NZ Weather Forum

That frontal system brought thunderstorms to the west of NZ from Fiorldland all the way up to Auckland as it tracked north.

RODALCO wrote: ↑Tue 27/04/2021 10:21 How do they work out a positive lightning strike, they are usually from the top of the anvil.

I typically look at the waveform that comes back from the Lightning strike the bigger the waveform the higher the KA (Amplitude).

To differentiate -CG and +CG, the Amplitude of the +CG strike is significantly higher than the negative counterparts.
There is no one specific ruleset in a Amplitude rating as to what type of strike it is, it should be judged on the preponderance and relation to others.

Also, the amplitude of said strikes can vary throughout the seasons as our atmosphere around NZ shrinks during the cooler months and expands during the Summer. ie: the Top of a Cumulonimbus may only top out at 7.3Km in height in the middle of Winter and then soar to 14-15 Km in Summer.
The height of a storm increases the resistance and resulting charge of a +CG during a summer storm will usually be higher (although there are some exceptions to this rule)

Apparently there was a lightning strike to the south of Timaru on the night before ANZAC day according to yesterday's Timaru Herald.
I never heard or saw anything. Nothing much overnight with yesterday's front.

Cloudy this evening so can't see the pink full moon.
A rather cool fine day with light south to easterly winds here.
12C for today.

I see MS has twizel on -5.2C at 4am, crazy cold for April.
Edit -6.3C at 7am
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melja wrote: ↑Wed 28/04/2021 04:03 I see MS has twizel on -5.2C at 4am, crazy cold for April.
Edit -6.3C at 7am
Sent from my Armor_3W using Tapatalk

-1 at 9am, yes cold for April.

With regard to +CG vs -CG lightning, I think you can also tell the polarity by the shape of the bolt. Negative lightning tends to branch a lot (the stereotypical "forked lightning" while positive lightning looks more like a single streak that is much brighter than normal.

Snow on Mt Ruapehu yesterday.

After a frost, a fine day. Warmer than yesterday.

The jet stream is currently crossing the equator above NZ, producing an upper equatorial cyclonic vortex. I think this might have come from an abnormally strong Kelvin wave. I've not seen an upper vortex spin out like that from a cross equatorial Jet before. We'll probably know what that means on the surface in about 3 to 4 weeks.

In the northern hemisphere that's an anticyclone, so possibly nothing much. May just fuel the depression north of it.

Chris W wrote: ↑Thu 29/04/2021 14:30 In the northern hemisphere that's an anticyclone, so possibly nothing much. May just fuel the depression north of it.

It may act as a semi stationary node or anchor point in the upper atmosphere which others systems rotate around. As such it could lead to a longish period of blocking patterns for both hemispheres in this part of the globe.

Chris W wrote: ↑Thu 29/04/2021 14:30 In the northern hemisphere that's an anticyclone, so possibly nothing much. May just fuel the depression north of it.

The broad rotating circulation crosses the equator tomorrow morning NZT defying the Coriolis effect which is always stronger at the surface. The upper winds are cyclonic in the Southern hemisphere and anti-cyclonic in the Northern hemisphere for the broad rotation. Can't remember ever seeing that before at a mesoscale level, only synoptic scale level. Something is not right and I think the Kelvin wave might be culprit.

Looks like April in ChCh will finish about Mean temp 0.5C above normal and with 30% of average rainfall

Chalk up yet another dry warm month

Timaru Airport showing max 22C today while Invercargill max 14C/rain.

Mild across NZ today with Ardmore 20C, the high for Auckland area.

NZstorm wrote: ↑Thu 29/04/2021 17:54 Timaru Airport showing max 22C today while Invercargill max 14C/rain.

Mild across NZ today with Ardmore 20C, the high for Auckland area.

16 on my station but 14.6 at In,gill airport with showers.

NZstorm wrote: ↑Thu 29/04/2021 17:54 Timaru Airport showing max 22C today.

Yes another warm day in South Canterbury with 20.5c here, this is the warmest autumn Ive ever seen here by far its crazy. Getting very dry also with no decent rain since January.

20C it got to today. A pleasant day with interesting billow clouds to the NW.
Light winds.
Not expecting much tomorrow under high pressure.

Moderate risk of thunderstorms in North Canterbury this afternoon, low risk for Chch.

22 degrees... and several 20 degree days coming in early May by the looks of things

Southerly wind change has just arrived in Ashburton. A bit gusty but nothing too dramatic.

Chris W wrote: ↑Fri 30/04/2021 11:56 Moderate risk of thunderstorms in North Canterbury this afternoon, low risk for Chch.

Nil risk by the look of it. southerly through now, here.

Looks like SE/W convergence that develops soon going by MS's rain maps, we had some heating up in Amberley earlier and it's reasonably warm albeit cloudy which does mean there's moisture around. Looks like the southerly wind change just went through the city and it seems to be reasonably strong.

Just can't see any chance today

Coming onto drizzle here