Heavy Showers/Thunderstorms 26th-2nd

tgsnoopy · Unread post by **tgsnoopy** » Tue 31/01/2006 07:08

Foggy Hamilton wrote:If this cloud clears it may turn very interesting with severe tstorms forecast in the afternoon, hopefully.

That would figure, the day we go back to work

NZstorm · Unread post by **NZstorm** » Tue 31/01/2006 08:02

It sure looked like it would be an active band going into it, but no lightning was observed.

Yes, a few heavy showers from cu tops of 4500m yesterday afternoon over central NI. A slot of stable air in the middle atmos prevented a bigger cb forming. Shows up on NZWP1200 sounding.

A similar day today. A few heavy heavy showers developing, particularly inland. Low risk of thunder if there is lots of surface heating/convergence.

spwill · Unread post by **spwill** » Tue 31/01/2006 08:14

Got about 3 hours sleep out of that one.. dipping to just 19.6c
Temps are 19-21c across the North Island at the moment.

The TV ONE weather forecasters last night had a forecast overnight low temp for Auckland of 16C when dewpoints in Auckland have been stuck near 19C for the past few days.

Our low was 20C.

RWood · Unread post by **RWood** » Tue 31/01/2006 08:32

tgsnoopy wrote:I drove from Tauranga through Rotorua, Murapara, Lake Waikaremoana, Wairoa, Napier, Taupo, Rotorua and back to Tauranga this afternoon. The 95km of gravel was the worst corrogated I've ever seen it, and loaded with idiots driving on the wrong side of the road trying to hit me head on. Bad idea driving on SH38 in that direction on the last day of a holiday weekend.

That's why I like driving in the SI - most of the people are missing! With the cretins one encounters on the road these days, you're welcome to the traffic density in the northern zones...

Gary Roberts · Unread post by **Gary Roberts** » Tue 31/01/2006 08:38

RWood wrote:...I like driving in the SI - most of the people are missing! With the cretins one encounters on the road these days, you're welcome to the traffic density in the northern zones...

Hey, wait'll you see my driving...you'll wish you were in a Remuera traffic-jam! I'm infamous as one of the World's worst drivers!

squid · Unread post by **squid** » Tue 31/01/2006 09:33

Interesting forcast for the upper NI hope it comes together

Valid to: 12:00 am 1 Feb 2006 NZDT
Issued at: 9:19 am 31 Jan 2006 NZDT

The main ingredients for thunderstorms: very warm temperatures, high moisture and areas of fairly strong low level wind convergence, are expected to come together this afternoon over the North Island. A few severe thunderstorms may form towards the west coast of Northland this afternoon as sea breezes blow onshore for a time. These sea breezes are likely to weaken by evening,carrying the thunderstorm risk offshore.

Further south, from Waikato to the central high country and to the Hawkes Bay area south of about Napier,there is a moderate risk of severe thunderstorms forming by late afternoon.These storms,and those in Northland,have the potential to deliver rainfalls of up to 40mm in an hour or less time, and could cause local flash flooding. In a surrounding envelope the risk of thunderstorms is similar,but these would probably not give rainfall accumulations as high and are more likely in the afternoon than the evening.

Paul Mallinson · Unread post by **Paul Mallinson** » Tue 31/01/2006 11:01

tgsnoopy wrote:I drove from Tauranga through Rotorua, Murapara, Lake Waikaremoana, Wairoa, Napier, Taupo, Rotorua and back to Tauranga this afternoon. The 95km of gravel was the worst corrogated I've ever seen it, and loaded with idiots driving on the wrong side of the road trying to hit me head on. Bad idea driving on SH38 in that direction on the last day of a holiday weekend.

There was a light mist falling as I left Tauranga which stopped not far out of Tauranga. The fog lifted close to Ngongotaha going into Rotorua. Otherwise the rest of the trip was fine... Except for a torrential downpour on the Rangitaiki straights going into Taupo about 7.30pm. It sure looked like it would be an active band going into it, but no lightning was observed.

It's horribly humid/hot this evening (22.8Â°C 81%), I'm looking forward to an end to these stinking hot nights.

