Wednesday 2 to Saturday 5 FEB 2005
National Daily Weather Summary
Major Event

QLD, NSW, VIC, TAS: Wild weather hits eastern states

See also the BoM's report

Between 2 and 5 February, an exceptional meteorological situation brought widespread storms, large hail, hurricane-force winds, torrential rainfall, flooding, duststorms, unseasonable snow and intense heat and cold to eastern states. About 100 rainfall and low temperature records were broken across 5 states, many for locations with over a century of observations.

Wind and flood damage in TAS was put at about $5m, possibly the state's most expensive weather-related damage bill. In VIC, Melbourne City chronicled its heaviest one-day rainfall in 150 years while rainfall records fell across much of central and NE VIC. Across eastern AUS, records for both heat and cold fell in droves -- Balranald NSW shaved nearly 5° off its previous record for a cold February day in nearly a century of observations.

10 to 15cm of snow carpeted the Snowy Mountains as temperatures fell to -5 and wind gusted to 154km/h. Thunderstorms dumped hail up to 6cm diameter across eastern NSW, and severe dust storms raked northern NSW and southern QLD.

Why it happened

A polar outbreak more typical of winter pushed into SE AUS displacing a very dry airmass nearly 30° hotter. The cold airmass -- one of the coldest of the past century to strike the continent during a February -- arrived at the same time as a tongue of very humid, unstable air fed southwards down the NSW coast.

The images at right show the mechanics of this extraordinary event. Click on them for animations or enlargements that show how the event unfolded.

shows the situation mid-afternoon on Wednesday 2 FEB. VIC and southern NSW are buried beneath the cloudmass of a developing low as a cold front sweeps east, whipping up murky brown duststorms several hundred kilometres across in southern QLD and northern NSW, and a line of violent hailstorms in central eastern NSW.

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This MODIS true colour image was taken at 3pm Wednesday 2 FEB.

 

The surface situation is shown in . A heat trough arcing from northern WA through central QLD into inland NSW is a regular summer phenomenon. This was the situation in the first chart in the animation at 10am EST on Tuesday 1 FEB, with a broad 1002hPa low in the trough in southern QLD. Six hours later, pressures over the NSW Riverina had fallen 8hPa as the trough low relocated southwards ahead of the colder airmass just about to arrive on the SA coast.

Overnight, the trough and low continued to move east about 200km ahead of the surface cold front. During the late morning of Wednesday 2 FEB, a low level circulation to the west of Canberra became evident on satellite images and shows as a kink in the cold front on the 10am chart. By the 4pm chart (where the animation pauses), a separate low had been analysed just NW of Canberra while the original low crossed the coast near Newcastle. The Canberra low tracked south across East Gippsland during the evening, its central pressure dropping to 988hPa as it crossed the coast.

By the early morning hours of Thursday 3 FEB the low was approaching Melbourne where it hovered for a day and a half before slowly moving away to the southeast. The low was at its most intense during the early morning hours of Thursday, reaching a central pressure of 987hPa near Wilsons Promontory at 5am EDT. This coincided with the heaviest of the rain in and around Melbourne.

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Surface charts for each 6 hours from 11am 1 FEB to 11am 5 FEB BoM

 

Chart shows the situation at 850hPa or about 1.4km above sea level where temperature, humidity and wind are free from surface influences. Three elements stand out in the static chart at right, drawn for 11pm EDT on Tuesday 1 FEB when the surface cold front lay from the West Coast of TAS to Port Augusta in SA. The first is the huge temperature contrast across the front -- it is 26° over Hillston in SW NSW but only 2° over Adelaide 600km to the WSW. The mean 850hPa temperature over Adelaide in early February is 12°.

The second feature is the depth and uniformity of the cold airmass streaming up from the SSW -- between the SA coast and 55°S, a distance of nearly 3,000km, the airmass varies only between +2 and -4° indicating the strength of penetration of the polar surge.

The third is the stream of high relative humidity ducting down the NSW coast. Humidities are between 75 and 90% in temperatures generally around 20°, representing large amounts of water vapour in the atmosphere at low levels. The high humidity in the cold airmass is misleading, as air at these temperatures carries low amounts of water vapour even when fully saturated.

The animation shows that by the evening of Wednesday 2 FEB most of SE AUS was covered by 850hPa temperatures of around 2 to 4°, a situation that continued until Friday morning after which temperatures slowly rose as the system moved away to the SE. The exception was the tongue of warm very humid air wrapping around the developing low. On the 11pm EDT (12z) chart for Wednesday 2 FEB, this can be seen extending temperatures of around 14° into eastern Bass Strait, punching warmth, moisture and energy into the middle of the cold, unstable airmass -- right over Melbourne. On Thursday 3 FEB this train of warm, humid air moved south over TAS, but left a large legacy of moisture over VIC in its wake.

