Convective period. 26-28 Nov

David · Unread post by **David** » Tue 26/11/2013 19:03

jamie wrote:We were slightly too far west this time. Missed out today so desperate to catch something in the next two days or we will be looking quite sad with only 46mm this month and only 75mm for October. We need 100mm/month to stay in good condition.

I know how you feel! We have quite a big garden and I've had to do some watering most days. Once one watering cycle finishes, the part watered at the start of the cycle is ready for more...

We are a bit drier than your area, we have only had 34mm this month after 24mm in October.

I have a job interview in the city Thursday 10am, so I hope there isn't a thunderstorm at that time. I think I would seem a little distracted maybe!

jamie · Unread post by **jamie** » Tue 26/11/2013 19:12

David wrote:I have a job interview in the city Thursday 10am, so I hope there isn't a thunderstorm at that time. I think I would seem a little distracted maybe!

Well things are looking good for tomorrow. They tick a lot of boxes for the BSCH's storm probability. Purple indicates "likely severe" over the kaipara area. Red is "possibly severe"

severe.png

Tornado Tim · Unread post by **Tornado Tim** » Tue 26/11/2013 20:44

Looks like there is a small low center with showers wrapping round it near Taupo. Its quite clear on the radar animation.

Steve B, us North Island guys will have to meetup before you go. Perhaps on Thursday chase day?.........
I saw some discussion on the White Island thread?..... Plans etc......

03Stormchaser · Unread post by **03Stormchaser** » Tue 26/11/2013 22:03

Tornado Tim wrote:Looks like there is a small low center with showers wrapping round it near Taupo. Its quite clear on the radar animation.

Steve B, us North Island guys will have to meetup before you go. Perhaps on Thursday chase day?.........
I saw some discussion on the White Island thread?..... Plans etc......

I don't arrive until Thursday night so sadly I am going to miss the action. I did look at changing flights etc but was just too expensive.

Manukau heads obs · Tue 26/11/2013 22:04

check out the latest thunderstorm outlook
I am in a good spot for tomorrow afternoon

jamie · Unread post by **jamie** » Tue 26/11/2013 22:21

yea i always thought tomorrow would be more western which puts me in a better position. Just hope something can develop and head this way

Tornado Tim · Unread post by **Tornado Tim** » Tue 26/11/2013 22:58

03Stormchaser wrote:
I don't arrive until Thursday night so sadly I am going to miss the action. I did look at changing flights etc but was just too expensive.

That doesn't matter so much, although its a shame you wont be here in time. Perhaps we can have a promptly arranged weather meet somewhere, when are you departing?

jamie wrote:yea i always thought tomorrow would be more western which puts me in a better position. Just hope something can develop and head this way

I can only hope that the Waikato doesnt get a prodominant NE, I am hoping for a Sea Breeze induced SE (which isn't in the forecast)

NE'rly's are terrible if they arn't Sea breeze induced here.

tgsnoopy · Unread post by **tgsnoopy** » Wed 27/11/2013 06:29

Tornado Tim wrote:Simon, Snoopsta... Are you guys keen?

Extremely busy, trying to free up Friday in light of conversations, but with two of my colleagues committed to a job in Rotovegas Friday I may not be able to. Have to see how it pans out. Sorry. Looking forward to White Island Sat... Anyone else joining us?

Manukau heads obs · Wed 27/11/2013 06:38

lots of blue sky down the western side here...and a light easterly...perfect for sea breeze convergence today

NZstorm · Unread post by **NZstorm** » Wed 27/11/2013 06:51

An issue with today's set up is the frontal cloud mass to our north looks like coming in today which will have a stabilising influence on our weather later today. GFS suggesting many areas will get good rain from it though. Just have to hope it holds back for a while.

tgsnoopy · Unread post by **tgsnoopy** » Wed 27/11/2013 06:51

Hang on, for some reason I was thinking Friday was the likely good day... But now I'm thinking Tomorrow looks a lot better... Which day was it you were all talking about?

NZstorm · Unread post by **NZstorm** » Wed 27/11/2013 07:28

I notice the Met Service have a weather warning up for tonights rain.

GFS showing the heaviest rain in the Bay of Plenty/Coromandel. Low level wind flows look weak though, so there won't be much orographic enhancement.

