NZ Weather Forum

I also agree with NZStorm and Aaron, looking at the Radar Images and Photographs it looks like a linear type storm system.

Steven reported very strong wind, which is typical of a linear storm system and organised outflow.
Even though this storm wouldn't be classified as Supercell, this doesn't mean there wouldn't have been smaller rotations in the cloud or funnel clouds.
The southerly buster storm more or less was a front to the southerly front , the flow prior to this front was NE from what I understand. The southerly would certainly interacted with the NE flow when moving through and would account for any reported spin up in clouds etc.

I archived the metservice hourly Canterbury radar images from 3 until 11pm yesterday, after I happened upon that huge spiral in the allnz at 9pm. Also led me to hunt down this forum/thread. Might have had something to do with radar range, but looks like it died out pretty quickly past there. Can't brain some hosting so, sweet to attach em right? I could but the whole lot up if someone wants to see.

Very nice pics here, I'm so jelly.

Metservice indicated 3cm hail with this storm, I presumed looking at the radar at thetime that this was over the coast. Everytime we have had hail this big its been associated with a storm that is beleived to be a supercell from what ive seen.

Im sure I saw the radar hit >60 dbz yesterday offshore

Tornado Tim wrote:I also agree with NZStorm and Aaron, looking at the Radar Images and Photographs it looks like a linear type storm system.

Steven reported very strong wind, which is typical of a linear storm system and organised outflow.
Even though this storm wouldn't be classified as Supercell, this doesn't mean there wouldn't have been smaller rotations in the cloud or funnel clouds.
The southerly buster storm more or less was a front to the southerly front , the flow prior to this front was NE from what I understand. The southerly would certainly interacted with the NE flow when moving through and would account for any reported spin up in clouds etc.

Agree 100%.

03Stormchaser wrote:Metservice indicated 3cm hail with this storm, I presumed looking at the radar at thetime that this was over the coast. Everytime we have had hail this big its been associated with a storm that is beleived to be a supercell from what ive seen.

An embedded stronger updraught could have produced hail upto 3cm given the lapse rates were quite steep. You are better though to have visual obs of hail rather than radar based to be sure how big hail is.

Nev wrote:Stuff has a nice video of a 'Funnel cloud over Whanganui' at about 8am this morn (from facebook).

8am in the morning is not the usual time to see a funnel cloud, good clip.

Timelapse from Wednesday - best viewed in HD in a dark room

Really enjoyed that Steven!

Glad you enjoyed it - the result was better than I'd expected... After skimming through it a couple of times I counted 28 separate lightning bolts and at least a dozen flashes in the cloud. Towards the end, the lightning was almost overhead so with the approaching wind and rain it seemed like a good idea to stop filming

Between the rain and using an ND filter the lightning isn't very bright e.g.

My chase video is up. Features at the start what we think was a weak meso passing over, problem was my camera just isn't wide enough to capture it all. I think that's were my new Go Pro will come in handy. What I'm pretty sure is a large funnel (although you can hear mike calling it a wall cloud and me agreeing lol) Not a lot of lightning but you do hear the near continuous thunder

Thanks Steve, good clip . No sure about funnel clouds there. A good wind convergence line, there was an agressive Southerly up against a NE wind.

Nice vid!! love the thunder aswel!! love the sound of it.

Great capture, sound of the thunder is neat. Hopefully the storms make it to Christchurch next time

He is a photo of what ever it was, taken by Tilly.

Considering the amount of rotation it had I thought it was a funnel.

spwill wrote:No sure about funnel clouds there

I tend to agree with you in regards to what is seen in Steven B's footage. But there was broader cloud base rotation because of the NE sliding into the Southerly. I doubt this rotation would have extended to 800mb.

Steven G's time-lapse shows some small cloud rotations (especially in the later half) on the leading edge of the gust front. Notice how gust front (mesoscale cold front) was neatly tucked away underneath, causing the warm pre-frontal air to rise. I would account that due to the swift southerly surge.
Storm's such as this make gust fronts quite quickly in the initiation stages, and actually help to keep the storm going. (It seems a bit of a counter argument, but there is a reason for this).

Not all Cold fronts are equal..... Some have much more of a resistance when moving through. Simply put the resistance of a cold front is determined by the placement of warm and cold air.
If the cold air more less acts like a "wall" then then there is much less interaction between the cold and warm air as the warm air will simply glide over the top of the cold.
However in some circumstances the cold can extend from 2/3 the height of the a standard cold front. Where the absence is contained at the SFC. So more or less in this situation a pocket of warm air undercuts a section of a cold front at the SFC. Since cold and warm air dont like mixing there is a allot of "friction" and that's what can lead to some severe weather phenomena as the two air masses are more or less at battle with each other,plus there was the NE shearing effect that played into part.
In this case, Storms formed on the leading edge of the cold front. As the storms formed, gust fronts developed (smaller scale cold fronts called mesoscale cold fronts).

Since the gust front extended beyond the initial cold front, it created more resistance when the front moved through. The storms outflow (air contained in the gust front) was still warmer the main cold front behind. So air was drawn in 2 areas.
On the main cold front and just before the gust front (As shown in Steven G video).
The updraft on the main cold front would have been much less vigorous than on the pre gust front. The reason for this is relatively simple, the temperature differentiation between the main cold front and air that had been affected by the outflow would have been much less than the mesoscale cold front and the warm pre frontal air.

My apologies for the length of this post, Once I start writing something I feel like I need to explain it and one thing leads to another etc....

Strands of cloud form in the turbulent lifting air on the frontal line and it is very easy to mistake them for funnel clouds.

To note the rotation in the cloud bases occurred on the left side of the CB where the windchange occurred and was generally much drier with the core of the cell to the right, this similar sort of thing happened on the Monday 16th December with the supercell storm that dropped golf ball hail over Mayfeild.
The drier line produced the rotation but also the tornado that touched the ground me and Mike witnessed, along with several funnel clouds.
To note some of this rotation could have had topographical ramping up from the nearby valleys and foothills .
I think it can be still classed as funnel clouds provided the column is existing for even short periods of time and showing forms of clear rotation.