The coverage on all social media platforms is going to be full of hyperbole and considerable. Most of you will have your radars up and therefore me telling you what you already know is pointless.
So when and where are the severe storms likely to form, and what are the mitigating factors to offset the severe weather risks?
Clearly the parameters for severe thunderstorms are high today, not off the charts, but certainly up there. There is ample shear, high levels of instability over the northern parts of NSW and southeast QLD on and east of a trough. Elevated thunderstorms have erupted this morning and that may mitigate some severity IF the cloud lingers along the coast. But with the dynamic support for robust thunderstorms and wind shear setting the convection into motion, it would be negligible to not forecast high impact. The best case scenario is that the lower atmosphere remains rain cooled and stable, but there are sufficient breaks over southern, central and northern inland NSW and west of the thunderstorms firing over QLD which has me concerned. All modes of severe weather remains forecast, I have outlined that in my forecasts this morning, no change on current data. Over VIC, it is sunny for Central VIC and low cloud about some parts of the west. Scattered to numerous showers developing later this morning with scattered thunderstorms from lunchtime, they will be slow moving and productive in terms of rainfall. Small hail also likely.
Current state of play.
Ares in yellow is the current convective shield, which is aiding in dampening down the atmosphere. So we want this to stay in place to keep the severe risks down, but as you can see on the loop at the top of the page there is clearance and breaks in the cloud further west of this morning activity. The warmer it gets the more volatile the airmass. If the storms break all at once mid afternoon, we will have significant problems ahead of the secondary trough in NSW and QLD, the risk is reduced over southeastern areas due to the colder weather and heavier rainfall than forecast. You can see the motion back in SA.
Dry cooler air is immediately on the western side of the trough, and immediately ahead of that trough is the warm moist air. We have ample wind shear that will send the convection into motion along the trough, which is where the most robust weather is likely. Remember the winds up above our heads is veering with altitude, so again the risk of all severe weather modes is high today, including tornado activity.
Regions of most severe weather as of 930am
Timing is uncertain with the rainfall ongoing over the east and southeast, again which will aid in dampening down the atmosphere somewhat, if that lingers then we may be able to lose the dangerous thunderstorm forecast, IF the cloud and rain is still there by 1pm this afternoon. Dumpers over VIC with small hail could also cause some issues for crops out in the Wimmera and Mallee. A weak tornado there is not impossible either, but generally non severe thunderstorms from SA through to the ACT.
Thunderstorm Forecast NSW and VIC- Thursday
All modes of severe weather is possible today in the east. A broad risk of tornadoes now is possible from eastern QLD through NSW, over much of VIC and near the centre of circulation over Ag SA.
Damaging Winds Risk Thursday
Winds are expected to be breezy with a gradient flow as the low pressure system begins to approach from the west overnight and into Thursday. The risk of damaging winds with thunderstorms is very high over eastern NSW and QLD where more energy will be built up in a warmer airmass. The risk tapers west of the trough and over the southeast where the atmosphere is more stable thanks to ongoing cloud and cooler stable air at the surface. Another wave of damaging winds will be ongoing through SA but will begin to ease during the day before heading into NSW.
Large Hail Risk Thursday
Large hail is a very high risk with the strongest storms in the purple zone. NOT EVERYONE WILL GET HAIL. But the risk is broad thanks to the dynamics at play. The rule of thumb, the warmer it gets the more unstable it will become, the higher the risk of hail with thunderstorms. Giant hail is possible over the northeast of NSW and SEQ. Small hail will be ongoing trough southern VIC and SA with cold air showers and thunderstorms.
Flash Flood Risk Thursday
A trough will lift deeper moisture laying over the eastern third of NSW which is where you will find the more robust thunderstorm activity, capable of producing rainfall rates of 100mm/hr. Storm motion will be modest so rainfall accumulation could exceed 50mm/hr in these areas. Lower risk in the morning over northeast VIC and southeast NSW.
Tornado Risk Thursday
Moderate risk of tornado activity over the eastern parts of NSW, more likely in the northeast and southeast QLD. 1 or 2 of these tornados could be longer track rather than a brief spin up. The turning in the atmosphere is supportive of this chance. Also brief low based tornados are possible about southeast SA and into western VIC with a low pressure system skirting close by. These will be brief and hard to detect ahead of time.
Riverine Flood Risk Friday and Saturday
Residual flooding over the northeast of NSW is likely to ease by the weekend. Up to 100mm has fallen this week. Over the southeast the main concern is to come, with a wrap around band of rain and thunder coming through on Friday and Saturday as a low moves to the southeast. Falls over 100mm possible.
Farmers and Graziers Warning
Cold blustery and showery weather with the passage of a cold cored low and trough over the coming days, leading to high impact weather to vulnerable stock in SA, VIC, NSW and TAS.