NZ Weather Forum

There have been reports of lightning in the NW Arch cloud today.
What could be the reason for this?

The NW arch is then a elevated Cumulonimbus.
Since a NW Arch is an orographic induced cloud,the favourable upper level temps and orographic lifting provided a sufficient lapse rate for lightning to occur.

I wonder if any rain was reported at ground level?

Elevated Cb's don't always have rain reported at SFC due to stable and dry layers beneath where they develop.

Myself and John had been chatting on the phone about why there's been the two lightning discharges here between 6 and 7pm when there's obviously no connection between these and any storms in the mountains or West Coast,even the two strikes didn't show up on Blitzortung,they certainly are the strangest forms of lightning these from NWarches which are nothing like your usual stock standard storms,
Well done Metservice on getting that right but i wouldn't mind knowing what were the clues that enabled them to issue the possibility of it happening

Tornado Tim wrote:The NW arch is then a elevated Cumulonimbus.
Since a NW Arch is an orographic induced cloud,the favourable upper level temps and orographic lifting provided a sufficient lapse rate for lightning to occur.

I wonder if any rain was reported at ground level?

Elevated Cb's don't always have rain reported at SFC due to stable and dry layers beneath where they develop.

Thanks Tim,no there has been no rain at all

Heavy mammatus moving across from the NW this evening including which I took a photo of and is an exclusive for this forum, a penis cloud observed within the mammatus.

Richard wrote:even the two strikes didn't show up on Blitzortung

If they were CC (cloud to cloud) or IC (Intra Cloud) they won't be proceed by Blitzortung. Only CG (cloud to ground) will be......

I wonder if Wellington experienced something along the lines you are describing here at 341am this morning. Was woken from a deep sleep by the longest clap of thunder I have ever heard. Went on for a good 30 seconds, and shook the house. I had not heard anything beforehand, and it was followed by a much smaller clap about 5 mins later, but that was it. A number of other people on twitter also mentioned that it had to be the longest roll of thunder they had heard as well.

Was reasonably steady rain at the time, but nothing torrential that you would normally associate from being under a thunder cell. Looking at the rain radar at the time the clouds were moving from the WSW quite rapidly, yet it was a north westerly outside. There was not an obvious cell evident on the radar either.

The thunder could even be seen detected on the Wellington seismograph drum!!! I have a screen grab I will try upload later.

The length of the rumble just made me think there had to be a significant 'length' of lightning to have caused it to go on and on so long, and that maybe there was some kind of arch cloud higher up above the rain cloud that cold have caused such a situation.

Would be interested to hear comments from other Wellington forum members as to whether it was unusually loud where they were.

NZ Thunderstorm Soc wrote:Heavy mammatus moving across from the NW this evening including which I took a photo of and is an exclusive for this forum, a penis cloud observed within the mammatus.

We want to see your penis John !

BeaconHill wrote:I wonder if Wellington experienced something along the lines you are describing here at 341am this morning.

Well i dont know,the thunder here was different to what you describe,the first clap right over head or near to made us all jump but the noise only lasted 1-2 seconds,second clap was a bit longer but still nothing like a normal storm.

I took photos of the clouds soon after

looking up towards the east roughly where the second strike came from-


And a view of the arch

A warm moist subtropical layer in the upper levels of last nights NZPP sounding. The type of sounding that can produce elevated thunder.

Any ideas why the radar was showing moderate to heavy rain over top here last evening yet there's was none

Richard wrote:Any ideas why the radar was showing moderate to heavy rain over top here last evening yet there's was none

Virga....
Rain that evaporates before it reaches the ground.

Richard wrote:Any ideas why the radar was showing moderate to heavy rain over top here last evening yet there's was none

The low level inversion produced by the warm upper level airmass. It interferes with the radar.

and as Tim suggests, there will be Virga there also.

Lacertae wrote:

NZ Thunderstorm Soc wrote:Heavy mammatus moving across from the NW this evening including which I took a photo of and is an exclusive for this forum, a penis cloud observed within the mammatus.

We want to see your penis John !

