BAMOS Vol 30 No. 4 2017 - Page 39

Charts of the Past BAMOS Dec 2017 with Blair Trewin 39 17 March 1950 The years 1949–50 brought a strong La Niña to the Pacific Ocean. The summer of 1949–50 was somewhat wetter than normal over most of eastern Australia but there was a marked change in conditions in March, which was exceptionally wet. The most significant rain event of the month began as a monsoon low over northwest Queensland on 14 March. Over the following days it moved south, and was centred near Broken Hill by the 16th, and in the far southwest of New South Wales on the 17th. It then gradually became absorbed into a trough over inland New South Wales which eventually weakened in situ. The low initially brought very heavy rain to the far west of Queensland, with 246 mm at Burketown over two days from 14–15 March, and 138.7 mm at Urandangi on the 15th. The resultant rise in the Georgina River forced the evacuation of Urandangi, and widespread major flooding ensued in the region, with the Diamantina at Birdsville eventually having its second-highest flood on record(after 1974). The next stage of the event, as very moist air moved southward, affected the eastern outback of South Australia, and adjacent border areas of New South Wales. Numerous stations had falls exceeding 100 mm, with the highest daily totals of 188.0 mm at Wooltana (near Arkaroola) on the 16th, and 181.1 mm at Frome Downs on the 17th, both of which were all-time daily records. Extensive flooding also resulted in this region, interrupting coal supplies to South Australian power stations due to damage to the Leigh Creek railway. Over the following days, the major areas affected moved further south and east. There was extremely heavy rain in parts of north-central and north-east Victoria on the 18th and 19th. East Noorilim, near Murchison, had 227.3 mm on the 19th and 269 mm over the two days, whilst Murchison itself had 275 mm Rainfall totals 18–24 March 1950. over this period. Mount Buffalo had 174 mm on the 18th and several sites in the Strathbogies exceeded 150 mm. By then the rain had also extended into southern inland New South Wales, with lower peak daily falls but large accumulations over several days. The heaviest falls were in and around the Brindabella Ranges between Canberra and Tumut. Brindabella Station had 492 mm in the week 18–24 March, whilst Canberra itself had 248 mm in six days (although the wettest day had a relatively modest 64.8 mm), more than Canberra Airport has reported in any other calendar month. The extreme rainfall in this region caused major flooding in the Murrumbidgee catchment, particularly from the Tumut River which was not yet regulated (Blowering Dam had not yet been built). This eventually caused large-scale inundation at Wagga Wagga, which had its second-highest flood peak of the 20th century. The town levee system had not yet been built and large parts of the central city were flooded (something which had been a regular occurrence in the early 20th century but less common after Burrinjuck Dam was completed). More than 1,000 houses were evacuated, and one person died. Other river systems were less affected, although there was significant local flooding around Murchison on the Goulburn River, as well as in the Snowy. March 1950 went on to be the wettest on record over much of the Southern and Central Tablelands of New South Wales, as well as parts of northern Victoria and eastern South Australia, and much of far western Queensland. This began a very wet period, with 1950 going on to be the wettest year on record for New South Wales, and the second-wettest (after 2010) for Queensland. Synoptic chart for 1500 AEST, 17 March 1950