Severe storms threaten inland NSW and Qld | Australia weather Fri 30 Oct afternoon | Gus's Weather

Severe storms threaten inland NSW and Qld this weekend

[c06_radar_now]

GUS G'day, I'm Gus, and this is the afternoon bulletin for Friday the thirtieth of October.

GUS The big story is severe storms building over inland New South Wales and southern Queensland through the weekend, with a severe thunderstorm warning already current in central Queensland and major flooding on a western river.

GUS It's about 4 pm in Brisbane at the time this is uploaded.

GUS This is the Bureau of Meteorology's actual radar for the whole country, not a computer model, and the newest picture is only about ten minutes old.

GUS The heaviest rain right now is well inland: a very heavy cell about 90 kilometres north-east of Longreach in Queensland covering around 3,000 square kilometres, with another big one just south-east of Longreach too.

GUS Further west, a very heavy cell sits about 110 kilometres north of Port Lincoln in South Australia, more very heavy cells sit near Fitzroy Crossing and Kununurra in Western Australia's north, and a heavy cell sits about 50 kilometres north-west of Blackall in Queensland.

GUS Of the capitals, Darwin has heavy rain, Adelaide and Canberra have rain, Melbourne, Hobart and Brisbane have lighter rain and storm cloud on satellite, and Perth and Sydney are clear.

GUS Outside the circles on that picture the radar simply can't see, so I won't guess, and the model's simulated radar broadly matches these areas, though it under-does some of the activity out west, so I'm trusting this real radar first today.

[c04_satellite]

GUS Now the satellite, because it measures how cold, and therefore how high, storm tops are, which tells us how strong a storm really is, and it can see where there's no radar at all.

GUS The newest picture is from about 3 pm. The coldest storm tops anywhere in the country are about 80 degrees Celsius below zero, over remote country north-east of Derby in Western Australia.

GUS Picture that: air shooting up through the atmosphere so violently it's colder than minus eighty, higher than most airliners fly, in under an hour.

GUS There are also very cold tops, around 77 degrees below zero, close to Darwin, including one only about 100 kilometres north of the city.

GUS So the pattern: storms build over inland New South Wales and southern Queensland this weekend, heatwave warnings further north, and flooding rivers out west. Everything here is indexed in the description, so jump to the part you want from the chapters there.

[c05_obs_now]

GUS Before any forecast, here's what's actually fallen since nine o'clock this morning, straight off Bureau of Meteorology weather stations, no model involved.

GUS The wettest spot so far is Pirlangimpi in the Northern Territory with 25 millimetres of rain. Charleville in Queensland has had almost 17 millimetres, and Port Lincoln and Cummins in South Australia have both had around 16 millimetres.

GUS It's still raining right now at several of those spots, including Charleville and those South Australian towns.

GUS The strongest wind gust measured anywhere in the country today was 63 kilometres an hour at Kadina in South Australia.

GUS That's all measured, not forecast, credit to the Bureau of Meteorology for that data.

[c07_lightning_now]

GUS Quick check of lightning too, from a volunteer network called Blitzortung, which tracks strikes across the whole country and can show storms firing between radar sweeps.

GUS The busiest cluster today is about 110 kilometres south-west of Blackall in Queensland, with roughly 300 strikes picked up in the last six hours, though it's easing off now.

GUS There's also a smaller, growing lightning cluster over that same stretch of South Australia we mentioned earlier, near Port Lincoln.

GUS That network is a volunteer sample, not an exact count, so treat the numbers loosely. For any official danger, it's always bom.gov.au.

[c06_radar_now]

GUS Before the detail, the Bureau of Meteorology has some serious warnings out, as of 3:37 pm Brisbane time, and these always come first, ahead of my own analysis.

GUS The most serious is a Major Flood Warning for the Condamine River in southern Queensland, downstream of Oakey Creek to Cotswold, with significant flooding already affecting farmland and roads along that stretch.

GUS There's also a Moderate Flood Warning for the Bulloo River downstream to Quilpie and at Quilpie itself, and for the Warrego River near Charleville and Cunnamulla.

