On April 14, 1999 the morning weather reports in Sydney Australia said 'a storm is possible today' then a rather unusual phenomenon happened The area in and around Sydney expects around eight days a year to have hailstorms, and normally in the afternoon around two o'clock. Sydney can expect hailstorms anywhere from August to February. On April 14th the hailstorm happened slightly south of the metropolitan area and also along the costal Suburbs at 8pm ( 6 hours later than hailstorms normally happen.) It was reported that there was 1.7 billion dollars in damages, the most damaging event in Australia.In the last 42 years one third of Australia's insured damage has been caused by hailstorms. Annually in the United States hail causes 1.7 billion dollars in damages, this only a small portion of what Australia goes through. They spend around 1 billion dollars in a very rare storm that left their city in shambles after the hail stopped.

The Storm resulted in an estimated 500,000 metric tons (tonne).1 tonne is equal to 1,000 kg or 2,204.62262 lb, so obviously this storm was catastrophic. Over the first five hours of the intense storm, over 2000 emergency calls were taken, approximentally one call every 10 seconds. All these calls were from distressed residents in the Sydney area, reporting that their roofs had been destroyed by the huge hailstones, there was flooding in and around their houses, some of them even had collapsed ceilings and electrical fires. Within a few hours of the storm hitting, the suburbs were declared disaster areas and the Government invoked a State of Emergency, giving full control of the incident to the State Emergency Service (SES). There were 9 emergency services and they were all very quick to respond to all the distressed calls that were coming in. Some of these services were: Police Rescue, Fire Service, Army and the NSlW Fire Brigades. The Fire Brigades were one of the major supporters in helping with the crisis, they sent 700 firefighters to help with the clean up a day, making it the single most largest event in the history of their organisation.

Thunderstorms are the most common natural hazard to occur in Sydney Australia than any other, and because it is the most frequent insurance statistics show that, over the past few years, severe thunderstorms have been the cause of the majority of the damaging events. Normally when an area is prone to a certain natural hazard it is hard for home-owners or even businesses to get that preticular insurance. For example people that live on the sides of mounts or right on a cliff do not qualify for landslide insurance, beacuse they say you know the risks when you move in and the probability it will happen is very high so they will no insure you for fire insurance when you live in the middle of the woods. More than likely people that live in Australia can not get hailstorm insurance. So the guy with big holes in his windsheild below has to pay out of his pocket because his car insurance will not pay for it.

cloudy_day_in_austrailia.jpgFigure 1- a photo taken by weather men rightbefore the storm hit.

The unusual part about this hailstorm were that some of the hailstones were reported to be nine centimeters in diameter, and the biggest hailstone dimensions of that day was reported as nine by eight by eight centimeters. That would be equiviant to a tennis ball. Hail is a form of precipitation that falls from the sky as raindrops of ice. The raindrop can range in size from small pea-sized drops of ice, to hailstones as large as grapefruits (very rare to see). When they are close enough for us to see they can be different shapes, such as: a sphere, cone, or other wierd shapes. Depending on the the environment a hailstone can be hard or soft (dense or nondense) most hailstones that came down on April 14th were very dense and hard like treewood.



Below is FIgure 2- a picture of a hailstone that is about the size of
the some of the ones that were seen in Sydney on the day of the
phenomenon.
HA10x.jpg car.jpg
Above and to the right is FIgure 3- a picture of the hailstones that crashed through car
windsheilds. The size of these hailstones are featured in figure 2.

Hailstones are formed in thunderstorm clouds that are very strong, in particular those with intense updraughts, high liquid content with large water droplets and where most of the clouds temperature is below freezing. Hailstones form dust, various insects or ice crystals with condensation on them.Then when those items are supercooled the condensation on them freezes causing a small ball to form.If hailstones get big enough, they can become quite heavy for the thunderstorm to keep them in the air and they fall out of the thunder cloud and onto the Earth.

