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Hail and Hailstorms

 

 

October 26, 2003 - Hail - just how big can it get?

Hailstorms range in intensity from those that frequently develop in winter producing hailstones no larger than a green pea, to violent supercell thunderstorms that produce giant hail stones larger than tennis balls. Such storms are potentially very destructive and are certainly a threat to human life. The storm that occurred near the NSW town of Grafton on October 26, 2003, was an example of the latter.

Following a review of the weather models the previous night, it was apparent that any storms that were to develop on the 26th would surely be violent, with tornadoes and giant hail possible.

We made the long trek north from Sydney via the Pacific Hwy - some 9 hours drive, passing through a severe hailstorm mid-way at 11:30 in the morning. As we arrived at Grafton, a thunderstorm exploded to our north. The 'splitting' storm would cross the highway in front of us. Vehicles were parked by the roadside and for good reason - giant hailstones littered the road with passing cars exhibiting seriously broken windshields.

Hail on Pacific Hwy near Tyndale, Northern Rivers District, NSW

 

As we ventured further north into the storm's core, these massive hailstones pounded our vehicle. We let the storm edge further east. By this stage hail was infrequent, however was composed of enormous hailstones, all being ejected out the back of the storm's 16 km high updraft.

When finally safe to do so, we walked around the near edge of a field, adjacent to where we had parked, to measure the size of the stones. Note many of the stones were jagged rather than truly spherical.

Above: Giant hailstones, each measuring 7-8cm in diameter

The size of the hail astounded us. We have encountered similar size hail while storm chasing in the US Great Plains and also in Australia. Having said that, this was the largest we had ever actually measured.

Above: a size perspective of a giant hailstone

Following some 'ice-fossicking', we then attempted to intercept the culprit storm which had moved east and cleared the highway. As we did so, the rear flank of the supercell was visible. By the time we found a road option east, the storm had cleared the coast, effectively ending our chase.

Above: Supercell moves off the coast of northern NSW

 

As we headed back to Tyndale and waited, with more storms developing to our south, we re-visited the area where the largest hail appeared to fall. I literally had to dig out a huge stone that was within a softball sized crater in a residents front lawn. This hailstone had undergone considerable melt, given that 90 minutes had passed since the storm's passage over the area. We believe this to be the largest hailstone actually ever measured in Australia -- 9.6 cm diameter, although larger hailstones would surely have fallen in this storm and, certainly, other east coast supercells in days gone by.

Above: One of the largest hailstones ever measured in Australia

 

The hailstone shown above would have been traveling at between 150 and 200 kilometers per hour when it hit the ground. The growth time for a hailstone this size is likely to be between 40 and 60 minutes. It would have grown at heights ranging from about 3 to 12 kilometers at temperatures varying from about 0oC to -35oC. Hailstones larger than 6 inches in diameter fell in the US state of Nebraska in June 2003 - the largest ever measured anywhere in the world.

 

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Hail Size:

Size [cm]	Descriptive term
0.3	Pellet, rice
0.5	Small hail
1.0	Pea, musket ball
1.5	Cherry, grape, nutmeg
2.0	Marble, lark egg, gooseberry, bullet, Australian 5 cent coin
2.2	Australian 10 cent coin
2.7	Australian 20 cent coin
3.0	Australian 50 cent coin
3.5	Table tennis ball
3.7	Walnut
4.0	Pigeon egg
4.2	Golf ball, goose egg
5.5	Chicken egg, pullet egg, duck egg
6.0	Billiard ball
6.3	Tennis ball
7.0	Cricket ball
8.0	Fist, orange
10.0	Grapefruit

 

 

 

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