Page:Hunt - The climate and weather of Australia - 1913.djvu/169

Rh barometer fell extraordinarily—to 28.40 inches—but the value of the reading is unknown. On the same afternoon at Richmond (Q.), 800 miles away, a "terrific cyclone" damaged most of the buildings, derailed railway trucks, and bent double iron telegraph poles. Two inches of rain fell.

On the preceding afternoon, near Laverton (W.A.), a thunder and hailstorm, giving half-an-inch of rain, was accompanied by a "hurricane."

Though violent, the foregoing are not absolutely identifiable as tornadoes, but the observer's description of a storm next day at Gemville, a place in the dry north-western interior of New South Wales, leaves little room for doubt. The 5th, he said, will long be remembered. One inch of rain fell in half an hour, hail stripped the ground bare, and a "cyclone," the spiral motion of which was a feature, cut a track through the scrub several miles long. The thunder and lightning were very severe. The description of a local storm of extreme severity and destructiveness in North-eastern Victoria is of interest, and shows that tornadoes or very similar phenomena may occur under other than summer conditions of heat, humidity, and barometric pressure. About 3 a.m. on the 16th July, 1904, near Avenel, a "fierce wind" swept from N.W. to S.E. over a strip of country about 2 miles long and 30 yards wide. It completely wrecked a farmhouse which lay in its track, killing two of its inmates, carried large pieces of furniture for over half-a-mile, tore up trees by the roots and transported them for considerable distances, and demolished all of an orchard over which it passed. The storm was immediately preceded by vivid lightning and heavy peals of thunder. The weather charts of the 15th and 16th July show that this occurred in connexion with the final stages of a very intense Antarctic low-pressure system which had been moving slowly eastwards along the south coast-line for five days previously, and suggest that it was coincident with a sudden rise in barometric pressure which ended the "Antarctic" and introduced anticyclonic conditions. The passage of a low-pressure trough usually coincides with a maximum of atmospheric instability, and in this case it seems probable that the exceptional energy developed was in some way connected with the arrival of the colder and denser air of the anticyclonic front—possibly by this causing forced ascent of the warmer and moister air of the low-pressure system. But whichever was cause or whichever effect, we know by experience that a sudden change from cyclonic to anticyclonic conditions, as shown by a large rise in barometers at the end of a lengthy period of Antarctic low pressures, is almost invariably associated with violent atmospheric disturbances and not infrequently thunder and hail storms.