North Coast Storms: Monday 20th May 1996
by Leith Martin
At 3:05 p.m. the storm had formed a new cell at a bearing 240 degrees from here, and appeared to be drifting to the east, south of Lismore. VHF radio static estimated range at approximately 60 to 70 km. At 4:05 p.m. the storm changed direction to north east, then suddenly to the north, with indications in cloud of strong wind. The Barometer rose quickly from 1010 to 1012 hPa.
At 4:10 p.m., strong winds hit Goonellabah, gusting to 40/50 knots from the SSE with rain.
One storm cell passed to the west, between Lismore and Dunoon, and another to the east, between Lismore and Alstonville. The storm abated at 4:35 p.m., clearing from the west, with wind veering is the south east. Total rain registered was 13.8 mm. Note that the wind gusts remained high from beginning to end.
Three of those watching are Radio Amateurs, situated at Goonellabah, Dunoon and Ballina. We kept constant contact on VHF (146.800Mhz), through the Repeater situated at Parrots Nest, between Lismore and Casino. As the storm progressed, communication was lost between individuals and the repeater, and also between each other on direct path. This occurred at different times for all of us.
It is assumed that this loss of propagation was caused by severe wind turbulence in or adjacent to the storm cells as they passed between us and the repeater, and between each other. Interruption to the path was preceded in nearly every case by severe flutter of the signal, similar to that heard during "Aircraft Enhancement".
We unanimously conclude that it was caused by violent wind shear, not an uncommon occurrence with VHF and especially UHF TV. I understand that this is common phenomena with tornadoes.
Rainfall in the area included 15mm at Lismore, 12mm Casino and 25mm Nimbin.
Updated: 6th April, 2004
|[Australian Severe Weather index] [Copyright Notice] [Email Contacts] [Search This Site]|