GUS There's an Extreme Heatwave Warning for the Tiwi District and a Severe Heatwave Warning for the Arnhem District near Darwin.

GUS There's also a Severe Heatwave Warning for the Peninsula and Gulf Country Districts in far north Queensland, where several days of dangerous heat are expected across the stations, mining camps and small communities out that way.

GUS And there's a current Severe Thunderstorm Warning for damaging winds, large hail and heavy rain across the Central West, Channel Country, Maranoa and Warrego districts of southern Queensland.

GUS Those are the Bureau's warnings, not my forecast, and the full detail for every one of them is on bom.gov.au.

[c02_mslp_fronts]

GUS Now let's build the cause and effect behind the weekend, using the pressure map and the upper winds, because that's how a forecaster actually works it out.

GUS At the surface there's a high over the Tasman Sea east of Coffs Harbour at 1025 hectopascals, a lazy old high doing very little, and weaker low pressure out near the Great Australian Bight.

GUS The more important feature is about five and a half kilometres up, where a long upper trough, a dip in the winds that drags cooler air south and helps lift storms, stretches from the Coral Sea down over inland New South Wales by Saturday.

GUS Through the weekend that trough digs in, and surface winds swing to carry warm, moist air up from the Coral Sea into inland New South Wales and southern Queensland. Where that moist air meets the trough is where storms fire hardest.

GUS So: warm moist air from the north and east, an upper trough to lift it, that's the recipe for Saturday's storms.

[c09_cape]

GUS Quickly on moisture first: dew point measures how much water the air is actually carrying, the higher it is, the muggier it feels and the more fuel a storm has. It's around 18 degrees here, decent for late October.

GUS Now the big one. Meteorologists measure the energy a storm can feed on. They call it CAPE, think of it like the petrol in a storm's tank. Oh, I love this one, it's basically the fuel gauge for a thunderstorm.

GUS About 100 kilometres south-west of Orange in central New South Wales, near Cowra, that stored storm energy is around 1,600 joules per kilogram by Saturday evening, a decent tank for this time of year, plenty to build tall, strong thunderstorms.

GUS The air also cools quickly with height there, nearly 6 degrees per kilometre, like a chimney with a strong draw, so rising air keeps accelerating upward once it gets going.

[c10_skewt]

GUS Think of a cap like a lid on a pot of boiling water: warm air sitting above the surface stops rising bubbles of air breaking through, even with plenty of fuel underneath.

GUS Here the cap is weak, only about minus 1 joule per kilogram, basically no lid at all, so storms can get going without much resistance.

GUS The air needs to rise only about 300 metres before it reaches cloud base, and then it's away.

GUS The trigger is that upper trough swinging through Saturday afternoon and evening, which is when I'd expect the first storms here to fire.

[c13_shear]

GUS Storms also need winds that change speed and direction with height, what we call shear, because that's what lets a storm organise instead of just collapsing on itself.

GUS Over this patch of country, wind speed from near the ground up to about 6 kilometres changes by around 115 kilometres an hour, strong shear.

GUS Picture a spinning top: a storm's own rotation starts out modest, but shear like this can tilt that spin upright, turning an ordinary thunderstorm into a supercell, a storm that rotates and can keep going for hours.

[c15_index_map]

GUS Forecasters combine energy, shear and rotation into index numbers. They're guidance about the environment, not a guaranteed storm, so I'll explain what each one actually means for you.

GUS The supercell value here is high, and the value for a storm that can start to spin is also high. Both point to a real chance of rotating storms, the kind we call supercells, rather than anything spinning down as a narrow violent funnel.

GUS The hail index there is high, meaning hail large enough to dent a car and crack a windscreen is possible, though not guaranteed.

GUS So, hail yes, maybe big enough to dent a car, and a real chance of a rotating storm, but these are odds, not a promise.

[c20_model_compare]

GUS Before I commit to a number, I check whether the computer models agree, because that tells me how much to trust the detail.

GUS Here, the American GFS, the European model and the European AI model all agree there's very little rain today, but they split further out: GFS wants about 10 millimetres over the next two days, the European model about 4 millimetres, the European AI model about 6 millimetres.

