330 



On the morning of the hailstorm, May 12, the storm 

 centre occupied about the same position as on the preceding 

 day, but the energetic "high" on the west, with a maximum 

 reading of 30'3°, had advanced slightly during the 24 hours 

 producing steeper gradients, while the storm area had 

 widened out to the eastward, taking in the whole of the 

 south-eastern quadrant of the continent, including Tasmania, 

 bringing rain over this area from Cape Leeuwin to Brisbane. 

 The lowest reading of the barometer at Adelaide was coin- 

 cident with the storm burst that passed over the city. The 

 thermograph records for the day, courteously placed at my 

 disposal by Mr. E. Bromley, the Divisional Officer of the 

 Weather Bureau, showed that, immediately in front of the 

 storm there was a sudden rise of temperature, amounting to 

 6°, and as sudden a fall, to a like extent, immediately after, 

 and thereby established a contrasted temperature grade, as 

 well as a steep barometric grade, in adjacent regions, condi- 

 tions very favourable for the development of electric and 

 hailstorm effects. The main vortex of the disturbance 

 appears to have developed near Adelaide, causing convection 

 up-draughts and down-draughts of exceptional energy. The 

 unusual size of the hailstones probably arose from successive 

 accretions that followed on the rapid and repeated inter- 

 change of conditions to which the hailstones were subjected 

 in their flight between the lower and upper layers of the 

 cloud. 



At my request Mr. Bromley has kindly supplied the 

 following interesting particulars as to the weather conditions 

 prevailing at the time : — 



"Weather Conditions over South Australia between May 10 



and May 1£, 1917 . 



"The passage across South Australia of an energetic dis- 

 turbance between May 11 and 14, 1917, was marked by very 

 unsettled weather over the southern and coastal portions of 

 the State, and on the 11th and 12th — more particularly the 

 latter date — exceptionally severe hail and thunderstorms were 

 experienced, but chiefly over parts of the metropolitan area 

 and Mount Lofty Ranges. 



"The depression was first noted on the 10th, having 

 pushed up suddenly over the Bight. It was then only of 

 moderate intensity, but on the following morning it had 

 increased considerably in energy and covered the whole of 

 the State, with its centre south of Adelaide. The disturb- 

 ance was connected inland by a trough of low pressure which 

 stretched northwards to the Gulf of Carpentaria. 



"A- large anticyclone covered the whole of Western Aus- 

 tralia on Friday (11th), and although this system spread 



