Mammatus?

Fujita Phil · Unread post by **Fujita Phil** » Fri 05/12/2003 15:55

So I'm just waiting for the onset of possible severe gales

arriving late this afternoon and the clouds over Dunedin at 3pm, I would describe as Mammatus.

I was under the impression (my own thoughts) that these clouds usually preceded a front and the clouds were actually "distorted" by very strong winds at that level. Usually the weather arriving after these clouds will be very warm strong westerly winds with a southern change later. (Well what Dunedin person doesn't know that if we have a warm windy day, it will probably rain the next

)

Most definitions of Mammatus state that these clouds often form under the anvil of weakening thunderstorms, though I couldn't agree that there were thunderstorm clouds overhead in Dunedin today.

Is this true? Or is it just the cooler air above sinking into the warmer air below without any high winds?

NZstorm · Unread post by **NZstorm** » Fri 05/12/2003 17:21

Hi Phil,

Rather than sinking air, I would say sinking ice crystals.

The mamma you are observing in Dunedin is likely to be Altocumulus mammatus. It has no association with Cumulonimbus as you suggest.
It forms on frontal Altocumulus in a NW flow.

Cumulonimbus mammatus occurs on the weakening part of a Cumulonimbus or Thunderstorm.

NZ Thunderstorm Soc · Fri 05/12/2003 17:55

Great NW Arch day in Canterbury today. On the way to work this morning around 7:45am. I did notice some mammatus form in the Arch cloud.
Warm day here too. The thermometer not quite touching 30C.
26.5 down the road at a friends place, but I don't know what the official temp was yet but Micheal would of enjoyed the day

JohnGaul
NZTS

Fujita Phil · Unread post by **Fujita Phil** » Fri 05/12/2003 19:37

NZStorm wrote:Rather than sinking air, I would say sinking ice crystals.

Thanks Steven, just what I wanted out of this board...lots of knowledge.

NZ Thunderstorm Soc wrote:Warm day here too. The thermometer not quite touching 30C.

21.8C here at the moment, 32% humidity and the winds are starting to pick-up.

tich · Unread post by **tich** » Fri 05/12/2003 21:06

21.8C here at the moment, 32% humidity and the winds are starting to pick-up.

The northwesterly has freshened at times today in Chch, but it's a bit lighter now. A northwest arch developed this afternoon - I could see rain falling from the back of it, probably over the foothills. (whether it reached the ground is another matter) About 20C in the central city.

NZstorm · Unread post by **NZstorm** » Fri 05/12/2003 21:14

I suggest mammatus is a form of precipitation (virga).

That front over the SI looks quite active this evening . The K index at Invercargill is 26 which suggests alpine thunder with the front.

Dean. · Unread post by **Dean.** » Fri 05/12/2003 22:04

Northwest arch over Mid Canterbury as the sun was setting this evening,looking like its getting ready to blow overnight.
Cooler than Christchurch here today with high overcast conditions all day,temperature 23 degrees.

NZ Thunderstorm Soc · Sat 06/12/2003 17:58

NZstorm wrote:
That front over the SI looks quite active this evening . The K index at Invercargill is 26 which suggests alpine thunder with the front.

I thought the front was quite useless, rather than active. It may of produced the rain with possible thunderstorm down south but it was fairly useless here.
I recorded a mild night here (17C minimum)to 8am with no evidence of any southerly coming through which was forecasted. Mild morning with the frontal high cloud moving away and becoming fine and clear from 1pm when I finished work. I noticed there was a NE, when it should of been southerly. Because of this, it clouded up in the afternoon with very weak convective cloud formation to my disappointment.
No 'Immmmph" to produce anything exciting. Never mind better luck next time. More boring weather for Christchurch coming up next week

JohnGaul
NZTS

Manukau heads obs · Sun 07/12/2003 10:59

becuase "the legs have been chopped off" the cb's as they cross the mountain ranges, you still see the top part of the original CB in the eastern areas, and so yes you will still see the mamatus of a CB too...

thats what I saw in the 3 months i spend just inland from mosgiel...
just my thoughts

low cloud and drizzle here from the remanins off the font

the low in the north tasman: it will be good to get the rain being a dairy farmer:
farming is still the main export earner off this country (but farmers are at the bottom of the heap, and get a trickle off the cash that is left after evryone else has creamed it!