wll be a good welcome home present!
been some good rain last few days since you were gone
I guess you were able to keep an eye on your web site while you were gone...

[jamie]

Kool check out the updated thunderstorm outlook. Decent hail possible and small tornados. I'll be in Auckland tomorrow evening for dinner. Perfect timing.

[Manukau heads obs]

sounds like it will peak in time for getting dark ,for a lightning display
might have to meet up for a chase?

[NZstorm]

The jet stream should provide difluence over Northland/Auckland for atleast elevated storms. Just have to see how it shapes up tomorrow.

250mb jet for 06Z according to ukmet.

[NZstorm]

The front crosses Northland this afternoon and Auckland this evening. gfs showing 15mm for Auckland.

UKMET sounding for Auckland NZWP 6pm. CAPE 220j/kg.

[spwill]

Looks like showery spells/possible thunder for the upper North Island out to mid next week.

The coolest morning for a while here, down to 12C.

[NZstorm]

the one thing I don't like about the forecast sounding for NZWP posted above is the weak wind fields. 25kts at 500mb is not overly supportive of thunderstorms. I prefer to see a good 50kt+. The flow is a bit better over Northland closer to the jet.

[Tornado Tim]

Metservices outlook today.

Issued at: 8:54am Friday 19 Apr 2013

An active trough, accompanied by heavy showers and thunderstorms, currently lies over the Tasman Sea and is expected to move across the upper North Island this afternoon and evening. As the atmosphere becomes increasingly unstable, bands of heavy showers and thunderstorms are expected to move onto Northland this afternoon and should spread southwards to reach the Auckland region in the evening and Coromandel Peninsula at night. There is a high risk of thunderstorms with the trough, and these have the potential to bring localised heavy rain reaching 25mm per hour, hail of diameter 5 to 15mm and strong wind gusts around 90km/h. Additionally, there is a risk of one or two small tornadoes. A lower risk of thunderstorms extends farther southeast into western Bay of Plenty, also northern and western parts of Waikato, Waitomo and Taranaki tonight.

Elsewhere, no thunderstorms or significant convection expected.

[Brassnz]

T/S Watch now issued by Metservice for upper N.I.

[jamie]

Lots of activity in behind the first stuff on the rain radar

[Manukau heads obs]

sky here progressively been looking more and more unstable (i.e cloud layers thickening up and lowering)

[jamie]

im beginning to think MS have mis judged where these storms will strike. Im thinking what storms occur will hit the coast of Waitomo and Taranaki. Mainly south of about Raglan. And being further south and away from the jet they will not be as strong as forecast.

Would like to be proven wrong though.

[spwill]

Look for development over our region when the trough comes across, hopefully something of interest can occur around here, certainly looks active west of the upper NI currently.

[David]

Rain rate just hit 109mm/hr here for a few seconds

[Manukau heads obs]

notice towering alto cu to my NW during a break in the cloud a while ago

[Tornado Tim]

Impressive echo returns from a line around 150ks away.

Good amount of lightning emitting from it as well

[Tornado Tim]

Hey NZStorm, in regards to post you deleted it seems this activity is SFC based according to the lightning data flowing in.

Most if not all lightning strikes are around 3-10KA which is typical of a SFC based CB CG. Elevated convection has much stronger current being emitted when a CG strikes and the typical amplitude for those storms is around 19-23 KA.

Here is a lightning map showing all lightning data from within 0-10KA most of it is there bar the odd positive CG.