NZ Weather Forum

Thunder081 wrote:Here's a timelapse of when that low passed over Auckland on the 15th of October looks cool when it passes over the Hauraki Gulf and out to sea.

Thanks for the clip thunder081. Pity that cold pool crossed in the morning. Auckland would have got a thunderstorm from an afternoon passage.

Windy NW day here today .

A holiday weekend coming up, Saturday looks mostly fine for NZ but for some showers about the eastern NI Ranges/ Gisborne, Sunday increasing cloud. Monday some rain or showers likely for many areas.

Follow the links guys to give the government feedback on the extremely poor standard of data access Metservice and NIWA currently give the public, looks like they are finally listening!!

http://www.weatherwatch.co.nz/content/h ... ather-data

Will this be the end of "Short" forecasts?

Watching Friday's polar trough set up over the North Island but so far thunder/hail potential looks south of Hamilton.

NZstorm wrote:Watching Friday's polar trough set up over the North Island but so far thunder/hail potential looks south of Hamilton.

Worth a chase I think if the set up comes further north, should be plenty of sunshine in the weather mix for Waikato Friday .

Convection looks quite low topped on Fridays setup, but the steep lapse rates should be able to get some Lightning out of it, depending on low forecast octas.

Up to a nice 21.9C here today, warmest of Spring so far.

Tornado Tim wrote:Convection looks quite low topped on Fridays setup, but the steep lapse rates should be able to get some Lightning out of it, depending on low forecast octas.

A good way of judging lightning potential is to look at the temperature at the top of the convection. If it is colder than -20C, some potential exists. On Friday cb tops look to be about -38C which is a good number.

NZstorm wrote: A good way of judging lightning potential is to look at the temperature at the top of the convection. If it is colder than -20C, some potential exists. On Friday cb tops look to be about -38C which is a good number.

But that doesn't take into consideration the moisture and associated charge differentiation that occurs with a higher WV percentile with a parcel rising say from 700hpa to the trop.

I could say that cloud tops are unduly cold, like typical coldie or Winter time CB's in similar cold pools or cold troughs, but they quite often in NZ just spit out hail and have little to no lightning due to the fact they have been moisture starved.

So both need to be used in combination with each other, along with comparing parcel rise from set point with the sat adab lapse rate.

Tornado Tim wrote:

NZstorm wrote: A good way of judging lightning potential is to look at the temperature at the top of the convection. If it is colder than -20C, some potential exists. On Friday cb tops look to be about -38C which is a good number.

But that doesn't take into consideration the moisture and associated charge differentiation that occurs with a higher WV percentile with a parcel rising say from 700hpa to the trop.

I could say that cloud tops are unduly cold, like typical coldie or Winter time CB's in similar cold pools or cold troughs, but they quite often in NZ just spit out hail and have little to no lightning due to the fact they have been moisture starved.

So both need to be used in combination with each other, along with comparing parcel rise from set point with the sat adab lapse rate.

Yes, convection has to be robust otherwise not a lot will happen.

The other part of the equation is the convective cells have to be at least 3km deep above the freezing level. These are the criteria BOM used in setting up their lightning forecasting. There was an interesting paper written on the topic.

The total totals at 7pm tomorrow. Late day convection will be placed between Hamilton and Taupo.

Ricky has found that if there is a dry layer in the atmosphere that can help with the charge separation?

Pretty uneventful sporadic spitty rain so far here in ChCh. Looks like some decent rain further south

Razor wrote:Pretty uneventful sporadic spitty rain so far here in ChCh. Looks like some decent rain further south

Rain sounding on the roof here at present

Razor wrote:Pretty uneventful sporadic spitty rain so far here in ChCh. Looks like some decent rain further south

More than sporadic now here in the city

Yup good or the garden, welcome falls!

Steady but not 'thundering' down rain for today.

Even getting some rain here.

Manukau heads obs wrote:Ricky has found that if there is a dry layer in the atmosphere that can help with the charge separation?

Yes, the air within a cb rises faster when the air aloft is dry. Warm moist air is less dense than a cold dry air.

When looking at forecast sounding you don't want to see a moist profile. You want dry mid level air.

Nearly 30mm here and still coming down good.

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Nearly 80mm of rain for Christchurch in 6 weeks, quite decent to say the least!!

Yes and very regular out this way too.

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Bradley wrote:Nearly 80mm of rain for Christchurch in 6 weeks, quite decent to say the least!!

Where's that station Bradley? More like 45mm around our part of town in past two months here. A lot of the rain seems locally heavy wit recent events, very hit and miss. 7mm here so far today