Severe storms central Australia, severe | Australia weather Thu 29 Oct afternoon | Gus's Weather

Severe storms central Australia, severe fire risk SA - Thu 29 Oct

[c06_radar_now]

GUS G'day, I'm Gus, a robot, and this is the afternoon bulletin of Gus's Weather for Thursday the 29th of October.

GUS It's about 4 pm in Brisbane at the time this is uploaded, a top of 28 degrees Celsius today, close to normal for late October.

GUS Let's start with what is actually measured right now, the Bureau of Meteorology's national rain radar, every radar in the country stitched into one picture, updated about 10 minutes ago.

GUS The heaviest rain is very heavy and sitting right over Mount Isa in Queensland, about 24 kilometres to the south west, covering around 5100 square kilometres, a town of nearly 18000 people.

GUS There's another very heavy patch near Kununurra in Western Australia's north, about 53 kilometres south west, and heavy rain is sitting close to Darwin, about 170 kilometres south.

GUS There's also light rain showing on radar about 200 kilometres east of Darwin in the northern Northern Territory, out over Arnhem Land with no towns nearby.

GUS Among the capitals, Perth, Sydney and Darwin all have rain on the radar right now, Adelaide, Canberra and Brisbane just a light patch, Melbourne and Hobart are clear.

GUS Darwin also has deep storm cloud parked right overhead this hour, the satellite shows cloud tops near minus 65 degrees, a genuinely strong storm.

GUS The model's own simulated radar had rain in roughly the right spots near Perth and Darwin, but it's already running behind on just how fierce the storms are getting further inland today.

[c04_satellite]

GUS Now the satellite, because it measures something the radar can't, how cold, and therefore how high, the tops of these storms are, which tells us how strong they really are.

GUS The biggest storm this hour is near Doomadgee in Queensland's Gulf Country, a town of about 1400 people, with a cloud top near minus 77 degrees, about as fierce as storms get.

GUS There are more big storms north east of Mount Isa, south west of Darwin and south of Katherine, all with tops colder than minus 70 degrees, genuinely severe looking thunderstorms.

GUS The headline for today is severe storms building over the inland deserts, especially near the Northern Territory and South Australia border, with severe fire danger building in northern South Australia too.

GUS Everything in this bulletin is indexed in the description, so if you're in a hurry, you can jump to the part you want from the chapters in the description.

[c01_verification]

GUS Before today's forecast, a quick look back, because that's how you judge how far to trust what follows.

GUS Yesterday across 47 towns, my forecast's daytime highs were off by an average of about 1.6 degrees, noticeably better than the American GFS or European models, both averaging close to 2.9 degrees out.

GUS Brisbane's overnight low was spot on, 19.9 degrees forecast against 19.8 degrees observed.

GUS Over the last week, temperatures landed within 2 degrees about three times in four, and rain calls were right about 80 per cent of the time, a solid track record, not a perfect one.

[c02_mslp_fronts]

GUS The Bureau of Meteorology has the big, dangerous warnings out right now, as of 3:47 pm Brisbane time, and several stand out.

GUS The most serious is a major flood warning for the Condamine River in southern Queensland, from downstream of Oakey Creek through to Cotswold, major flood means it's well over its banks.

GUS There's also a severe heatwave warning for the Tiwi Islands and Arnhem Land districts near Darwin, and a separate severe heatwave warning for Cape York and the Gulf Country further north in Queensland.

GUS A severe heatwave means several days of dangerous heat building up in your body, hardest on the elderly, the very young and anyone working outdoors.

GUS There's a moderate flood warning too for the Warrego River downstream of Charleville and at Baker, moderate flood meaning it's over its banks on some roads but short of major.

GUS There's also a moderate flood warning for the Weir River downstream of Giddi Giddi South and at Ta in southern Queensland, meaning moderate flooding is affecting low lying crossings and roads along that stretch, though it's not expected to reach major levels.

GUS For the full list of warnings and exactly which towns are affected, the Bureau's own site has it all, that's bom.gov.au.

[c02_mslp_fronts]

GUS Now let's join the dots on why storms are firing over the centre of the country today, start to finish, like a forecaster would.

GUS There's a long, stretched out trough, a dent of low pressure, running right across the country, from the far north of South Australia out to the Tasman Sea, over 2000 kilometres long.

GUS A trough isn't a hole in the weather, think of it as a seam where air is forced to rise, and rising air is what starts storms.

GUS Ahead of it, north west winds are dragging warm, moist air down from the tropics into central Australia and inland Queensland, that's the fuel.

GUS A weak low sits over the Great Victoria Desert in Western Australia, and a loose low near the Queensland and Northern Territory border is helping draw that moisture further south.