Manukau heads obs · Wed 27/11/2013 07:29

that jet stream cloud is getting a bit closer today, yes
but it was around yesterday too and the CB's developed underneath it OK

but yes that developing cloud sheet to the north and east is going to slide down onto the north island, wrapping in around the low to the west, overnight, tomorrow

GreggWard · Unread post by **GreggWard** » Wed 27/11/2013 07:47

Looking good for the Manawatu, tomorrow afternoon. I have the day off, so I hope this all pans out.

jamie · Unread post by **jamie** » Wed 27/11/2013 07:56

We had fog all night and this morning. Just clearing now. Very gentle variable breeze but currently from the SSE.

jamie · Unread post by **jamie** » Wed 27/11/2013 09:06

Outlook shows that today is very reliant in a western sea breeze getting going and by the looks if things they think the narrow part if te country will be less chance of that sea breeze getting going.

David · Unread post by **David** » Wed 27/11/2013 09:41

GFS suggesting only around 15mm for Auckland which is a little worrying - it's not going to do much given how dry the ground is.

David · Unread post by **David** » Wed 27/11/2013 10:36

Wow, only a low risk on Thursday despite low LI's and high CAPE. Wasn't expecting that

GreggWard · Unread post by **GreggWard** » Wed 27/11/2013 10:48

David wrote:Wow, only a low risk on Thursday despite low LI's and high CAPE. Wasn't expecting that

I saw that too David. I wonder why that is.

Manukau heads obs · Wed 27/11/2013 10:52

good signs of instability here now
been some good heating from the sun here...22C already
east wind is only light here, so should get a sea breeze hopefully
but the middle layer cloud is thickening up alot too

jamie · Unread post by **jamie** » Wed 27/11/2013 11:39

easterly just picking up here now. however we do have good heating and moisture with 23.2/17.6

Tornado Tim · Unread post by **Tornado Tim** » Wed 27/11/2013 11:52

GreggWard wrote:
David wrote:Wow, only a low risk on Thursday despite low LI's and high CAPE. Wasn't expecting that
I saw that too David. I wonder why that is.

Its because the upper air expected to be dry (likely to mix out, which what happened here yesterday) and the tropuspause is forecasted to be low, meaning the risk of getting lightning from any resulting convection is low.

There may be all the cape and LI in the world but if there if updrafts take in air and it subsequently dries out, the water vapour carries a much lower charge differentiation, which means the convection wont spark as well.

For a LT (Low Topped) Thunderstorm to occur the air needs at one point in the atmosphere needs to be saturated and the air needs to be boyant and carry a steep lapse rate(potentially even more than a normal Thunderstorm setup as there is less height for the Cb to carry a charge differentiation).
Often the saturation point can be achieved by the air meeting the Saturated Adiabatic Lapse point, however this doesn't mean it wont mix out afterwards. Also the more saturated the atmosphere is the more likely any resultant convection will give off latent heat (which then assists again in the lift/updraft process).

Hope that helps explains things.....

Michael · Unread post by **Michael** » Wed 27/11/2013 12:08

Just heard on radiolive,its a weatherbomb lol

Manukau heads obs · Wed 27/11/2013 12:21

the way the clouds are thickening up here, I suspect general rain will develop
.i.e the frontal band out to N and E will keep on propagating SW, wrapping around the low to the west

GreggWard · Unread post by **GreggWard** » Wed 27/11/2013 12:34

Tornado Tim wrote: Its because the upper air expected to be dry (likely to mix out, which what happened here yesterday) and the tropuspause is forecasted to be low, meaning the risk of getting lightning from any resulting convection is low.

There may be all the cape and LI in the world but if there if updrafts take in air and it subsequently dries out, the water vapour carries a much lower charge differentiation, which means the convection wont spark as well.

For a LT (Low Topped) Thunderstorm to occur the air needs at one point in the atmosphere needs to be saturated and the air needs to be boyant and carry a steep lapse rate(potentially even more than a normal Thunderstorm setup as there is less height for the Cb to carry a charge differentiation).
Often the saturation point can be achieved by the air meeting the Saturated Adiabatic Lapse point, however this doesn't mean it wont mix out afterwards. Also the more saturated the atmosphere is the more likely any resultant convection will give off latent heat (which then assists again in the lift/updraft process).

Hope that helps explains things.....

Thank you for the explanation Tim. Here I was, thinking with the low LI and high CAPE values showing for Manawatu, for tomorrow that it would probably be a good day for storms. I think I have a lot of learning to do.

How would I go about trying to understand all this? Do you have any good web page references etc?

Thanks

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