Where's our Electrical storms? This is the worst year for them that I can remember.

Interesting report tgsnoopy, especially about the torrential downpour. I have noticed that there were very few lightning strikes with the Taupo downpour on Saturday evening and the severe storm that occurred in inland eastern Taranaki on Sunday evening. This I think is due to the very warm temperatures aloft. The instability allows heavy showers to form but to get the lightning, the precip and updrafts have to travel up through from the zero mark to about -20+C to get charge separation. So only the very tallest cells will generate some lightning. In the case of last evening. I think the cells were tall enough for very heavy showers, but hadn't gone high enough into a cold enough environment. The Wellington radar showed decent precip tops to about 6 to 7kms which was probably somewhere near -10C.

So we have the dilemma of calling these things thunderstorms when they may only produce heavy showers. That's why the thunderstorm charts are headed up Severe Convection/Thunderstorm Outlook. It looks like the forecast soundings for today will go up thru a deeper layer with several degrees of cooling aloft expected. We'll see!.

Paul

Paul Mallinson · Unread post by **Paul Mallinson** » Tue 31/01/2006 11:31

tgsnoopy wrote: was fine... Except for a torrential downpour on the Rangitaiki straights going into Taupo about 7.30pm. It sure looked like it would be an active band going into it, but no lightning was observed.

Tgsnoopy
Would you care to hazard a guess what an hourly rainfall might have been if you were slow moving under it?

Sat pics show a west to east cluster of convection in the area you say you drove through with cloud top temps about -27C.

Paul

Willoughby · Unread post by **Willoughby** » Tue 31/01/2006 16:18

I see Napier Ap is on 33c/19c.. Phew!

Darkening skies here with Cu tops to 4-5000m.. showers not too far away hopefully

NZstorm · Unread post by **NZstorm** » Tue 31/01/2006 16:42

Darkening skies here with Cu tops to 4-5000m.. showers not too far away hopefully

Those cu tops are more like 4-5000feet foggy. I get a good view into the Waikato from my vahranda in Grey Lynn. In a scale of 1 to 10 for convective activity today, it looks like about a 1 so far.

Midday sounding did look on the unstable side so something could still fire.

Can see distant cb tops out to NW.

Manukau heads obs · Tue 31/01/2006 16:50

However, can see distant cb tops out to NW.

are you sure thats not part of the bereclinic leaf that has developed as TC Jim has got closer?

but the rain radar does show showers way out to our NW and west
i will get a better view when i go to milk cows at the farm that is 700 feet straight above the tasman in the next 30 minutes, LOL

i see those shower tops do show on the sat image...
i wonder if they will move closer...
the upper level cloud is moving down from the nnw ....
maybe this bereclinic leaf and trough to our north will keep moving south and we will get rain that is forecasted?
maybe not?
i have seen where TC's to our north like that can suddenly bring on instability and late afternoon thunderstorms can suddenly develop....i remember ightning striking an electic fence and starting a fire in some long grass once from just a situation...by the time the local fire force got there (which i was part of) a hail shower put out the fire!

edit
i see the met service have a now cast out for fine spells and a few thunderstorms developing
a change in tune ....i think they have learnt a bit from the last time in dec...

squid · Unread post by **squid** » Tue 31/01/2006 17:09

what is a bereclinic leaf ????

GraemeWi · Unread post by **GraemeWi** » Tue 31/01/2006 17:21

I can see some distant cb tops out to my NW as well - they look to be a long way out to sea... maybe we will get something in a couple of hours?

spwill · Unread post by **spwill** » Tue 31/01/2006 17:43

Those cu tops are more like 4-5000feet foggy. I get a good view into the Waikato from my vahranda in Grey Lynn. In a scale of 1 to 10 for convective activity today, it looks like about a 1 so far.

Cu over the Kaimai's from Auckland using some zoom on my Camera.

NZ Thunderstorm Soc · Tue 31/01/2006 19:35

squid wrote:what is a bereclinic leaf ????