GUS That's not huge disagreement on amount, but it does mean I won't lock in an exact figure. The models agree far more on there being storms than on exactly how much rain falls.

GUS My own lean: I'd sit toward the lower end, around 5 to 8 millimetres, with isolated heavier falls under the strongest cells.

[c16_rain_wind]

GUS Let's run through the weekend in order, because hail and rotating storms come first inland, then things shift toward evening and overnight.

GUS First, Friday overnight: storms with a chance of hail, damaging wind and heavy rain over southern Queensland, about 70 kilometres north-west of Longreach, in grazing country.

GUS Saturday into the small hours, similar storms shift to the Gulf Country of Queensland near Normanton, the same district under that Severe Heatwave Warning, with damaging wind and heavy rain possible.

GUS Saturday afternoon, storms build near Charleville in southern Queensland, which has already picked up almost 17 millimetres of rain today and sits under that current Severe Thunderstorm Warning.

GUS Saturday evening is the main event, that rotating-storm environment we just walked you through.

GUS Sunday morning, the risk shifts to north-east New South Wales, about 180 kilometres north-west of Tamworth, near Narrabri, more about damaging wind this time than hail.

GUS Where the trough meets the warmest, moistest air, storms are worst there: large hail, damaging wind, heavy rain, and overnight they can join into one big cluster, a mesoscale convective system, which is why one town gets drenched while the next gets almost nothing.

GUS Typically 5 to 10 millimetres is likely there Saturday into Sunday, with isolated falls well over that under the strongest storms, and some spots missing out entirely. Don't lock that number in yet.

[c17_index_map]

GUS Now fire danger, the other active hazard today, because hot, dry air and strong wind out west are a different kind of risk entirely.

GUS Near Coober Pedy in northern South Australia, home to about 1,400 people, fire danger reaches a severe index of about 71 by Sunday morning, with the dryness measure near 10 out of 10.

GUS Temperatures near 32 degrees, humidity down near 15 per cent and wind gusts to 62 kilometres an hour add up to extreme fire behaviour if anything does start.

GUS They know the heat well, but a fire danger this high means even opal miners should have a plan and check for total fire bans.

[c92_river_gauges]

GUS On the flooding side, let's check how wet the ground already is and what the rivers are doing, because wet ground can't soak up more rain, it just runs off faster.

GUS Around Brisbane the ground is already very wet, about 105 millimetres of rain this week against a usual 18, while central Queensland, around Rockhampton, is drying out.

GUS On the rivers: the Bremer at Walloon is 2.06 metres and falling, the Logan at Yarrahappini is 3.09 metres and falling, the Mary at Miva is 3.57 metres and falling.

GUS Out west, Theresa Creek on the Gregory Highway is rising fast, up 3.7 metres in a day to 6.1 metres.

GUS That ground estimate comes from SILO data via the Queensland Government, and the river heights from the Queensland Government's monitoring network. None of this tells you if a river is in flood, for that it's always bom.gov.au.

[c90_events]

GUS A quick look at what's on this weekend, because several big outdoor events sit right in the path of these storms.

GUS Sydney's Sculpture by the Sea draws about 450,000 people this weekend, with a thunderstorm and lightning risk Saturday and gusts to 51 kilometres an hour.

GUS Victoria Derby Day at Flemington in Melbourne, about 86,000 people, also has a thunderstorm risk Saturday, with around 5 millimetres of rain and gusts near 49 kilometres an hour.

GUS Golden Eagle Day, Oktoberfest and the Halloween Festival in Sydney face that same storm and lightning risk.

GUS If you're at any of those, lightning means play and performances stop, bring something waterproof rather than an umbrella in the wind, and keep an eye on the organiser's updates.

[c22_town_table]

GUS Time for the lap of the capitals, beyond those weekend events, here's today's high and tomorrow's overnight low and daytime high, plus the rain, for every capital city.

GUS Sydney reached 22.6 today, tomorrow low 16.3 and high 27.4, with no rain, good beach weather clear of that Sculpture by the Sea storm risk.