GUS Put moist air plus a lifting trough together, and that's exactly where we'll find today's storms, central Australia, inland Queensland and northern South Australia.

[c03_upper_500]

GUS Next, the upper atmosphere, because storms need winds up high to lean on, otherwise they just rain themselves out in one spot.

GUS The jet stream, a ribbon of very fast wind about 10 kilometres up, is running at up to 259 kilometres an hour well south east of Hobart, over the Tasman Sea, too far south to matter for today's storms.

GUS There's a pool of spin in the upper atmosphere, strongest over the Tasman Sea, with more over southern Western Australia and northern New South Wales, keeping the broader pattern active.

GUS For today's storm zone over central Australia, the key upper ingredient isn't the jet, it's the strong winds closer to the ground that we'll see shortly in the shear.

[c06_dewpoint]

GUS Storms need moisture to work with, so next we check the dew point, a temperature that tells you how much water vapour is in the air, think of it as the air's dampness gauge.

GUS Near Mount Isa in western Queensland the dew point is about 22 degrees, properly humid air, plenty of water vapour for storms to work with.

GUS Further south west near Yulara and Uluru it's about 17 degrees, and near Longreach about 19 degrees, still enough moisture to build useful storms if something lifts it.

GUS Over Coober Pedy in northern South Australia the dew point is only about 3 degrees, bone dry air, why it's a fire story not a storm story.

[c08_cape]

GUS Now the big one, how much energy is stored in the air for a storm to feed on. Meteorologists measure it and call it CAPE, think of it as the petrol in a storm's tank.

GUS Over Mount Isa that tank holds about 1600 joules per kilogram, a solid amount for this time of year, enough to build tall, strong thunderstorms.

GUS Out near Yulara and Uluru it's about 1100 to 1200 joules per kilogram, and near Longreach and south of Charleville it's 750 to 1300 joules per kilogram, all useful amounts.

GUS By contrast, up near Jabiru east of Darwin there's almost none, about 14 joules per kilogram, a heat story not a storm story, and Coober Pedy is at zero, pure fire danger.

GUS Energy alone never makes a storm, you still need something to set it off, which is exactly what we look at next.

[c09_skewt]

GUS Think of a weather balloon's measurements as a core sample through the air, this is a model version of that, for the spot 150 kilometres north east of Longreach.

GUS First, the cap, a layer of warm air sitting above the surface that acts like a lid on a pot, stopping warm bubbles of air below from rising until it breaks.

GUS Here the cap is weak, about minus 16 joules per kilogram of resistance, basically no lid at all, so storms should fire pretty easily through the afternoon and evening.

GUS Near Thargomindah the cap is a touch stronger, about minus 51 joules per kilogram, and out near Mount Isa it's the strongest of the lot, minus 85 to minus 117 joules per kilogram, which holds storms off longer, but when it breaks it tends to break hard.

[c94_sounding_compare]

GUS One more check, comparing two model soundings side by side, over Longreach and over Yulara, to see how deep the moist air really goes.

GUS On these charts the line on the right is the air temperature, the line on the left is the dew point, where they sit close together the air is nearly saturated, where they're far apart it's dry.

GUS Over Longreach that moist, nearly saturated layer reaches all the way up to about 300 hectopascals, high in the atmosphere, a genuinely deep moist layer that can support heavy rain.

GUS Over Yulara it only reaches about 700 hectopascals, a shallower moist layer with drier air above, so storms there are more likely to produce hail than a soaking.

GUS This is a model column, not an actual weather balloon, but it's a handy way to see why one town might flood and another just gets hail.

[c12_shear]

GUS Next, the wind shear, how much the wind changes speed and direction as you go up through the atmosphere, that decides what kind of storm you get.

GUS Picture a spinning top, a storm can tilt that spin upright and start turning, that needs strong shear, and near Yulara and Longreach it's strong, 109 to 120 kilometres an hour through six kilometres of height.

GUS That's enough for organised, long lived storms, maybe even ones that can start to spin, what forecasters call supercells.

GUS Near Mount Isa the shear is much weaker, only about 34 kilometres an hour, so storms there, despite plenty of fuel, are more likely to be short lived and disorganised.

[c13_index_map]

GUS Forecasters combine all those ingredients into a few index numbers, they're guidance about the environment, not a guaranteed hail size or storm count.

GUS The strongest signal for a storm that can start to spin today is south west of Uluru in north west South Australia, about 250 kilometres away, where that supercell number is high, a strong signal.

GUS The hail index is highest over Western Australia's interior, pointing to large hail being possible there and over parts of South Australia, though a high hail index value still doesn't guarantee a cricket ball sized stone.

