Amuri area's northwestly Sheet lightning

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Richard
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Amuri area's northwestly Sheet lightning

Unread post by Richard »

I''ve recently joined this forum and have been impressed with how many other fellow weather enthusiasts are here,i have made a resent observation that i would like to share with you all, hopefully someone may have some answers or ideas that helps me understand what drives such a weather feature.
I lived most of my life in Rangiora,any storm enthusiasts who lives on the Canterbury Plains understands what produces electrical storms in that area,the last ten years i have lived on the Amuri plains which has a completely different weather pattern to the rest of Canterbury.This area has three different storm types,(0ne) has the typical heat build up cold front storms,but not as common as on the Canterbury Plains.(two)has more of the common summer thermal cloud build ups that can move from the NE direction around to the west,often storms can develop over head,go through all the stages of maturity and dissipate over the same spot,they are the ones i really enjoy.
But its the third type of local storms that has me puzzled,a few days ago we like a few others in inland Canterbury
experienced lightning from a northwester.I can recall at least ten of these separate storm events of this type over the last ten years,its always sheet lightning earthing out in the mountains and this is the part that i cant figure out and that it is always at night,never in the day time, :?: why???
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Re: Amuri area's northwestly Sheet lightning

Unread post by mikestormchaser »

Hi Richard :) im no expert at all on the weather and storm but am a enthusiast in it just like yourself.
Not sure why that is, just a guess that things tend to heat up more at night with the NW flows and active fronts perhaps?

NZstorm would most likely be able to explain and tell you how it works.
NOTE: the lightning at night probably makes things look closer and worse, then what it seems during daylight aswel?
Nt that ud see sheet lightning bouncing off clouds during the day from the west as its lil to bright :P :wave:
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Re: Amuri area's northwestly Sheet lightning

Unread post by Storm Struck »

Alot of the lightning strikes i notice to the west tend to be blue flashes which indicate as you have said sheet lightning.
I believe there are certain types of lightning depending on what kind of storm it is and the daytime temperatures/ relative humidity etc.
West coast storms would produce more blue sheet ligthning than CG cloud to ground, because they are more super saturated storms most of the time instead of thunderstorms out east which bring hail often.
I did however notice and hard to miss atleast 3 of the lightning flashes on Tuesday night were yellow and quite bright, like someone had taken a photo of the Canterbury region from the Alps.
I figured these could have been more a CG strike than an IC inner cloud or CC cloud to cloud.
As for the night time thing its really hard to answer, is it purly just timing and coinsidence that the fronts or troughs from the west come up late afternoon/evening or is there another factor we are missing.
Actually to note Richard eastern Canterbury/Christchurch and surrounds hadnt had a proper day time storm for about 3 years until January this year.
Normally our storms would come through at night which was always fun, but not so when filming and having a black screen with a flash every 30 seconds or so :lol: great at the weather meetings.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Tornado Tim »

tornadoman18 wrote:Hi Richard :) im no expert at all on the weather and storm but am a enthusiast in it just like yourself.
Not sure why that is, just a guess that things tend to heat up more at night with the NW flows and active fronts perhaps?
I agree with you Tornadoman, Though I am not familiar with Canterbury at all I will just say this.
From my understanding If the day has been sunny the land temperature will be allot warmer and when it hits nightfall the warmth from the ground the start to warm the cooler air just above the ground and then cause that to rise.
As the warm air rises cooler air will replace it and start to warm up as well, this may very well help the formation of thunderstorms if a body of cold air shift on top of the warm air below, such as a cold front.
As for colours of lightning, they state what is within the thunderstorm or Cumulonimbus clouds and air.
The reason of this is the optics of light, and what beam of the spectrum the light or lightning beams off ( i am not going into further detail as this leans into chemistry and the structure of matter)
Just as a rule of thumb, for the colours of lightning strikes:
Red- Rain
Blue- Hail
Yellow- Dust
White- Low Humidity
Pink- Rain and hail
Hope this helps :smile:
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Re: Amuri area's northwestly Sheet lightning

Unread post by spwill »

But its the third type of local storms that has me puzzled,a few days ago we like a few others in inland Canterbury
experienced lightning from a northwester.I can recall at least ten of these separate storm events of this type over the last ten years,its always sheet lightning earthing out in the mountains and this is the part that i cant figure out and that it is always at night,never in the day time, why???
Much of the lighting with these storms will be very distant so your not going to see it during the day, but at night it can be a good show looking from the east.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Storm Struck »

That is true Tim but i would say for the season and location would make the heating factor abit different to Canterbury east of the Foothills.
In Tuesdays case it was a developing NWer with rain building on the west coast, the fohn affect does start from the eastern side of the Alps but there wouldnt be suffient enough heating at this time of year through the high country.
Perhaps Richard could comment on how the temperature was during the day, i would think with all the snow around and cloud cover beforehand there wouldnt be much time for heating up that way.
Once the NWer spills over the Plains i think especially during winter/spring is when the wind warms up abit more.
Another thing we have to take into note is how the thunderstorms managed to spill so far east of the alps, as this doesnt happen that often.
The last time i recall a thunderstorm spilling eastwards here was back in 1998 and it was a night time storm, very different type of storm again with very loud ground rumbling thunder.
I remember that night clearly, and the rain was just torrential.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Richard »