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850hPa (~1.4km) temperatures, humidity and wind flow. COLA

 

Chart gives considerably more information on the levels and movements of moisture and instability. The lines show precipitable water available -- i.e. the total depth, in millimetres, of liquid water that would result if all water vapor contained in a vertical column of air could be wrung out, leaving the air completely dry. It is a better indicator of the moisture available for potential rainfall than relative humidity which, as the chart above shows, is dependent on temperature. The yellow/brown shading indicates instability using the Convective Available Potential Energy (CAPE) formula.

The static chart at right shows the situation at 11am EDT Wednesday 2 Feb, when moderate to heavy rain had already commenced through central VIC and thunderstorms were occurring in the vicinity of the two lows in NSW, around the Southern Tablelands and in the Hunter. High moisture levels of 40 to 50mm extend down the NSW coast and to the east of TAS, while instability levels are moderate to high across the eastern half of NSW. The cold air pushing into western VIC is much drier -- 10 to 15mm -- but shows mild levels of instability common in post-frontal cold airmasses.

The animation shows that by 12z (11pm EDT) Wednesday 2 FEB, the moisture train had begun to wrap around the intensifying low in Gippsland, bringing levels as high as 50mm into eastern Bass Strait. Between this and the next chart, the moisture train moved over Melbourne giving some of the heaviest rain of the event around dawn. By 00z (11am EDT) Thursday 3 FEB, the moisture had wrapped farther around the low in winds that were onshore to eastern TAS and the western VIC coast. While moisture levels continued to diminish during Thursday and Friday, the train completed a full circle around the low, feeding a rain mechanism that produced heavy rain to the north of the low where winds moved upslope over the VIC Alps.

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850hPa (~1.4km) temperatures, humidity and wind flow. COLA

 

Chart shows the situation at 500hPa, and is representative of conditions in the middle atmosphere. The lines show the height of the 500hPa pressure surface and can be compared with the isobars on a standard surface chart. The static chart at right shows a deep upper cut-off low over SE NSW at the same time as the surface low was moving into Gippsland, to the south of the upper low. Broadscale steering over VIC was cyclonic (clockwise) around this upper low, forcing the surface low to move west into Bass Strait, then continue northwest into the Melbourne area.

The animation shows the development of this cut-off low during Tuesday and Wednesday. By 00z (11am EDT) Thursday, the upper low itself has backslid to the Melbourne area and aligned vertically above the surface low. The entire system, now perfectly stacked and strongly independent, became stationary as external steering forces ceased. It was not until late on Friday 4 FEB that the system began a slow southeastward movement in response to its own weakening and to the arrival of the next upstream trough in the westerlies.

Chart shows that CAPE (instability) was not significant after 12z Wednesday, indicating that the main rain-producing mechanisms were not instability but uplift. The animation for chart shows an enormous area of deep blue surrounding the upper low for much of the period. This represents strong vorticity, or the amount of spin around the low, which produced strong broadscale uplift through the atmosphere. This was enough to produce widespread heavy rain. Very heavy rain occurred where there was additional local uplift caused by the roughness of the surface around coastlines or rising ground in mountain areas.

 

[Click image for animation - 514k]
500hPa (~5.7km) pressure surface heights and vorticity. COLA

Chart shows up and down motion in the lower atmosphere at 700hPa (about 3km). The dotted blue lines represent differing strengths of upmotion. The static chart at right for 12z (11pm EDT) Wednesday 2 FEB shows a bullseye of very high uplift already in place over Melbourne, with a band of equal or greater uplift across Bass Strait. This band aligns with the moisture train in . By 00z Thursday 3 FEB, uplift has moderated, but it seems likely that the enhanced rainfall over Melbourne around dawn was assisted by a continuation or increase in low level uplift.

By 00z Thursday 3 FEB, an arc of moderate uplift covers TAS and western VIC, and bullseyes over NE VIC, all coinciding with areas of heavy rain.

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Vertical velocity at 700hPa (~3.1km). COLA

 

The final chart underlines the strength of the vertical structure of the system and gives clues to its origin. This chart shows windstreams at 200hPa or about 12km in an area where jetstreams roam.