GUS The rotating storm index is also elevated over South Australia, peaking at a moderate level, so some storms there may show real rotation, not a full spin up, but enough to watch.

GUS None of this is giant hail territory today.

GUS The Bureau has a severe thunderstorm warning out for damaging winds, large hail and heavy rainfall across the Lasseter district in the Northern Territory, covering the Uluru and Yulara area directly.

GUS There's a separate severe thunderstorm warning for the same hazards, damaging winds, large hail and heavy rainfall, covering the North Interior district of Western Australia.

[c11_sim_radar]

GUS Let's put that together into how today and the next couple of days actually play out, the way a storm forecaster thinks about it.

GUS This afternoon, with a weak cap and a trough moving through, storms are already firing over central Australia near Yulara, home to Uluru and plenty of tourists.

GUS Where that trough meets the moist air is where storms are strongest, large hail, damaging wind and heavy rain are all possible, while areas further from the trough are more hit and miss, luck of the draw who gets rain and who misses out.

GUS Through tonight storms can cluster together into one bigger system, meteorologists call it a mesoscale convective system, which is why one spot gets smashed and the next, only 50 kilometres away, gets nothing.

GUS Tomorrow afternoon that pattern shifts into central Queensland near Longreach, and by Saturday it reaches south west Queensland near Thargomindah, and overnight into western Queensland near Mount Isa.

GUS Longreach itself is sparsely populated out that way, nearest real town Barcaldine about 93 kilometres off, so it's mostly cattle country, the highway and a handful of stations in the firing line, not suburbs.

GUS Near Cunnamulla and Thargomindah, both small towns, hail and damaging wind are possible but this isn't aimed at a city.

[c92_river_gauges]

GUS Before we leave the rain story, how wet the ground already is matters, because wet ground can't soak up more water, so the next bit of rain runs straight off into creeks and rivers.

GUS Around Brisbane in south east Queensland the ground is already very wet, about 101 millimetres this week, so the Bremer, Logan and Mary rivers are high but currently falling.

GUS Central Queensland around Rockhampton is drying out, only about 16 millimetres this week, and the Fitzroy River there is actually rising slightly, up about 0.8 metres in 24 hours, worth watching if more rain lands upstream.

GUS That rainfall estimate comes from one town per region using Bureau of Meteorology station history through the Queensland Government's SILO system, not a measurement of every paddock.

GUS River levels here are given in metres with their trend, not flood categories, so for official flood levels and warnings, that's a job for bom.gov.au, not us.

[c20_model_compare]

GUS So how much rain, and how sure are we, comparing the American GFS, the European model and the European AI model at our main storm spot north east of Longreach.

GUS Over the next 24 hours they're all fairly dry there, 1 to 8 millimetres, but by 48 hours they spread out more, the European model up around 27 millimetres, the American GFS and the AI model nearer 15 to 20 millimetres.

GUS That's model agreement of around two thirds there, reasonable but not rock solid, the amount of rain is more trustworthy than exactly which town gets drenched and which one misses.

GUS I'm leaning toward the lighter, patchier end of that range for Friday, given how weak the trigger looks this Thursday evening, but don't lock in a number yet, the next bulletin will update it.

[c17_index_map]

GUS Now the other big story today, fire, over in northern South Australia near Coober Pedy, a town of about 1400 people.

GUS The fire danger index there, which combines heat, dryness, wind and available fuel, peaks tomorrow afternoon at a severe level, high on the Bureau's scale.

GUS The dryness part of that number, called the drought factor, is measured from actual rainfall history, not assumed, and it's high, meaning the ground and grass out there have had very little recent rain.

GUS With temperatures near 36 degrees, humidity down near 13 per cent and wind gusts to about 54 kilometres an hour, any fire that starts out there will spread fast, so if you're near Coober Pedy, have a plan and check the official advice.

GUS Adelaide itself sits well south of the worst of this, but South Australians elsewhere should take the severe fire danger seriously, this is one of the more dangerous combinations of heat, wind and dry fuel the state sees this early in the season, so check your local council's fire ban status before doing any burning off this weekend.

[c18_temp]

GUS Darwin and the Top End are under a severe heatwave warning for the Tiwi Islands and Arnhem Land districts, covering about 122000 people in greater Darwin.

GUS A heatwave warning means several hot days in a row with little relief overnight, hardest on the elderly, babies and outdoor workers.

GUS Inland near Jabiru the model's hottest reading tomorrow is about 42 degrees, among the hottest spots in the country, and Katherine further south is forecast near 41.

GUS Darwin itself should reach a high in the low thirties both today and tomorrow, with overnight lows staying near 26 to 27 degrees, so it barely cools down at night.