Thanks guys for ya ideas,but none yet has explained why.I'll describe in more detail how Tuesday nights storm unfolded,there were ten bright flashes,not the usual over the maintains flashes,these were close which sent me running outside for a better look.The early 2 to 3 flashes had about an 8sec gape between the lightning and thunder,it was raining so i couldn't see the lightning but the sky lit up and looked to have been to the south.There was about 4 min gape between flashes during the whole period.It wasn't till we got to the fifth and sixth flashes that i was able to see the lighting for the first time,as i indicated previously this was sleet lightning and these shot across directly over head from the west to at least 15km to the SE and around to the NE,the last of the flashes were to the north.A similar event last summer that lasted three and half hours all sheet lightning and mostly over the Amuri Plains.Because most of this type lightning is happening over this area it would be very much seen and heard in the daylight hours.
In this thread dihttp://www.weatherforum.org.nz/phpBB3/viewtopic.php?f=2&t=3661 drew posted the NZ map of the strikes on that night,i can only see two strikes,both in maintains west of here,so that sheet lighting had to have traveled a long way from where it was earthing out.I also can certainly rule out any thermal influence at this time of year,its a completely different weather system
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Re: Amuri area's northwestly Sheet lightning

Unread post by spwill »

Because most of this type lightning is happening over this area it would be very much seen and heard in the daylight hours.
just conincidence that these storms(active trough/front) have crossed your location at night rather than daytime. Not sure where Amuri is but if it is east of the main High Country the local thunder will have been from high level lightning in old Cb tops that have drifted east.
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Re: Amuri area's northwestly Sheet lightning

Unread post by NZstorm »

spwill wrote
will have been from high level lightning in old Cb tops that have drifted east.
Agree, the storm at Amuri was some spillover activity getting across the devide from the West Coast.


Richard wrote
I also can certainly rule out any thermal influence at this time of year,
Yes surface heating doesn't factor in these storms at any time of year. Orographic lift on the West Coast/frontal lift are the trigger.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Myself »

Tornado Tim wrote: From my understanding If the day has been sunny the land temperature will be allot warmer and when it hits nightfall the warmth from the ground the start to warm the cooler air just above the ground and then cause that to rise.
As the warm air rises cooler air will replace it and start to warm up as well, this may very well help the formation of thunderstorms if a body of cold air shift on top of the warm air below, such as a cold front.
This never really happens to help storms because of a) mixing and b) air is very poor conductor of heat.
Ground warmth from the day dissipates very quickly after sunset, but not much of this goes into warming up the lowest surface air (because air is rubbish at conduction). However, assuming it does, the process you describe would still not occur to such an extent because of conventional mixing, and also the breakdown of the hypothetical "parcel" theory.
There are still vertical circulations of air at night, but they are not enough to contribute to any genuine instability, and also there is the likelihood of a cap to break.
Even on a stinking hot day, if you had a sounding with a very large superadiabatic surface layer, it might look unstable as hell...but it would not be a realistic representation of any useful instability, again because it would likely get mixed out.
"if a body of cold air shift on top of the warm air below, such as a cold front" - a cold front tends to surge ahead at the surface with the colder air at higher levels lagging behind.
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Re: Amuri area's northwestly Sheet lightning

Unread post by rawdon »

Hi Myself !! What is your background re meteorology if you dont mind me asking..

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Re: Amuri area's northwestly Sheet lightning

Unread post by Richard »

Steven, i very much agree with you in that it is defentily spill over activity from the West Coast. But as spwill pointed out, commonsense would tell ya that it should be close to a 50/50,day-night occurrence and that its purely a coincidence that these weather systems have come through at night,but to me i feel now its gone past being a coincidence,its happened just to many times at night now to be a coincidence. Tornado Tim at the time of these events there were strong NW winds so any thermal convection can be ruled out as the air had only just desended from over the maintains.My thinking is that these storm clouds that have made it over to this side of the maintain still have of a electrical charge left in them to create this horizontal lightning,would the sun have a influence some how???its certainly got me thinking
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Re: Amuri area's northwestly Sheet lightning

Unread post by Tornado Tim »

Edit: Just letting off a little steam.
Last edited by Tornado Tim on Sat 25/07/2009 18:49, edited 1 time in total.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Storm Struck »

Come on guys people have differing opinions and are entilted to use them wisly.
Does anyone have a map ( Satelite or isobaric ) for last winter when a thunderstorm crossed the Alps and spilt eastwards through Christchurch bringing a dramatic thunderstorm with heavy hail?.
It would be interesting to see if Tuesdays matches up with it, i only say that because a thunderstorm did cross into eastern North Otago/South Canterbury and i believe the SWer was coming up at the same time.
Simular thing to what happend in Christchurch last year.
I noticed the isobaric flow was more W-SW but with the greater majority of the rainband activity on the West Coast and Southland, but however still managed to spill heavy showers eastwards along with the thunderstorm in North Otago.
I would think if it was more N-NW the activity would stay west of the Foothills, depending on how much activity was on the West Coast and through the Alps.
Could be worth keeping note of so in the future we can get close to predicting the sneaky Alps storms.
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Re: Amuri area's northwestly Sheet lightning