The first frame in the animation shows a major kink in the jetstream had developed by 00z (11am EDT) Tuesday 1 FEB. Windspeeds in the core of the jet along the length of the kink are over 70m/s (250km/h). More importantly, the axis of the jet is nearly due southerly from around 60°S, sweeping cold air swiftly northwards from near the Antarctic coastline. A feature of most severe polar outbreaks in Australia is the development a southerly jet with a long fetch. While everything in the atmosphere is interrelated in a way that makes chickens and eggs seem simple, the kink generated in the jetstream by dynamics on a hemispheric scale could be said to have created this event.

Over succeeding frames, the circulation at 12km can be seen cutting off and aligning above the surface low, producing a broad spinning column of air reaching up to the tropopause.

 

 

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Jet stream distortion at 200hPa (~12km). COLA

What happened

Rainfall for the 24 hours to 9am Thursday 4 FEB (above) and Friday 5 FEB (below). BoM

Tasmania

While events around Melbourne took the media limelight, damage from this event appears to have been greatest in TAS. The Insurance Council of Australia has estimated a total damage bill of about $5m from over 1,500 claims for wind and flood damage. This is believed to have been Tasmania's highest-ever weather-related damage bill.

Wind

With the state squeezed between a 987hPa Bass Strait low and a 1016hPa ridge just southwest of the island, severe and damaging winds began on the NE coastline late on Wednesday 2 FEB and continued throughout Thursday, extending to the NW coast as the low moved near Melbourne. The highest wind gusts reported were Eddystone Point 131km/h, Mount Read 122, Devonport 117, Mt Wellington 106, Flinders Island Aiport 100, Sheffield and St Helens 98, Launceston City and Fingal 96, Launceston Airport 94, and Cressy and Cape Bruny 91.

The N and NE coasts from Devonport to St Helens, including Flinders Island, were worst hit. Many homes were damaged, often by fallen trees, in Port Sorell, while damage was also reported from Devonport and through the Tamar Valley to Bridport, around Scottsdale, Winnaleah (25km ENE of Scottscale) and Binalong Bay (10km NNE of St Helens). Fruit growers in the Tamar Valley suffered extensive damage with up to 50% losses while poppy and grain farmers were also affected. On the Tamar itself, about 25 boats broke moorings with 14 destroyed. A resultant diesel slick at Beauty Point damaged Tamar River aquaculture industries. Across the north, power was lost to about 30,000 premises, some for up to 5 days. Some electricity poles in the northwest were so badly damaged they had to be replaced. Conditions were not so bad in the south, though two boats broke moorings at Sandy Bay, south of Hobart.

Conditions in Bass Strait defy imagination. Storm force winds exceeding an average of 100km/h with gusts to over 140km/h began late Wednesday evening and continued until just before dawn on Thursday. As the low approached, Hogan Island, 50km ESE of Wilsons Promontory, reported several gusts over 140km/h with a peak gust of 150km/h soon after 1am with a sustained 10-minute average windspeed exceeding 110km/h at times. Wilsons Prom Lighthouse reported a 148km/h gust about the same time. The Bass Strait ferry Spirit of Tasmania I, which set out from Melbourne bound for Devonport about 9pm Wednesday hit straight into the storm. She was badly damaged in estimated 20m seas and had to return to Melbourne, a turning operation that no captain would envy. The counterpart sailing of Spirit of Tasmania II from Devonport was delayed, and Spirit of Tasmania III, used on the Devonport-Sydney service, broke its moorings in the Mersey estuary in Devonport and was slightly damaged.

Rainfall and flooding

Heavy rain began in the northeast late on Wednesday 2 FEB and moved down the coast arriving in Hobart early on Thursday afternoon. The maps show overall distribution of 24-hour falls, but many of the totals fell in just a few hours leading to flash flooding, particularly on the East Coast, around Hobart and in the southeast. Minor flood levels were reached in many tributaries of the South Esk River, including the St Pauls River. At Kingston, 10km S of Hobart, the diminutive Browns River broke its banks causing local flooding. Some minor landslides were caused by the heavy rain in the south.

Rainfall for the 24 hours to 9am Wednesday 2 FEB (top), Thursday 3 FEB (above), Friday 4 FEB (below) and Saturday 5 FEB (bottom). BoM

Victoria

Record-breaking 24-hour rainfalls occurred across VIC to 9am Thursday 3 FEB with the heaviest in and around Melbourne. The continuing infeed of moisture wrapping around the low resulted in continued heavy falls through Friday and Saturday in the northeast, while the cold airmass and heavy cloud cover resulted in record-setting low daytime temperatures across the state on Wednesday and Thursday. Gale force winds occurred in the southern half of the state on Thursday, with storm force gusts in coastal and exposed areas. Flooding resulted in central and northeastern streams, and flash flooding was widespread. Extensive damage was reported, with sustained gales and torrential rain combining to weaken and uproot trees and cause structural damage to buildings. Emergency services dealt with over 7,000 calls for help during the period.

