SYNOPTIC ANALYSIS OF THE
FIRST NATIONAL AUSTRALIAN STORM CHASE
1st to 7th October 1998
Clyve Herbert
OVERVIEW
I started out on my journey north to meet up with the Sydney Storm Chasers and weather enthusiasts for a planned expedition to northern New South Wales and South Queensland on the 2nd October 1998. I could not imagine that I would more or less be able to keep tabs on a weather system as it moved through Victoria on the 1st October, bringing to an end a five day warm spell, progressing slowly into New South Wales on the 2nd, moving up the east coast of New South Wales during the 3rd, 4th & 5th and then finally dissipating over southeast Queensland late on the 5th of October.
The previous week (late September) was disappointing for the 1st stage for the Sydney chase team, with almost the whole week being dominated by a persistent anticyclone. Fortunately, during the second week, as this weakening frontal / trough system edged northward along the NSW coast, the second attempt at a successful chase was fulfilled. Although on Saturday the 3rd October the front and trough passed through the Sydney area with only cirrus bands and a few week cumulus developments, and at that stage things looked a little grim. Conditions looked a lot more promising on Sunday morning as the clearing edge of the trough was marked by a line of altocumulus castellatus. A hasty phonecall to Jimmy Deguara was made, and together with Michael Thompson, Paul Yole and myself, we headed north.
As the trough edged north on Sunday 4th, the diurnal heating destabilised the airmass along and north of the through line. As the chase team approached the Liverpool Range, north of Muswellbrook, deep convection was well underway. The first glaciated tower developed around 2pm and within 30 minutes this single cell had merged with other cumulus congestus to form a line of multicells with overshooting tops and glaciating anvils.
Over the next several hours as we moved along the New England Highway, the area of activity along the Liverpool Range persisted and progressively drifted eastward towards the central coast. It was still visible well to the south as we arrived at Glen Innes for our overnight stay. At this location we were well ahead of the surface trough and planned a possible chase the next day around the far north of NSW.
Early on the 5th, a view to the south of Glen Innes showed a line of altocumulus castellatus edging northward and this line had similar characteristics to the trough which had passed over Sydney on the previous morning. The chase team decided to set a location just north of Glen Innes for most of the morning, however not much happened except for scattered congesting cumulus and patchy high cirrus. Cloud growth to the north showed more potential, so we decided to head towards the Queensland border and set up a viewing location at Tenterfield.
By 2pm, congesting cumulus were well underway to the west of Tenterfield and a persistent cumulonimbus had developed about 20kms to the north. This took our attention and we headed across the Qld border to intersect this system, which turned out to be a good move. As the storm weakened, the outflow downdraft was already driving up a large new development along its southeastern flank. This growth area was soon to become the dominant storm. The chase team headed along a narrow road appropriately named Storm King Dam.
We arrived just in time to see this sytem become severe, with a strong rear flank downdraft and updraft interface, and a developing flanking line. This storm produced 2cm hail and torrential rain, and we eventually tracked around its eastern side to reveal a large back shearing anvil and overshooting top. This turned out to be the highlight of the chase. At this time. around 5pm, Michael Bath obtained a high resolution satellite image showing this storm in progress:
Image courtesy of CSIRO Marine
Research Remote Sensing Project
5th October 1998 - 0523Z (4.23pm EDST)
After this excitement we headed toward Stanthorpe for an overnight stay and a great evening of discussion and video viewing. Conditions changed rapidly overnight of the 5th of October and in the early hours of the 6th, as a deep low pressure system developed west of Tasmania. The upper flow at 300hpa increased considerably across South Queensland and was generating extensive middle and high level cloud.
The low west of Tasmania pushed an active cold front into NSW and southwest QLD. This gave the chase team a rare view of an active cold front crossing southeast QLD. The team positioned themselves on a lookout above Stanthorpe and we watched the cold frontal system roll across, preceded by strong north westerlies, a period of moderate rain and a sudden shift of wind to the south west, followed by much colder conditions.
By early on the 7th this cool southern airmass had covered most of southern QLD and it was interesting to see cumulus lines developing in this southern airstream. Unfortunately this spelled the end of activity over this region and we decided to head south. As we moved across the northern tablelands we encountered daytime temperatures as low as 8C, even in bright sunshine. This cold air mass had dropped the snow line down to 400 metres over southern Victoria the previous day. We arrived at Tamworth for lunch and we again had considerable discussion about events of the previous days. With reluctant good-byes I headed west to join up with the Newell Highway and then south to Victoria.
This storm chasing journey gave me the opportunity to witness the progression of a weather system which produced a remarkable variety of meteorological conditions. Being able to view the dynamic and diurnal changes that occurred over a distance surpassing 2000kms was one of the best meteorological lessons I have ever experienced.
FOOTNOTE
Many thanks to Jimmy Deguara for organising this first national storm chase and bringing together weather enthusiasts from all around Australia (Hailstone Jimmy) and thanks also to the remaining storm team: Michael Thompson (The Storm Surfer), Michael Bath and Paul Yole (The Apprentice).
Updated 22nd May 1999 - J ONeill