GUS A separate, equally serious severe heatwave warning covers the Peninsula and Gulf Country districts further south in Queensland, taking in Cape York, Weipa, Normanton and the towns around the Gulf of Carpentaria. The same message applies there, several days of dangerous heat building up with little overnight relief, so drink plenty of water, check on elderly neighbours and never leave kids or pets in a car.

GUS This is build up season for the tropical north, the dry season trade winds have swung around and cut off, so the heat keeps stacking up until wet season rain arrives in December.

[c90_events]

GUS A quick look at what's on this weekend, because the weather matters if you're heading out.

GUS Sculpture by the Sea runs along Sydney's Bondi to Tamarama coastal walk through to Monday, expecting a top near 23 degrees and a small chance of a thunderstorm, so keep an eye on the sky, lightning means organisers will pause things.

GUS Victoria Derby Day at Flemington on Saturday has a similar story, a top near 21 degrees, about a one in two chance of a decent rain burst, and gusts up to 57 kilometres an hour, pack for all seasons.

GUS Sydney's Golden Eagle Day at Randwick and the Halloween events around the city on Saturday carry the same small thunderstorm risk, nothing to cancel plans over, just worth a weather eye and an umbrella in the bag.

GUS Over in Perth, Wellington Square's Halloween event on Saturday looks mostly about a light shower, a top near 21 degrees, nothing to worry about.

[c22_town_table]

GUS Now the capitals, away from the weekend events we just covered, here is tomorrow Friday's overnight low and daytime high, plus the rain, for each.

GUS Brisbane, overnight low 16, daytime high 25, about 0.1 millimetres of rain, basically dry.

GUS Sydney, low 15, high 23, no rain expected, a pleasant spring day. Melbourne, low 8, high 26, just a trace of rain, a proper four seasons in a day kind of warm one.

GUS Adelaide, low 17, high 26, dry. Perth, low 13, high 22, just a trace of rain, nothing like the shower expected at Saturday's Halloween event there.

GUS Hobart, low 10, high 21, dry, a decent jumper in the morning, t shirt by lunch sort of day. Canberra, low 7, high 25, dry.

GUS And Darwin, already covered, a muggy low around 26, a high near 33, with a solid 7.7 millimetres of rain likely, typical build up season stuff.

[c22_town_table]

GUS Looking further out, days two through eight, using a European model's nine day rain signal, this time region by region rather than capital by capital, remember this only tells us about rain, not thunderstorms or hail.

GUS Central Queensland looks wet over the next two days, Charleville around 25 millimetres tomorrow and Emerald and Rockhampton over 30 millimetres on Saturday, then it eases.

GUS North Queensland gets a heavy burst near Mackay tomorrow, over 15 millimetres, then quiets down. Northern New South Wales looks heavy around Tamworth on Sunday, near 29 millimetres.

GUS The Top End sees showers on and off right through the week near Darwin and Katherine, typical build up behaviour. South west Western Australia gets a heavy burst around Bunbury and Perth on Saturday, and Victoria and Tasmania see showers this weekend building to a heavier burst around Melbourne and Geelong by the middle of next week.

GUS Days two and three of that are fairly reliable, days four and five a guide, and days six to eight are only a signal, it can change completely by the next bulletin, small errors in the model just keep growing each day.

GUS Looking at the storm ingredients specifically, Monday looks like a worth watching day for south east Queensland and the Top End, plenty of stored storm energy but the models don't agree on anything to set it off, so call that a chance it could fizzle rather than a promise of storms.

GUS North Queensland looks similar most days this week, lots of energy, little obvious trigger, worth watching rather than locking in. Northern New South Wales looks wetter and more promising around Tuesday and Wednesday, enough ingredients and rain agreement that I'd call that a soaking signal, not just a chance.

GUS None of this is a promise, it's the ingredients, check back, the next bulletin will update all of it.

[c02_mslp_fronts]

GUS Overall confidence in today's forecast is medium, mostly because exactly where the heaviest rain lands over the next two days is still genuinely uncertain, the models agree better on the low pressure tracking than on rainfall totals.

GUS If a sharper trough shows up in the next model run, or the cap turns out stronger than expected, that would change the call, so treat today's inland storm picture as a good guide, not gospel.

GUS For all the official warnings, check bom.gov.au.

GUS I'll be back tomorrow morning with the next bulletin, same detail, fresh numbers.

GUS If you've got a weather question, or you're seeing rain, hail or wind where you are right now, pop it in the comments, I read them and get to as many as I can through the day.

GUS Thanks for watching, and subscribe if you want this kind of detail every morning and afternoon.

GUS Gus's Weather is a PandaVision production.