Augie Auer used to go on about these before he was taken off TV3's weather. They are are an outsourge from a forth coming weather system which if moving towards the South Island could produce good rainfalls which would fill uip the lakes and there would be no power shortages

With his accent, I thought he used to say "Leap" which probably made sense as this could be a system leaping out of an on coming low or trough

JohnGaul
NZTS

GraemeWi · Unread post by **GraemeWi** » Tue 31/01/2006 20:23

Just on sunset here - a heap of Castellanus has popped up - too late in the day?

spwill · Unread post by **spwill** » Tue 31/01/2006 20:44

Apart from some Cu (non shower) over the distant Kaimai's, the day has been convectively dead. Too much cloud today for sufficient heating to produce showers.

May get some rain or showers here overnight drifting down from the North.

Manukau heads obs · Tue 31/01/2006 22:01

May get some rain or showers here overnight drifting down from the North.

yes...if a new upper level low/trough develops
OR
the whole cloud sheet gets pushed away to the SE by that incoming front from the SW and it will be fine tomorrow...

the forecast for today was off the mark, never mind....
maybe they should say, there is a chance of thunderstorms if the morning cloud burns off...

squid · Unread post by **squid** » Tue 31/01/2006 22:32

ty for explaining that to me there is some very heavy rain in the far north atm looking at the 10pm radar

NZ Thunderstorm Soc · Tue 31/01/2006 22:37

Small band of thunderstorms over/off Marborough heading towards Wellington according to the 10pm radar and the lightning detector.
Can you see these off in the distance, Jase/Tony, or is the Kaikoura peninsula in the way

JohnGaul
NZTS

spwill · Unread post by **spwill** » Tue 31/01/2006 22:49

Atlast a Thunderstorm, North of Kaikoura.

Storm Struck · Unread post by **Storm Struck** » Tue 31/01/2006 22:50

Way too farr up the coast John looks like it's around Blenhiem there by the radar certainly a small storm there looks like it has formed from that upper level high cloud from today.
I did notice at one stage today there was atually some cumulus within the high cloud this would explain the mamatus too.
Yes SPwill I didn't think it was but I thought id gt others opinions as well.
This shows that a weak change such as this can produce a thunderstorm.

.
What number you got out for Friday John not looking too bad for thunder at this stage.
Cheers
Jason.

tgsnoopy · Unread post by **tgsnoopy** » Tue 31/01/2006 22:54

Paul Mallinson wrote:
tgsnoopy wrote: was fine... Except for a torrential downpour on the Rangitaiki straights going into Taupo about 7.30pm. It sure looked like it would be an active band going into it, but no lightning was observed.
Tgsnoopy
Would you care to hazard a guess what an hourly rainfall might have been if you were slow moving under it?

Sat pics show a west to east cluster of convection in the area you say you drove through with cloud top temps about -27C.

Paul

In the order of 100mm/hr rate if consistant, it was pretty darn heavy. I use Rain-X on my windscreen and had to slow to about 70km/hr, not due to visibility but due to aquaplaning. There were a couple of vehicles that had aquaplaned off the road (no one hurt that I could see, and they already had people offering assistance).

Paul Mallinson · Unread post by **Paul Mallinson** » Wed 01/02/2006 10:25

tgsnoopy wrote:
Paul Mallinson wrote: Tgsnoopy
Would you care to hazard a guess what an hourly rainfall might have been if you were slow moving under it?

Sat pics show a west to east cluster of convection in the area you say you drove through with cloud top temps about -27C.

Paul
Thanks for that.

Paul
In the order of 100mm/hr rate if consistant, it was pretty darn heavy. I use Rain-X on my windscreen and had to slow to about 70km/hr, not due to visibility but due to aquaplaning. There were a couple of vehicles that had aquaplaned off the road (no one hurt that I could see, and they already had people offering assistance).

Willoughby · Unread post by **Willoughby** » Wed 01/02/2006 11:26

Heavy rain this morning from 5am to end January.. got 7.4mm total

Now 24c/21c and overcast.. will probably see a few heavy showers develop today, though the rain radar has the precip dissipating a lot..