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Wednesday, April 14: Sydney’s Superstorm By Michael Bath* At SILICON CHIP, we have something of a fascination about lightning. Perhaps it’s the immense amount of energy involved. Perhaps it’s because of the damage we’ve seen it cause. Perhaps it’s because it IS fascinating! It’s It's when the lightning is a little close to home, though, that fascination can turn to fear! This is the story of the “big one” which didn’t get away – officially Australia’s most costly natural disaster. O ur fascination pales into insignificance when compared to some “storm chasers”: amateurs (mostly) who study storms – and all their components – with amazing dedication. Often they’re more up-todate than the official Weather Bureau! Michael Bath is one such storm chaser. We’ve seen his work before in SILICON CHIP. Michael not only chases storms, he photographs them. He writes about them. He follows their progress as closely as he can. He has even set up a website dedicated to them (see separate panel). Which brings us to early in the day of April 14, 1999. Michael takes up the story: In the hours before the storm which hit Sydney, the email, internet connections and phones of the storm chasers were buzzing. The weather bureau issued no warnings – it was as if they missed the event completely despite being contacted with very reliable information (as you will read later). The day started out with a casual 10  Silicon Chip comment that “maybe a storm is possible today”. Some altocumulus cloud about, a moisture haze and a forecast of a thundery day for Canberra were the reason for this outlook. By late morning small cumulus clouds had developed in a line from the far southwest towards the coast south of Sydney. But by early afternoon some were starting to spread out as altocumulus – not usually a good sign for thunderstorm development. One or two of the larger clouds actually glaciated (meaning they took on a classic, towering anvil shape) but with very low tops, probably no more than 4-5,000 metres but these were persisting somewhat (something I had observed a few times in the past, but I did not make the connection at the time). Altocumulus began to dominate and it became mostly cloudy during the middle of the afternoon. The only sign that something may occur later was more crisp cumulus congestus (large cumulus cloud masses which grow higher than they are wide – a classic sign of a cloud mass developing into a storm) way to the south, just visible under the altocumulus in Sydney. Around 4pm it became apparent that the congestus to the far south was certainly looking promising and worth keeping an eye on. I suspected that some storms might get going very close to the coast south of Sydney and then remain out to sea, but perhaps a lightning show would result. By 5pm I could see that a thunderstorm was gathering strength about 80km SSE. Having a good feel for locations/distance of storms, I made a mental note that it appeared to be over land in the southern Wollongong area. It would most likely just move offshore and that would be it. However, the tower had a very strong vertical appearance (on the NW flank that I could see), indicating a very strong updraft and the potential for severe weather. I wanted to check the radar to give me an indication of any other develop- matically on its NW flank as the storm edged over the coast, indicating that it could clip the coast again to the north – over Sydney’s southern suburbs. “The bureau was warned. . .” The classic anvil-shaped thunderhead towering sometimes thousands of metres above the surrounding cloud. This is caused by the updraft of moisture-laden air currents in the cell. When the moisture condenses in the cold higher levels, the air current cannot support it and it falls as rain. If it freezes, it can fall as hail, although most of it melts before it reaches the ground. ment and to determine the direction of movement of the storm but didn’t get to see it until after 6.30pm. Lightning could now be seen about 50km SE at this stage. From a website I subscribe to, I downloaded the latest Sydney radar images covering the period 5.30pm to 6.30pm local time. Then I received my email. A message on the aussie-weather mailing list reported that a severe storm had just been through the Shellharbour area (about 100km south of Sydney) and that golf ball sized hail was reported to the local radio station. The storm looked very severe with lowerings, or parts of the clouds jutting out significantly lower than the rest or the base of clouds, almost to the ground. The system was back-building dra- The email author said that he had in fact phoned the Bureau of Meteorology at 6pm to report the storm, only to be greeted with scepticism. If we could see what was happening, why couldn’t the Bureau? Obviously he was dismissed as an unreliable spotter as no severe thunderstorm advice or warning was issued (although one was belatedly issued at 10.20pm, long after the storm had