Unread post by spwill »

Tornado Tim wrote:
From my understanding If the day has been sunny the land temperature will be allot warmer and when it hits nightfall the warmth from the ground the start to warm the cooler air just above the ground and then cause that to rise.
As the warm air rises cooler air will replace it and start to warm up as well, this may very well help the formation of thunderstorms if a body of cold air shift on top of the warm air below, such as a cold front.
Not at this time of the year but during the warmer months upper level cooling over a warmed surface can trigger showers after sunset particularly in the north of NZ where higher dewpoints retain heat better.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Tornado Tim »

spwill wrote: Not at this time of the year but during the warmer months upper level cooling over a warmed surface can trigger showers after sunset particularly in the north of NZ where higher dewpoints retain heat better.
Thats what I thought,
Hence why I used the term may help "assist" to avoid the backlash.
I completely forgot about the time of year.
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Re: Amuri area's northwestly Sheet lightning

Unread post by NZstorm »

The thunderstorms coming off the divide in a NW scenario are elevated and are thermodynamically cut off from the the low level airmass east of the alps. Thus there is no enhancement from thermals that may exist over Canterbury.

The storm over coastal north Otago/SC on Tuesday night looked to have been triggered by convergence between a SE change on the front and the NW'er.


Jason wrote
last winter when a thunderstorm crossed the Alps and spilt eastwards through Christchurch
It would be interesting to know the date.
Last edited by NZstorm on Sat 25/07/2009 19:27, edited 1 time in total.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Dale »

Was there any kind of NE SE inflow to help kick them along a little.. many occasions this happened in the netherlands.. (note not europe) with diurnal heating and a bit of a kick from a seabreeze, forcing even the most mundane looking cloud to explode with lightning as it came off the great dividing range..
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Re: Amuri area's northwestly Sheet lightning

Unread post by Richard »

Dale are you referring to the storm that Jason just mentioned over North Otago/SC or what i experienced here in North Canterbury ???
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Re: Amuri area's northwestly Sheet lightning

Unread post by Dale »

I havent gone back through the archives for a specific storm, more putting my own experiences in aussie with them forming aft of the ranges, losing puff, moving over, catching onto another trigger in this case a mix down of the atmosphere or seabreeze convergance influence.. in then explosive case, triple point convergance scenario.. the topography of the south island would enhance storms in a similar situation, i am not a forecaster nor do i pretend to be but there are quite a few similaritys down there which i would tick off the list first. What Steven had also touched on above.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Richard »

Going by the latest satellite images theres a line of thunderstorms coming on to the north of the South Island,given it will arrive during darkness i expect theres a chance that there maybe some over head sheet lightning over this area ,hopefully.
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Re: Amuri area's northwestly Sheet lightning

Unread post by Richard »

No lightning was seen, even over the maintains,but still 11mm of some well needed rain instead
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Re: Amuri area's northwestly Sheet lightning

Unread post by Paul Mallinson »

Hi Guys,

Interesting discussion. I think NZstorm is on to it. I think what is happening (without having seen the particular situations being talked about) is you have a front moving up over the South Island that has thunderstorms triggering on it. These are often elevated and kicked off in many cases by the lift over the terrain. Often you have very strong nw winds aloft and so there is a lot of shear and cirrus clouds (ice crystals) streaming across. We often observe a predominance of positive lightning over and down stream of the ranges and I think it is these discharges that are being seen.
Positive lightning is known to originate high up in CB clouds, up in the anvil/cirrus areas. These discharges are characterised by mostly single huge discharges with very high voltages (to overcome the potential difference bewteen high up in the cloud and the ground). Consequently they have massive amperages (in the order of 100 to 300 kiloamps) and are known to be able to travel a long way laterally as they come to earth - I believe up to 6 times the distance from the origin as they are high up in the cloud. It is these strikes that often start forest fires in North America because they often come down in an area away from the rainshower. The big amperage helps to start fires.
So maybe it is the flash seen from these lightning strokes that is being seen. I think also the reason they seem to only occur at night is because they are most easily seen then. In the daytime, they would be hard to see unless one came down near you.

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Re: Amuri area's northwestly Sheet lightning

Unread post by NZstorm »

Looking like there could be spillover ts activity today over the upper South Island given the upper air will cool off this afternoon while lots of moisture is brought down onto Westland/Buller by very strong NW flow.
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Re: Amuri area's northwestly Sheet lightning

Unread post by spwill »

Paul wrote,
I believe up to 6 times the distance from the origin as they are high up in the cloud. It is these strikes that often start forest fires in North America because they often come down in an area away from the rainshower. The big amperage helps to start fires.
Good information Paul.

I can recall in Navada seeing cloud to ground lightning out of small cb with not much rainfall evident, just some virga, so dry thunderstorms. I think the low humidity and high temps ( summer) of this region evaporate alot of the rain before it can reach the ground.
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