Strong front brings temperature extremes, violent weather and welcome rain
Fri 9 Nov 2018

Heatwaves, snow, storms with high wind gusts and large hail, a massive dust storm, abnormally hot and cold November temperatures and some drought-relieving rain were all in the weather mix in the week to Friday 9 November.

Heat built in a sultry trough that moved across the country during the week, bringing a wave of heatwave-strength night and daytime temperatures as it advanced. Maximum temperatures reached over 42° in northern WA, large areas of the NT and QLD, and northern NSW. Moisture from NW Australia streamed into the country producing some cracker thunderstorms in the unstable air in the trough.

From Monday 5^th, a strong cold front began pushing across the south of the continent, undercutting and lifting the moisture and producing some worthwhile rain across large parts of SA, NSW and VIC as well as the south of the NT and QLD. However, because much of the rain came from thunderstorms, results were mixed in pastoral and cropping areas. The Australian Bureau of Agricultural and Resource Economics and Sciences (ABARES) said "In cropping regions, rainfall totals were highly variable. Falls of between 10 and 50 millimetres were recorded in southern New South Wales and South Australia. Falls of between 10 and 25 millimetres were recorded in parts of southern Victoria and Western Australia. For remaining cropping regions, little or no rainfall was recorded."

Among significant events during the week:

• Heatwave conditions began building across SE Australia late in October with Ceduna, Whyalla and Mt Lofty all reporting top temperatures 15° or more above average on Wednesday 31^st. Record-breaking high daytime temperatures appeared from the beginning of November. On Thursday 1^st Darwin reported its equal highest November maximum in 77 years of observations with 37.3° while on Friday 2nd Green Cape, which juts well out into the Tasman Sea near the far southeastern tip of the continent, utterly demolished its previous November high temperature record of 28.0° with a reading of 34.7°. The highest temperatures during the build-up of heat were in NE SA, SW QLD and NW NSW, and were not record-breakers but still very high for November. They included Urandangie QLD 44.0° and White Cliffs NSW 43.3 on the 2^nd, Birdsville QLD 44.3 on the 4^th, Windorah QLD 44.0 on the 5^th, and St George QLD 43.1 and Moree 43.0 on the 6^th. Sydney Airport with a maximum of 38.9 and Wollongong Airport at 38.2 were close to 15° above the November average on the 2^nd.
• High overnight temperatures were a feature over a much broader area and more records fell than daytime maxima. The Newcastle NSW area had their warmest November night in around 70 years on Saturday 3^rd with minima of 23.1° recorded at both Nobbys Signal Station and Williamtown RAAF Base which have 61 and 69 year histories. Sydney's Observatory Hill reached 22.5, not quite matching its most sleepless November night since 1857 of 24.8. On Tuesday 6th, it was Brisbane's turn to sweat through the night with the Amberley RAAF Base minimum of 23.8° its highest in 77 years; Brisbane City's low of 23.5 felt worse with high humidity brought in on the previous day's sea breeze..
• Storms were active across a large area of WA on Sunday 4^th, and a very active area of thunderstorms worked its way across central and eastern SA during the late afternoon and evening of Monday 5^th. At Tarcoola on the Trans-Australian Railway, 360km NW of Port Augusta, one storm hit just after 18.00 with a 117km/h wind gust, the highest on record for the settlement. At the same time, 12.8mm fell in less than 15 minutes. Two and a half hours later, a second storm dumped 32.0mm on Tarcoola in one hour, 13.6mm falling in just 10 minutes. When rain eased off, there was 48.2mm in the gauge, the heaviest November one-day total in 115 years of observations.
• As a trough and wind change ahead of the cold front pushed storms into northwestern NSW late afternoon on Tuesday 6^th, it raised a large dust storm. An SMH story gathered these images and a dramatic video showing what it was like to meet the dust storm while driving - in a word, black. Much of the area had recorded less than 50mm rain since the start of the year and, as the video shows, the 5 to 15mm that fell in the region from the storms immediately following the dust storm turned everything to mud.
  
• The Melbourne Cup only just missed the wrath of thunderstorms as they swept across Melbourne on the first Tuesday in November, the 6^th. Between 35 and 61mm were unloaded on all but the outer southern and outer NE suburbs in a few hours as the trough and thunderstorms crossed the city. While it stayed dry for the main event, it was the second wettest Cup Day on record giving Melbourne more rain in two hours than it had had in the previous two months. City streets flooded, fourteen people had to be rescued from flooded vehicles and the SES received 400 calls for help. A minor flood warning was issued for the Lower Yarra. A helpful graph tweeted the day before by VIC BoM shows you definitely need a versatile wardrobe to go to Flemington.
• A supercell thunderstorm with giant hail, up to 9cm in diameter, moved ENE from Rollands Plains to Kundabung, 25km NW of Port Macquarie NSW, on the afternoon of Wednesday 7^th. In another thunderstorm, a man driving a 4WD 10km NW of Taree narrowly missed impalement when lightning hit a tree by the road causing it to explode and spear a branch through his windscreen. ABC carried a more detailed description and photos of this unusual event as well as video of the giant hail.
• By Wednesday 7^th, the cold front moving into NSW set up a sharp contrast between hot temperatures in the mid 30s to low 40s across northern NSW and southern QLD and much colder air in the low to mid teens farther south. The density contrast between the two airmasses caused a strong jet stream to develop near their boundary reaching over 340km/h at times.
• Cold day and night temperatures in the wake of the cold front reached record levels in places, especially in WA on Wednesday 7th. Salmon Gums (half way between Norseman and Esperance) had its coldest November morning in 79 years of observations with -1.2°, the old record having stood since 1958. Ongerup had a record November low in 51 years of obs, and six other stations in the South West with shorter histories set new lows, all breaking records set on 2 November 2005. Perth's temperature got down to 8.0°, its coldest for November in eight years. The cold nights were not as severe in eastern states, but West Wyalong recorded an unusually low November maximum of 12.3° on the 7^th, knocking 3.6° off the record, as rain and thick cloud behind the front kept the temperature down.
• In TAS, it was as if winter had returned with snow reported on the Central Highlands on Wednesday 7^th and the temperature dropping to -2.9 at Liawenee the next morning. On Thursday, Scottsdale in the northeast recorded -0.5, its coldest November morning in 35 years while Launceston City's 0.4 was its coldest in 15 years. Farther north, wintry hail showers fell over southern VIC and Melbourne on Wednesday night and snow returned briefly to the Alps in both VIC and NSW. The Thursday Alpine minima were decidedly wintry with -5.9 at Thredbo Top Station, -5.4 at Mt Hotham and -5.0 at Falls Creek. A number of places across VIC and NSW had their coldest November morning in 12 years.
  

[BoM, Andrew Miskelly, ABC, SMH, Weatherzone]