Hailstones are most commonly only five millimeters to five centimeters in diameter. They can get to be 15 centimeters wide and weight more than half a kilogram. The most common size of hailstones in severe thunderstorms is about thirteen millimeters(the size of pea or even a golfball), but in the Sydney hailstorm they got to be the size of a grapefruit. As seen in the picture above, Figure 3, hailstones on the larger size can cause very serious damage to cars, crops, skylights in houses or hotels, and even structures with glass roofs. On rare occasions hailstones that are massive can been known to cause concussions or even deaths. In the sydney hailstorm was reported that three civilians were killed by hailstones.

There are three basic conditions needed to trigger a storm of this magnitude: 1. Instability, 2. A trigger, 3. Wind shear. FIrst is instability the air needs to be warm and moist near the Earth’s surface then be trapped under cooler, dryer air in higher altitude in the sky. Then for a storm to be triggered there needs to be a sea breeze or mountain breeze in the air to carry the warm surface air to the cooler higher air.Once that happens a wind shear is created, which is the difference in wind speed and direction. Wind shear happens so that the storm does not collapes on it self, and can go on for hours if needed to. When all this happens heavy rain fall occurs and if he weather is cold enough the small droplets will turn into hail like they did on the cold night in April when one of the biggest hailstorms in history broke out in Sydney.

Hail storms are so destructive, that scientist are researching ways to mitigate them. The most effective method so far is to "scatter either dry ice or silver iodide crystals in clouds that threaten to produce hail"(How Stuff Works). This method increases the number of hail stones formed, but drastically decreases their size. If the stones are small enough they will melt into harmless rain by the time the hit the ground.

Below is a link that will take you to youtube.com and show you a video of the sydney hailstorm that someone took.
Hailstorm Video

Bibliographys
Australian, Govenment. "What causes severe Weather?". Geoscience Australia, . November 20, 2009 <http://www.ga.gov.au/hazards/severeweather/causes.jsp>.

Bath, Michael. "Sydney Hailstorm: Wednesday 1. 4th April 1999". Storm news and chasing. November 29, 2009
<http://australiasevereweather.com/storm_news/1999/docs/9904-01.htm>.

Leigh, Ron, Stephan Yeo, and Ivan Kuhne. "The April 1999 Sydney Hailstorm." 5.2 (1999): 23-25. Web. 4 Nov 2009. http://www.ema.gov.au/www/emaweb/rwpattach.nsf/VAP/(084A3429FD57AC0744737F8EA134BACB)~The_April_1999_Sydney_hailstorm.pdf/$file/The_April_1999_Sydney_hailstorm.pdf.

Leigh, R., I. Kuhnel . "Hailstorm Loss Modelling and Risk Assessment in." Natural Hazards 24.2 (2004): 171-185. Web. 4 Nov 2009. http://www.springerlink.com/content/gj90j6025g6886x1/fulltext.pdf?page=1.

Leigh, R., S. Schuster, R. Blong, and K, McAneney. "Characteristics of the 14 April 1999 Sydney hailstorm based on." Natural Hazards and Earth Science System 5. (2005): 613-620. Web. 4 Nov 2009. http://www.nat-hazards-earth-syst-sci.net/5/613/2005/nhess-5-613-2005.pdf.


"Ten Years Since The Great Sydney Hailstorm!" Storm Chasing Forum - storms tornadoes and tropical cyclones.12 Mar.2010. Web.
<http://www.australiasevereweather.com/forum/general-weather-all-topics-that-are-not-current-severe-weather-should-be-posted-here/ten-years-since-the-great-sydney-hailstorm!/?action=printpage>.

"Hail." How Stuff Works. 10 Mar 2010. Web. <http://science.howstuffworks.com/hail-info.htm>.


"The Sydney Hailstorm - 14 April 1999." Australian Government, Bureau of Meteorology. 12 Mar 2010. Web. <http://www.bom.gov.au/weather/nsw/sevwx/14april1999.shtml>.