Wind

The strongest winds occurred between about 9pm Wednesday 2 FEB and 9am Thursday 3 FEB. The strongest gusts were recorded at coastal and mountain locations: Wilsons Promontory 148km/h, Airey's Inlet 113 and Lookout Hill and Falls Creek 111. On Port Philip Bay, Fawkner Beacon gusted to 104 and South Channel Island to 102. However damaging gusts also penetrated some distance inland, including Melbourne Airport 102, Laverton RAAF 96, Warrnambool Airport 94 and Port Fairy 93.

Rainfall

The volume of rain that fell in parts of VIC not renowned for heavy falls was phenomenal. The Director of Meteorology, Dr Geoff Love, described the event as "extremely unusual because of the wide area covered by the heavy rain. Records are often created in isolated spots, often as a result of slow-moving thunderstorms, but it is much rarer for extreme rainfall to occur across such an area." He compared the event with those of December 1934 and February 1973 as the heaviest rainfall events in the last century across central Victoria. On this occasion, the averaged rainfall across the Central District for the 24 hours to 9am on Thursday 3 FEB was 106.0mm, the highest since district average records began in 1901. The Central Rainfall District covers all Melbourne and extends W to Geelong, NW to Castlemaine, N to Seymour, NE to Eildon, E to include the Dandenongs and SE to Phillip Island.

Gauges around Melbourne with records stretching back over a century had their highest-ever one-day registrations. In the 24 hours to 9am Thursday 3 FEB:

  • Melbourne City registered 120.2mm (previous record 108.0 in 149 years of observations)
  • Durdidwarrah (40km NNW of Geelong) 128.4 (118.4, 131 years)
  • Kinglake West (45km NE of Melbourne CBD) 166.8 (135.4, 122 years)
  • Toorourrong Reservoir (40km NNE of Melbourne CBD) 129.6 (112.2, 113 years)
  • Prahran (5km SE of the CBD) 102.0 (96.8, 111 years)
  • and in the 24 hours to 9am Friday 4 FEB, Avenal (xxxxxxx) 129.4 (110.5, 102 years).

A further 14 locations in Victoria with over 100 years of observations had their wettest February day on record. Perhaps the most remarkable was Dookie, in flat country 35km NW of Benalla, which has 125 years of observations yet managed to break its previous February record of 67.6 on two consecutive days with 90.0 mm on 3 FEB and 103.4 mm on 4 FEB. Full details of new records are in the Daily Weather Summary records sections for 3 FEB and 4 FEB.

Flooding

Streams from the Mitchell River in East Gippsland west to the Otways and northeast to the King River rose rapidly on 2 and 3 FEB. By late Thursday evening, 26 flood warnings were current, mostly for minor flooding but for moderate flooding in the Latrobe, Barwon and Yarra Rivers and Sunday Creek near Seymour. Fortunately, catchments were dry and many dams had considerable headroom, so main river flooding was relatively light for such a heavy rain event. Known flood peaks near or above minor flood level were:

  • Avon at Stratford 5.71m about midday Thursday with minor flooding
  • Thomson at upstream Cowwarr Weir 4.39m 5.20am Thursday, just below moderate
  • Thomson at Wandocka 6.37m 3am Friday, just below moderate
  • Latrobe at Willow Grove 4.30m 9am Thursday, just below minor
  • Latrobe at Thoms Bridge 4.58m about 9pm Thursday, minor
  • Latrobe at Rosedale 4.18m about 5pm Sunday, just above minor
  • Tanjil at Tanjil Junction 4.15 about 3pm Thursday, well above minor
  • Morwell at Boolarra 101.0m AHD about 6am Thursday, just above minor
  • Yarra at Banksia Street is known to have reached exceeded 8.51m at 5pm Thursday, just above moderate
  • Lerderderg at Sardine Creek 2.31m about 11am Thursday, just above minor
  • Werribee at Ballan 2.10 about 10.30pm Thursday, just above moderate
  • Werribee downstream Lake Melton about 3.0 at 11pm Thursday, minor
  • Leigh at Mt Mercer 2.55m about 6.30pm Thursday, just below moderate
  • Leigh at Shelford Bridge 4.97 about midnight Thursday evening, minor
  • Moorabool at Batesford Bridge 4.0m about noon Friday, on moderate flood level
  • Upper Barwon at Ricketts Marsh 4.8m Friday night, on moderate
  • Barwon at Geelong 2.6m around 10am Saturday, just above minor
  • Buffalo at Lake Buffalo outflow 3.14m around 7pm Friday, just above minor
  • King at Docker Road 4.01m about 4am Saturday, just above moderate
  • Ovens at Wangaratta, above 12m overnight Saturday/Sunday, just above minor
  • Broken at Benalla 2.7m about 2am Saturday, just above minor
  • Sunday Creek at Tallarook, slightly above the major flood level of 4.0m on Thursday
  • Goulburn at Shepparton 8.4m about 6am Monday, 1.1m below minor.

