storm reports
March 18, 1998... Destruction in the Brisbane Valley
The Weather Bureau was not too confident when issuing the forecast. A trough expected to pass through the area the night before had stagnated, so the risk of late storm activity remained. I was definitely expecting something, especially after the brief severe storm with golf ball hail over the Border ranges the day before. From 2pm I began to see t'storm anvils over the western and southwestern horizon through the heat haze of a typical Brisbane 'stinking' hot day. The maximum temperature earlier was 33C; the winds were light to mod NNE and the 3pm humidity was way up at 74%.
The first STW for the SE Coast district was issued at 4:10pm, with scattered thunderstorms tracking and developing over the inland areas. The Weather Bureau (and I) were particularly interested in a probable severe cluster of storms to the SW of Brisbane, but to my dismay by 4:40pm I noticed it had begun to weaken. It was its NE side that had weakened, but then it propagated on its NNW side, slightly strengthening the storm. As it became darker outside frequent lightning became apparent as it moved north, which was west of my position. Probably 98% of the lightning was sheet and seemingly low to the ground, but the power of the strikes made me realise these were really CG bolts behind heavy rain and/or hail.
Meanwhile, to my south on the Border Ranges, pulses of TCU and Cb developed continuously with the odd spectacular flash of CG and CC lightning, but these never really moved off the ranges. On radar, they appeared to be briefly severe with hail. The atmosphere was obviously still very unstable even after the passing of the inland storm. Naturally, I hoped we could get something later that night.
The inland storm continued to track north. After moving through the Laidley, Esk and Buaraba Creek areas as a non-severe storm, it rapidly intensified causing severe damage in a small Brisbane Valley town called Harlin, west of Kilcoy. Several houses and a petrol station were unroofed, sending galvanised iron flying through the main street. At the local pub, patrons had to take cover when golf ball hail smashed through the southern windows, and nearby water tanks were peppered with hailstones until it resembled a large strainer. Just out of town, the storm was at it's most severe when 5 large power pylons were blown over into masses of crumpled iron. It is understood that these structures were built to withstand wind gusts of at least 180km/h, so one could say that winds were near 200km/h during the storm. With such extreme wind gusts, it was surprising that no tornado tracks were found, but it was determined that straight-line downdraughts were responsible. The final Severe Thunderstorm Warning was issued near 7pm with the severe storm beginning to weaken, but other weak and isolated activity remained.
Later that night, weak lightning became apparent to the south and by midnight thunder was occasionally heard. Over the next five hours or so, continuous bands of low-top thunderstorms moved through Brisbane and surrounding coastal areas with torrential rain. Ahead of the surface trough and helped along by some cold air in the upper levels, the storms unusually moved SSE-NNW and were concentrated in Northern Brisbane suburbs. In this area falls were in the 65-160mm range: Manly 150+, Wynnum 140, Lytton 68, and Toombul 67mm. Over the Border Ranges, where the storms initially developed there were unofficial reports of over 200mm, while a local heavy fall occurred just south of Brisbane, where 112mm fell at Ormiston. Because the rain fell a month after the last decent falls over the area, only minor flash flooding was reported in the Northern Brisbane area.