passed). By 7pm it was obvious on both radar and visually (my home is about 40km from the coast) that the storm was moving directly NNE and heading straight into the southern Sydney suburbs. In fact by 7pm there was already maximum reflectivity on the radar and the storm was over the Royal National Park on Sydney’s southern outskirts, heading towards Botany Bay and Sydney Airport. Lightning was frequent to the south-east but it seemed that a dead cell or other cloud was to the west of the storm, blocking the view of any lightning bolts. I could however see the glowing outline of the storm tops and reflections around the rest of the sky. Visually it continued like this until Left: thermal image of the storm taken by the NOAA12 satellite at 7.13UCT (9.13pm Sydney time); courtesy of CSIRO. Above is the radar image taken at around the same time with the storm sited directly over Sydney’s eastern suburbs, which copped the brunt of the damage; courtesy Bureau of Meterology. JULY 1999  11 Everyone has a story... by James Crouch, Rushcutters Bay. It was about 7:35pm. I had about two minutes warning – I could hear a distant roar but didn’t know what it was at first. It just got louder and louder. Things started breaking as soon as the first isolated hail stones began falling: neighbour’s windows, roof tiles, that sort of thing. The roar was quite loud but still distant. For a moment it sounded like “things” were falling out of the sky and I actually feared for a few seconds that it was debris, not ice!! The tiles on my roof were taking a pounding, ceiling plaster was flaking off all over (I guess a combination of hail and tile impacts). There was nothing I could do and I didn’t have a view, so I went down to the street and sat under shelter with a few neighbours and watched as 70mm hailstones slammed into the footpath. I couldn’t see much in the way of cloud but there was lightning every 2-3 seconds. Bayswater Rd, empty of traffic, was covered in a 50mm layer of ice (ice was still piled up in corners 3 hours later). The heaviest hail lasted about 10-15 minutes and then it rained (showered, whatever) until 2am-ish. That was the killer. I drilled a few holes in my ceiling where it was sagging the worst (and until I ran out of pots and pans) and then checked my neighbours. I wasn’t the worst; the girl across the landing had a 2-3 litre per minute flow from the light in her kitchen for a while, and sundry other leaks of various flow rates. I climbed up into the ceiling: there were at least 300 tiles shattered or cracked; you could see the sky all over the place. Once they’d isolated her power and we’d drilled holes in other peoples ceilings, I went and checked my car. It was a Daihatsu Feroza. The bonnet was trashed – 20-odd 4-5cm dents and one of the rear side windows was smashed – with a bit of resultant water damage. Not so bad. . . I haven’t got onto the insurance company yet so I have no idea when it’ll have a chance to get fixed up. Meantime I guess that I’m up for driving on storm chases! I had a pleasant night’s sleep on cushions in the hallway – that was the only place that didn’t have leaks!! just as in Sydney. It can also make the storm rotate and is the phenomenen which also breeds tornados. In most thunderstorms, the updrafts of air reach a point where the water and ice they contain cannot be supported and they collapse, dumping their rain and sometimes ice (as hail) in the process. A second storm Towards 9pm, fresh southeast winds spread in with a layer of strato-cumulus, blocking the storm as it edged out over the northern beaches. At about the same time the first reports of giant hail began to filter in and the discussions on the ’net got quite excited. Also at this time, another storm with hail passed through the eastern suburbs on a similar track to the supercell. Later (between 10pm and 11pm) a storm with some intense cloud-toground strokes spread through the western suburbs dumping some heavy rain but no hail. Brief blackouts occurred including at my place at 11pm. It wasn’t until the next day that the analysis of the day’s observations and the radar clearly showed the significance of the event. The radar patterns were classic supercell from about 6.30pm onwards with a clearly defined V-notch most of the time. The V-notch is a particular shape of the radar image on the screen, well known to meteorologists as an indication of a very severe storm. Almost a tornado 8pm though was now much closer and bigger. Radar showed the most intense part of the storm was right over the eastern suburbs and city and would have been smashing these areas with hail officially measured to 9cm diameter, with larger stones probable. Just after 8pm the storm became much more spectacular from my vantage point to its west – continuous cloud to cloud lightning, cloud to air, and cloud to ground, though I could only see the top half of these. It coincided with a rapid propagation and development to the NW of the main thunderstorm, making the whole structure