Sorry,can't get my new camera to unload images yet, on this computer yet alone the forum

BeaconHill wrote:I wonder if Wellington experienced something along the lines you are describing here at 341am this morning. Was woken from a deep sleep by the longest clap of thunder I have ever heard. Went on for a good 30 seconds, and shook the house. I had not heard anything beforehand, and it was followed by a much smaller clap about 5 mins later, but that was it. A number of other people on twitter also mentioned that it had to be the longest roll of thunder they had heard as well.

Was reasonably steady rain at the time, but nothing torrential that you would normally associate from being under a thunder cell. Looking at the rain radar at the time the clouds were moving from the WSW quite rapidly, yet it was a north westerly outside. There was not an obvious cell evident on the radar either.

The thunder could even be seen detected on the Wellington seismograph drum!!! I have a screen grab I will try upload later.

The length of the rumble just made me think there had to be a significant 'length' of lightning to have caused it to go on and on so long, and that maybe there was some kind of arch cloud higher up above the rain cloud that cold have caused such a situation.

Would be interested to hear comments from other Wellington forum members as to whether it was unusually loud where they were.

There was a report about this on National radio news at 10am. Sadly I only heard half of it.

More here from stuff on the Wellington storm:
http://www.stuff.co.nz/national/8025190 ... ingtonians

Thanks for that Steve. That was probably the report on the news. The forecaster, Andy Down's name was mentioned.

Some interesting comments also from this Radio NZ news-item…

'Thunder caused by stream of highly-charged warm air'

Did some work for some people this morning who live 1km on the Lake Sumner Rd,they said they had small hail about the same time as the lightning,hail from arch cloud!!

We get similar 'elevated' storms when we are under what is known as a Spanish Plume. The mid level dry air comes north from Spain and acts as a cap on any convection from surface heating but as the day ends and the sun goes down these mid layers cool and this has the effect of steepening the lapse rate above this dry 'cap' and elevated convection results. We often get the 'chaotic' skies shown in the photograph earlier in this thread and the storms are in this elevated altocumulus layer. They look impressive on the radar, but a lot of the rain evaporates on the way down. Any lightning can be impressive and the thunder tends to rumble on for quite a time.

Oh thank goodness, I wasn't the only one who heard this.

I woke up to the longest thunder claps I've ever heard. The cats took off and hid. Didn't see any lightning at all for both the thunder claps. They sounded far away but I didn't see any lightning.

BeaconHill wrote:I wonder if Wellington experienced something along the lines you are describing here at 341am this morning. Was woken from a deep sleep by the longest clap of thunder I have ever heard. Went on for a good 30 seconds, and shook the house. I had not heard anything beforehand, and it was followed by a much smaller clap about 5 mins later, but that was it. A number of other people on twitter also mentioned that it had to be the longest roll of thunder they had heard as well.

Was reasonably steady rain at the time, but nothing torrential that you would normally associate from being under a thunder cell. Looking at the rain radar at the time the clouds were moving from the WSW quite rapidly, yet it was a north westerly outside. There was not an obvious cell evident on the radar either.

The thunder could even be seen detected on the Wellington seismograph drum!!! I have a screen grab I will try upload later.

The length of the rumble just made me think there had to be a significant 'length' of lightning to have caused it to go on and on so long, and that maybe there was some kind of arch cloud higher up above the rain cloud that cold have caused such a situation.

Would be interested to hear comments from other Wellington forum members as to whether it was unusually loud where they were.

Finally got round to downloading screen grabs off the iPad.

The first shows the Wellington Seismograph. My wife commented as the thunder rolled on and on shaking the house that it felt like an earthquake, and so I thought I would check to see if anything was detected, and sure enough.
There was a subsequent flash and clap of thunder about 4 mins later. It was smaller than the first, but still showed up. That was it though.

The follwoing is the rain radar for the same time. Certanly no defined thunder cell around at the time. It was raining, but only about 5mm/hour at the time.

500mb (5000m) Vertical velocities at 4am as shown by gfs. Shows good ascending motion near Wellington. Its normal ofcoarse to get the rising motion east of the alps on a NW flow.

I was disappointed that Karen never mentioned the Wellingtonlightning event on this evening's weather.
I thought that was more important than going on about warm temperatures and strong NW winds.
This event being more rare. Was there anything on TV3?

it was written up on the weather highlights board, but I take your point