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SEVERE THUNDERSTORM – 31st March 2009

A squall line associated with a vigorous low pressure system crossing the Maltese Islands early this morning spawned a dry macroburst from high-based thunderstorms. The sounding on the right taken at around 5am shows a sounding typical of a dry macroburst.

A macroburst is an intense downdraft generated from the thunderstorm as the raindrops evaporate and the downdraft reaches the ground not accompanied by rain. The air – cooled by evaporating rain – crashes downward almost like a rock in a pond. The cooler, denser air accelerates downward and then spreads rapidly outward in strong gusty winds near the surface.

Two cars were damaged when a wall collapsed in Fgura in an incident which is thought to have been caused by these strong winds. The south-south easterly wind, which was at its strongest at about 4 am, is also thought to have been the cause of a number of stones falling from an apartment block in St Julians. The stones fell onto the roof of an adjoining house, causing a partial collapse. No one was injured. The strong wind also uprooted trees in several localities, notably at Sta Lucija. Policemen and members of the Civil Protection Department were on hand to give assistance.

Maximum gusts at around 4.15am associated with this macroburst which affected mainly the southern and eastern parts of Malta were: 86.9km/h at Zebbug, 88.6km/h at Naxxar, 92.0km/h at Msida, 93.0km/h at Tarxien, 83.7km/h at Zejtun and 80.6km/h at Iklin. These maximum wind speeds correspond to Force 9 and 10 on the Beaufort scale.

PHOTOS TAKEN BY JAMES DELMAR AND CLINTON CARUANA