GUS Melbourne's top today was 26.5 degrees. Tomorrow, low of 16.5 degrees, high of 22.6 degrees, with about 3 millimetres of rain across the city, on top of the thunderstorm risk already mentioned at Flemington.

GUS Brisbane reached 23.9 today, tomorrow low 17.8 and high 24.7, with barely half a millimetre of rain.

GUS Perth's top today was 20 degrees. Tomorrow, low of 14.7 degrees, high of 21.7 degrees, with about 6 millimetres of rain, grab a light jacket before you head out.

GUS Adelaide reached 24.3 degrees today. Tomorrow, low of 15.9 degrees, high of 19.5 degrees, with around 4 millimetres of rain, good news for the vegie patch after a dry stretch.

GUS Canberra reached 23.3 today, with tomorrow a cool low of 10.2 and a high of 24.2, staying dry. Hobart reached 19.3 today, tomorrow's low near 12 and high around 19.9, also dry, decent jumper weather if you're pottering in the garden.

GUS Darwin reached a sweltering 34.8 today, tomorrow low 26.4 and high 33.9, with about 8 millimetres of rain, hot and sticky under that heatwave warning, aircon earning its keep.

[c22_town_table]

GUS Now the week ahead, days two through eight, from a European model's nine-day rain forecast. This is a rain signal only, it knows nothing about thunderstorms or hail, so I can say wet, never stormy.

GUS South-east Queensland sees showers Sunday, Toowoomba the wettest around 9 millimetres, then drier before showers return midweek near Brisbane and the coast.

GUS Central Queensland sees some heavier falls Saturday, Rockhampton around 22 millimetres, easing after that. Northern New South Wales gets a heavier burst Sunday, Tamworth around 19 millimetres, which fits the storm risk I covered earlier.

GUS Victoria and Tasmania have a genuinely wet week coming, Melbourne, Geelong, Ballarat and Bendigo all likely to see 15 millimetres or more Saturday, again Monday, and again midweek. The Top End's heaviest signal is Thursday week, Kununurra around 15 millimetres.

GUS Confidence: days two and three are reasonably reliable, four and five more of a guide, and six to eight only a signal that can flip completely in the next run, because small errors in a model grow bigger every day. I'll update all of this tomorrow.

GUS Brisbane sees showers return Sunday, Sydney stays dry, and Melbourne picks up a little more rain. Canberra gets a proper soaking Sunday, with around 8 millimetres of rain as that trough swings through, making it the capital to watch most this weekend. Saturday evening is still the time to watch for storms inland.

GUS Looking further out, next Friday there's plenty of stored storm energy over south-east Queensland and the Top End but nothing obvious to set it off, so storms there could easily fizzle. Tuesday week looks more promising over northern New South Wales, where a trough arrives alongside that stored energy, worth watching, but it's still four days out, so check back.

[c01_verification]

GUS Quickly, how did I do yesterday? I check my own numbers against actual Bureau observations so you know how much to trust me.

GUS My overnight lows were close in most capitals, including Sydney, and I missed Perth by just over 3 degrees. Nationally my daytime highs were off by an average of only 1.65 degrees, better than either raw computer model I compare myself against.

GUS My overall confidence in today's forecast is high, up near the top of my own scale, built mostly from how well the three models agree on rainfall and on where that upper trough actually sits.

GUS What would change my mind: if that trough speeds up or slows down by even a few hours, the main storm risk could shift timing or move to a different stretch of inland New South Wales. I'll have an update tomorrow morning.

[c06_radar_now]

GUS That's the picture: severe storms building over inland New South Wales and southern Queensland this weekend, heatwave warnings in the north, and some rivers still falling out west.

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

GUS My next bulletin is tomorrow morning.

GUS If you've got a weather question, pop it in the comments and I'll get through as many as I can during the day. Thanks for watching.

GUS One thing to look for tonight if you're out west: watch the southern horizon after dark for distant lightning, that's often the first sign a cluster is building.

GUS Stay curious, and keep a brolly handy.

GUS Gus's Weather is a PandaVision production.