Low temperatures

A total of 43 locations in northern Victoria, eastern South Australia and southern NSW had their coldest February day on record on either 2 or 3 February, with some records being extended by 3 degrees or more. Of particular note were:

  • Mt Hotham's maximum of -0.2 on 3 FEB was the first sub-zero maximum ever recorded in Australia in February
  • Longerenong (40 years of observations) set a new record of 16.6 on 2 FEB and equalled it on 3 FEB
  • Echuca (48 years) shaved 5.0° off its previous record with a maximum of 11.8 on 2 FEB, and
  • Kerang (41 years) recorded 11.7 on 2 FEB, 5.3 below its previous record.

The table below (courtesy BoM) shows locations in VIC that set new low maximum temperature records for VIC.

Table 3. Locations with lowest daily maximum temperature for February

Location Date Temperature
°C
Previous
record
°C
Date Number of
years of data
Ouyen 3rd 15.1 16.8 28/02/1987 48
Walpeup 3rd 16.1 17.2 28/02/1987 40
Horsham 3rd 15.5 17.2 8/02/1996 48
Longerenong 2nd/3rd 16.6 17.1 28/02/1987 40
Echuca 2nd 11.8 16.8 28/02/1996 48
Kerang 2nd 11.7 17 28/02/1987 41
Kyabram 2nd 12.5 15.9 1/02/1990 40
Tatura 2nd 13.1 15.6 1/02/1990 40
Benalla 3rd 12.5 16.4 9/02/1996 48
Corryong 3rd 13.1 15.4 22/02/1993 33
Rutherglen 3rd 12 16 3/02/2002 40
Strathbogie 3rd 10.5 13 1/02/1990 31
Omeo 3rd 9.8 11.1 4/02/2002 48
Scoresby 2nd 14 15.5 16/02/1998 37
Melbourne Airport 2nd 13.5 14.9 1/02/1990 34
Lake Eildon 3rd 11.9 14 9/02/1996 34
Maryborough 2nd 11.3 14.2 9/02/1996 40
Mangalore 2nd 12.8 14.3 1/02/1990 46
Castlemaine 2nd 10.5 14 28/02/1993 38
Ballarat 2nd 10 11.1 9/02/1996 48
Ararat 2nd 11.9 13.2 1/02/1990 35

And in South Australia and NSW:

 

Table 3. Locations with lowest daily maximum temperature for February

Location State Date Temperature
(degrees C)
Previous
record
(degrees C)
Date Number of
years of data
Mount Barker SA 3rd 15.5 15.8 20/02/1987 48
Meningie SA 4th 17.7 18 21/02/1993 38
Murray Bridge SA 3rd 17.4 18.3 14/02/1972 38
Keith SA 3rd 16.2 17.2 15/02/1965 43
Lameroo SA 3rd 16.5 17.8 1/02/1960 48
Balranald NSW 3rd 12.5 17.3 28/02/1996 38
Ivanhoe NSW 3rd 19.5 19.7 21/02/1977 42
Yass NSW 3rd 14.5 15 20/02/1966 39
Thredbo Village NSW 3rd 5.4 6.5 22/02/1993 33
Cabramurra NSW 3rd 3.8 4 22/02/1993 44
Hume Reservoir NSW 3rd 12 15.6 9/02/1996 40
Tumbarumba NSW 3rd 8.9 11.4 9/02/1996 38
Wagga Wagga NSW 3rd 13.4 16.4 25/02/1909 132
Burrinjuck Dam NSW 3rd 13.6 13.9 20/02/1966 39
Wyalong NSW 3rd 15.5 16 21/02/1993 46
Corowa NSW 3rd 12 16 1/02/1990 35
Tocumwal NSW 2nd 13.8 16.6 1/02/1990 34
Narrandera NSW 3rd 13 17.8 4/02/2002 33
Deniliquin NSW 2nd 11.7 15.1 18/02/1951 144
Hay NSW 2nd 13 17.7 22/02/1996 48

A summary of press reports of incidents during these four days will be added when time permits.