NASA studies the world's thunderstorms

[mikegeukes]

NASA studies the world's thunderstorms

Courtesy of: UPI
http://upi.com/NewsTrack/view.php?StoryID=20061026-084606-3560r

 

[Michael Thompson]

I have in the past posted a couple of messages regarding storms on MODIS pics in Argentina. CAPE can be very high at times, but shear is often lacking, especially towards Paraguay where activity picks up.

Compared to the USA mid west in May - June however, Argentina's spring ( now ) lacks consistency, although the last years in the USA may have some wondering otherwise.

 

[MJ Poore]

There's definately a distinction between types of large t-storms. The type you get over the Congo for example, which the article mentioned, are lo shear, and are just very large t-storms in a high cape environment, basically lots of warm humid air exploding. There's very little rotation involved.

I think supercells are a different business altogether, they are much rarer and need both high cape and high shear to get a persistant meso going. Supercells happen in environments where cold polar air and tropical air meet with warm air trapped below in an inversion, and where some kind of trigger, like a dryline is present to start the whole thing off.

Large tropical t-storms are as big as many supercells in many ways, but they don't behave in the same way. Totally different.

 

[Michael Thompson]

Hi PJ, I don't think anybody will argue with what you are saying.

In northern Argentina at present is 4000 CAPE and -6 LI, but no more than 15 knots from the 1000mb to 500mb plotted, although there is a steady direction shear from NE to NW.

However it is not always like that.

Some of the shear profiles I have seen in Bangladesh and NE India are healthy enough to use the S word.

 

[MJ Poore]

Indeed yes. I have heard a lot about about large supercells in Argentina and East India. It's an interesting subject, but hard to find info, except for the Bangladesh tornado site.

I'd like to understand a bit more about how supercells start in Australia, is it driven by fronts, drylines, etc. Not surprisingly it looks very similar to what we have on my side of the ocean? I've seen pics of big storms in Victoria, but I understand it's not common there for some reason, more common up north in the tablelands. Hope your spring storm season is kicking off. It's really got going over here in the past two weeks, although no big supercells as yet. Though we had a report of a 500m wide nado over the weekend during strong low level shear on some normal thunderstorms.


Mungo

 

[Michael Thompson]

Our problem with Supercells has been well discussed here before - lack of decent moisture and low level inflow. Too many times we get bone dry NW winds ahead of promising troughs. We do get pseudo dryline setups as often there is a NE moving boundary between the hot dry NW winds and moist NE winds.

Having said all that I think today may have been the first S word candidate in Eastern NSW.

See the radar animation below
We have to bear in mind that this is low resolution radar and that it is not best science to call too much on that - I would really like to see the doppler, but this is not freely available here.

The line was moving roughly east before the animation. The animation shows a split, with the south cell shifting to a more S direction. There also evidence of a wrap up into a HP.

On thr ground reports - powerlines down, extensive golf ball hail and damage.

There are some pictures in this thread, but unfortunately many taken of the hail on the ground rather than structure.

http://www.weatherzone.com.au/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=10;t=002110;p=3

In regard to South Africa, I guess if you were seeing these storms you are not in Cape Town. I look at MODIS everday for storms in SA and Namibia. There were some highly sheared storms in Namibia just a day or so ago.

Were was the tornado track?

 

[MJ Poore]

Nice animation. It's the southern cell that is the dominant, is that usual there? In SA it's always the northern most cell. I thought it was a S hemisphere thing? Maybe it have got to do with inflow?

Most of the tornadic storms or supercells here happen on the eastern side of the country - draw a straight line from Johannesburg to Durban - where there's a very active low level jet creating good shear, coming in either from the north or from east depending where you are. The problem we have is a lack of cold air and regular fronts.

Forgive my ignorance, is MODIS a satellite based system? The best realtime obs are on
http://metsys.weathersa.co.za
All the metars, radar and satellite realtime is there. They've even just installed a doppler in Botswana which might have picked up some of those storms you mentioned.

The tornado was about 40kms east of Pretoria.