Hi,
I live technically in the South Coast, it is borderline Shoalhaven river valley south of Braidwood, I got large hail here in Jan 06, I have seen funnels form etc. I am usually pretty accurate if there are storms around, I watch their build up and know when they move on and where they go to. They scare me to dead and I am fascinated at the same time. I have a few ideas about why and where they happen, that is one of the reasons I joined to find out more. Animals are very much in tune and one can tell a lot by observing them.
Focusing on severe storms. We discussed the conditions that favour severe thunderstorms in this thread
here.
In Australia, we can attempt to demarcate (if we must) the region where this favourable combination of 'ingredients co-exit most often by drawing a polygon, roughly from south of Sydney to Dubbo To Charleville to Noosa to Byron Bay and back to Sydney. Within this region, at the northern extreme, we are more likely to find good 0-6km windshear is most likely to be lacking and it seems that this region is usually on the wrong side (confluent, convergent) of meridional flow associated with the passage of amplified upper-level troughs. Further south, and also west, we find deep moisture to be the main issue. So armed with the knowledge of Australia's climatology we can easily see why eastern Australia south of the TOC is most ideal (and by extension, why we can conclude there is not great mystical Australian tornado alley somewhere way west of the divide) - again, as a general rule, we need instability, sufficient low-level moisture and sufficient wind shear through a deep layer of the atmosphere (ie sfc to 6km is often used) for intense, sustained thunderstorm updrafts. Looking at things more anecdotally, how many damaging hailstorms are in the historical record for Perth or Adelaide or even Melbourne? Now if you look at Sydney, supercell storms producing large hail are a pretty regular event, usually 1 or more times per year. Now, within this broad 'favourable' region there are factors that operate on a level below the broader synoptic setting scale - let's say micro-scale or mesoscale factors; meterologists can chime in now
Think about topography, coastline orientation, elevation etc. These can play a significant role in storm initiation and also intensification. There is now doubt that the Sydney basin favours storm intensification more often than not. Conversely, it seems that the abrupt coastal escarpment around Wollongong seems to inhibit storms that move in off the highlands - Michael Thompson could add his experience on the sea breeze inversion and other factors, so we should get him on the forum! The southern highlands is a pretty reliable storm machine but the moisture will generally be limiting until end of spring early summer, and sometimes indeed for the whole season.
Many chasers would regard the northern rivers as the most reliable place to chase in eastern Australia, esp. after this season as is stands. I am of the oppinion, as a chaser, that things rapidly go downhill as one crosses the border into SE QLD where it is a whole lot less interesting. IMO, for reliability, Kempsey to Lismore in NSW. For violent storms and structure I like the Hunter Valley or down here in Sydney (traffic aside) -- it simply does tend to be more hit or miss from year to year, and esp over the last decade in these parts where a drier climate cycle seems to be in effect.
