We had 2 "flicks" today - the afternoon one came in around 4.30-5.00 but I saw only sleety showers in the downtown area. Clear again by 6.30.tich wrote:Trademe Forum reports of the white stuff in Masterton, Wainuiomata and Wellington hill suburbs too - funnily, news item had just said that Wellington had escaped the stormy weather that was plaguing other parts of North Island.Snow in Lower and Upper Hutt...
Only 7C at Awhitu at 4pm - were you getting hail Brian?
Icy flick 8-10th October
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Photo I took to day from a passing cb about lunchtime.
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Yes, the upper air temps were very cold -38C at 500 hPa over Invercargill and about -35C over central New Zealand. But the temperature profiles were capped just above this level and so there was good bouyancy (CAPE) up through to about 20,000ft and then warm temps above. This limited the depth of the convection and the amount of lightning. (I've always used as a rough rule that CB tops need to go above about 20,000ft to get lightning when doing a parcel lift on a sounding).
But with the good bouyancy in the low and mid levels, this produced the sort of hail seen in Auckland (and elsewhere) (very informative hail picture NZStorm). At the same time, temperatures around 10 to 12C and dew points around 2 to -2C were seen from central parts down to Canterbury - and about 15-17/6 upper North Island). These sfc values along with along with dry layers aloft and near the surface on the Paraparaumu and Whenuapai soundings brought strong outflow winds to the surface, cooled temps off by about 5 to 7C as squall lines passed, and also snow pellets to virtually sea level in the Wellington area yest afternoon.
There were several areas of wind convergence at the surface that passed over the North Island. A couple of notable ones apart from what happened in Wellington was a squall line that passed through Taupo which gave a gust of 55kts from the gust front and the line of thunderstorms that went through Auckland at midday stayed intact and moved over the Whagarei area about 3pm giving a gust there to about 60knots.
So a very interesting weather day all in all. It just shows you that instability is a relative thing. Even if the surface dewpoints are quite low, you can still get good convection if the upper air is sufficiently cold.
Paul
But with the good bouyancy in the low and mid levels, this produced the sort of hail seen in Auckland (and elsewhere) (very informative hail picture NZStorm). At the same time, temperatures around 10 to 12C and dew points around 2 to -2C were seen from central parts down to Canterbury - and about 15-17/6 upper North Island). These sfc values along with along with dry layers aloft and near the surface on the Paraparaumu and Whenuapai soundings brought strong outflow winds to the surface, cooled temps off by about 5 to 7C as squall lines passed, and also snow pellets to virtually sea level in the Wellington area yest afternoon.
There were several areas of wind convergence at the surface that passed over the North Island. A couple of notable ones apart from what happened in Wellington was a squall line that passed through Taupo which gave a gust of 55kts from the gust front and the line of thunderstorms that went through Auckland at midday stayed intact and moved over the Whagarei area about 3pm giving a gust there to about 60knots.
So a very interesting weather day all in all. It just shows you that instability is a relative thing. Even if the surface dewpoints are quite low, you can still get good convection if the upper air is sufficiently cold.
Paul
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Thanks Paul. I'm no expert in technical meteorology, but that was an interesting explanation. The air over NZ was certainly very cold and unstable - the squall lines sending the temperatures plummeting and snow/snow pellets falling to below the 800m forecast by MetService. (Taupo only 4C at 1pm yesterday - must've been snow or sleet nearby)
I've heard about simiar situations in past springs, eg late September 1977, when hail fell in many northern areas. The NZ Herald then reported snowflakes even in parts of central Auckland and Waiheke Island, plus a blanketing in Matamata. This could easily have been in the form of snow pellets, like what the Wellington area got yesterday.
I've heard about simiar situations in past springs, eg late September 1977, when hail fell in many northern areas. The NZ Herald then reported snowflakes even in parts of central Auckland and Waiheke Island, plus a blanketing in Matamata. This could easily have been in the form of snow pellets, like what the Wellington area got yesterday.
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Yes, I use 7000m as the level for thunder. But recently I read that lightning had been observed in cb tops of only 5000m in a study in Japan.I've always used as a rough rule that CB tops need to go above about 20,000ft to get lightning when doing a parcel lift on a sounding).
But that was in a polar air mass.
I think this was the coldest airmass to strike NZ this year but I'll need to check that.
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Have a pretty good feeling it was.. LAPS was progging 518dm thickness over Dunedin at 4am yesterday.NZstorm wrote: I think this was the coldest airmass to strike NZ this year but I'll need to check that.
Blotches of snow on the northern-lower part of SH 47 from yesterday's fall.. snow was melting quite quickly today at the top of the Bruce in the sunshine. The freezing rain we had around lunch was quite painful I might add!
I disagree, seen numerous times here with Cb tops to 4000m with 10+ CG discharges. (29 Sep for example). But recently I read that lightning had been observed in cb tops of only 5000m in a study in Japan.
But that was in a polar air mass.
Also a few times here with weak IC and cumulus mediocris in the right (usually humid) conditions.
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Yes, I think they were higher. I took a look at the Whenuapai sounding for noon Sept 29 and using Temp=20 and Dewoint (Td) = 12 for Hamilton, and this pointed to CB tops to 25000-30000ft and max tops to about 350000 (T= -52C). There was a convergence line to the east of Hamilton and a concentration of lightning strokes there.
In the mid 70's, I spent 18 months on Campbell Island and during that time we saw CBs with classic anvil shapes moving through all the time, yet I only ever observed one flash of lightning. I was peering into a Stevenson screen at midnight on New Years Eve and the next second - poof! and that was it!).
I think the comment about the Japanese study with tops to 5000m is reasonable, but in my experience, with tops much lower than that, lightning is quite rare.
Paul
In the mid 70's, I spent 18 months on Campbell Island and during that time we saw CBs with classic anvil shapes moving through all the time, yet I only ever observed one flash of lightning. I was peering into a Stevenson screen at midnight on New Years Eve and the next second - poof! and that was it!).
I think the comment about the Japanese study with tops to 5000m is reasonable, but in my experience, with tops much lower than that, lightning is quite rare.
Paul
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i remember when living in the waikato observing some spring style storms with very low tops and the odd flicker of lightning, so I geuss in a way I can back up (to a point) what the fogster is saying.
Its funny too cos i have seen on many occasions down there, C-C in non-glaciated Cb's? anyone else ever seen this?
Its funny too cos i have seen on many occasions down there, C-C in non-glaciated Cb's? anyone else ever seen this?
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Sorry but I still disagree..
http://www.weatherforum.org.nz/forum/vi ... 7093#37093
That afternoon Cb shot had heights of 8-9500m
The sunset Cb (T/Cu there in it's early stage..) was 20-30km away, and looking at it again it probably had heights of 5-6000m. Pileus cap there with several CG's. We also get the rare occurance of dry lightning (IC).
You might not experience this in the maritime-effected meso-climate of Auckland, but we certainly do here!
http://www.weatherforum.org.nz/forum/vi ... 7093#37093
That afternoon Cb shot had heights of 8-9500m
The sunset Cb (T/Cu there in it's early stage..) was 20-30km away, and looking at it again it probably had heights of 5-6000m. Pileus cap there with several CG's. We also get the rare occurance of dry lightning (IC).
You might not experience this in the maritime-effected meso-climate of Auckland, but we certainly do here!