Topic: Dry line/tornadic storms in the NT

[Mike]

 This question is perhaps aimed at anyone who has a knowledge of tornadic dry line storms.  Here in the NT I have found no data on dry line storms of the tornadic/supercell kind (cyclone borne supercells excluded).

 (1)  The definition of true tornadic dry line storms in Australian conditions.
 (2)   If the NT is separated by desert and tropics does that constitute a 'dry line'?
 (3)   Has anyone seen any recorded data on supercells in the NT from non monsoonal troughs/lows/cyclones?

 I would like as much info as I can get from those who know from experience what an actual dry line storm is.  As far as what I've been told, we have tropical storms in Darwin, but what do places way down the track below the tropic line get?

Mike

[Jimmy Deguara]

Mike,

I recall you had suggested in a previous thread the term "dryline" and I guess you were referring to Gulf Lines in the Darwin region.

The definition of dryline refers to a change in moisture over a specified distance see definitions below:

http://en.mimi.hu/meteorology/dry_line.html

So basically it is a boundary where there is a marked change in moisture as one traverses across the boundary. Such boundaries are not uncommon across the planet. It should not be confused with trough lines which are marked by changes in pressure / pressure gradients.

The dryline behaviour is one that requires some research to fully understand. In the US basically in the western Texas bordering with New Mexico, a semi-permanent dryline persists often for months and progresses back and forth with diurnal heating and nocturnal cooling - similar to the beahviour a sea breeze goes through.

Regards,

Jimmy Deguara

[Mike]

Yeah I remember the comment - !

Interesting, Jimmy.  So would large storms developing in Katherine 300km south of Darwin with dew points in the low to mid teens be classified as dry line even though this location is still within the tropics and there was no trough line ?   

When is a dry line a 'dry line' as far as tropical locations go or more to the point, is it a layman's view that any boundary with significant dew point changes etc on either side be classified as dry line ? 

Storms closer to Darwin don't get going with low dew points during the day, nighttime it's a little different - which is why i'm confused as to what I could consider dry line storms if i had to discuss the subject with anyone who asks given my location!

All the online things I've read all revert to one place - the USA.  They all say that dry line storms are the most violent on the planet and form on the plains, supercellular and the like - nowhere does any online resource mention dry lines storms here - hence my questions!

I want to be absolutely sure that the term dry line is not over emphasised as far as the tropics go in conversation re the NT, sure you get storms on a dry line - but pure 'dry line' and those beasties forever mentioned in the US...

That's my dilema.


Mike

[Michael Bath]

One thing to consider with the US dry lines is the temperature and shear profile that accompanies those boundaries.  You will get 'dry lines' here and other places on the planet but the other ingredients will rarely be in place to result in tornadic supercells.

[Mike]

That was my thinking all along.  It's the specific conditions to support the storms that are missing.  It's okay to have shear but without helicity values up and all the rest of it they just don't occur and if they do they'd only be regarded as a big storm by someone without knowledge of such things!  There are those that won't be convinced I'm afraid no matter what facts are thrown at them!

[Jimmy Deguara]

Mike,

Seems like you have been conversing on another forum where a few exist with the dillusional concept that Australia deserves a silver medal when it comes to tornado density or occurrences. I personally do not bother to convince the unconvincing. Convincing a wall is sometimes easier.

Michael, you hit the nail on the head in regards to shear as well as other factors when it comes to the importance of drylines and their impact on tornadic development. If course to be fair by definition, tornado in the form of landspouts certainly do occur along boundaries in Australia where convective cloud coincide with extreme surface based lapse rates. However, when it comes to supercells, I think even non-tornadic supercells would be a rare occurrence in the Northern Territory (let alone tornadic).

Regards,

Jimmy Deguara

[Mike]

 Yes you're perception was right.  It was in response to a quite sensible post re the question of tornadic supercells in the NT.  Unfortunately my wisdom of such things fell on deaf ears once more. No amount of convincing - even with Tim Marshall's article - made a difference.  I know I'm right re this one and the replies here echo the same given the supercell observations of those on this forum.  This argument will never be resolved on that particular forum - unless one individual can be convinced otherwise - how sweet that would be!  it would be almost as satisfying as winning Lotto!

As i mentioned, I've found nothing to correlate this topic to the NT.  I searched high and low and even though this particular individual said he had chased large dry line supercellular type storms I've been unable to convince   the person to post data, photos, soundings, radar images - anything for the benefit of other members wanting to see such details.  I think that says a lot perhaps for reliability.

Thanks for the positive input, it's been a great help.

Mike