visible with each lightning flash. Is it a supercell? With a boiling rear flank, a rock 12  Silicon Chip solid backshearing anvil punching well through the tropopause and the continuous lightning, I soon came to realise this was no ordinary storm. In fact, it looked to me like the western flank of a supercell thunderstorm. In fact, after spending some time taking lightning photographs I made the remark that I thought it was a supercell and wondered what damage had occured or was currently occurring in the most densely populated parts of Sydney. A supercell thunderstorm is fairly rare – perhaps one a year or so in the Greater Sydney area – and occurs when the updrafts and downdrafts of air currents within the storm occur at the same time due to windshear. This makes the storm self-sustaining. A supercell is much more likely to do a lot of damage over a wide area – It was disturbing to see a most prominent hook echo on the radar screen when the storm was right over the eastern suburbs, though no damaging winds were experienced there. A hook echo on the screen can indicate precipitation actually wrapping around a meso-cyclone. Imagine if a large tornado had touched down as well! The storm tracked to the NNE and was well defined for almost four hours. Contrary to some early reports, there was no cell splitting or another storm suddenly developing closer to Sydney – the one storm cell just propagated on its NW flank continuously. The early afternoon observation of persisting low topped glaciated cells has preceded supercell development on other occasions. As at 11th May, the total insured damages bill is in excess of $A1.4 billion, now making it the most costly natural disaster in Australian history, surpassing the Newcastle earthquake (1989) and Tropical Cyclone Tracy in Darwin (1974). Although the time of year and the area affected by the storm is unusual for a supercell, many hailstorms with similar-sized hail (but officially recorded hail sizes slightly smaller than this event) have occurred in Sydney, even in recent years. Most notable were the supercell hailstorm of Sunday 18th March 1990 affecting the western suburbs and the supercell of Monday 21st January 1991 affecting the northern suburbs. However, insured loses for these two events are far lower than for the April 1999 event. Just after 8pm the storm became much more spectacular from my vantage point to its west – continuous cloud to cloud, cloud to air, and cloud to ground lightning, though I could only see the top half of the latter. * Michael Bath is the editor of the severe weather newsletter, “Storm News” and has a huge library of storm and lightning photo-graphy. He also conducts a website dedicated to the subject of severe weather at www. australiansevereweather.simplenet.com On this site there are links to many other sites on similar subjects. Radar Image courtesy Bureau of Meterology. Satellite image courtesy CSIRO. Tracking the Storm by Tracking the Lightning Regular S ILICON C HIP readers would be aware of the LPATS Lightning Positioning and Tracking System (see the article in the November 1996 issue). As you might expect, Kattron's Ken Ticehurst had been monitoring the storm earlier in the day, just as had Michael Bath. “We could see the storm's path bearing down on Sydney and were amazed that the weather bureau didn’t issue any warnings,” said Ken. “In the overall scheme of things, though, this thunderstorm didn’t look all that big because most of the lightning was CC strokes”. LPATS works by detecting the electromagnetic radiation of a cloudto-ground (CG) lightning stroke between 2 and 450kHz. Some cloud-to-cloud (CC) strokes are also detected but as their radiation is mainly in the VHF range, the detection range is much less. In most thunderstorms, CCs are usually 90% of the lightning activity. In this storm, with all the hail, it may well have been higher. Certainly from the SILICON CHIP offices (close to the coast in northern Sydney) the impression was overwhelmingly CC, even with the numerous CG strokes witnessed (actually CW or cloud-towater because most of the activity was by this time off shore). The lightning display, by the way, was rated by SILICON CHIP staff as easily the most spectacular they had ever seen). But in terms of CG activity this storm was not all that ferocious – with around 600 strokes per hour at its peak (11.30pm). At 8.30pm, about the peak of damage in the Eastern Suburbs, it was recording 120 strokes per hour. We have seen thousands of CG strokes per hour (over a greater area) in other storms. (The November 1996 article shows a graph of lightning strokes in Central NSW during November 1995 peaking at more than 3800 mainly C-G strokes per hour!) The map above shows one of the lightning stroke “maps” plotted by Kattron during the storm. The colour bars on the images represent % of strokes in 10 minute intervals from the time shown (top left of each image), starting with gray. Each screen in the full series represents 1 hour. SC JULY 1999  13