NSW - BECOMING UNSETTLED FROM THE WEST THURSDAY.

The first in a series of troughs during the coming few weeks is set to bring a burst of showers and thunderstorms to the west and north of the state during the coming 24hrs, with the risk of severe thunderstorms for the Lower and Upper Western and extending through to western Riverina areas during Thursday afternoon.


A deep low pressure system developing over SA/VIC is likely to run along coastal areas of those states, it is close enough to add a bit of turn into the atmosphere so all modes of severe weather will be possible in the west of the state (refer to charts below the video).


I have made reference, eastern Riverina, ACT, Southeast NSW will see not much if any rainfall from this event at this time with the trough moving north, the low moving south and the region sits in diverging air. Isolated showers and thunderstorms can be expected in these areas at best.


The storm risk moves north during Friday and this could be a dangerous day of weather for parts of northern and eastern NSW with all modes of severe weather likely with thunderstorms.


By the weekend, things will begin to ease but from this time next week, another batch of strong to severe storms are likely to unfold with deeper moisture available, a more productive rainfall event is to emerge out of this.


Let's take a look.

FORECAST

Rainfall Next 10 days

Two rainfall and thunderstorm events sit within the window of opportunity for the state. The event coming through tomorrow through Friday and Saturday for northern areas, is expected to be modest, but some areas could score 20-30mm with thunderstorm activity. But generally most areas will see less than 10mm. The weekend turns dry and then another batch of showers and thunderstorms is expected to emerge from mid next week with a deeper moisture profile, this system has the potential to produce more widespread rainfall, some areas could see a month's worth of rainfall thanks to multiple days of showers and thunderstorms.

Thunderstorm Forecast Thursday

Thunderstorms are currently underway through SA and these will move into the far west tonight, they are high based and gusty, so some chance of damaging winds is expected along the far west overnight. Tomorrow, with the approach of the low pressure system, the trough over the far west will deepen and respond to better dynamics, showers and thunderstorms increasing over western regions, especially along the border of SA with severe weather possible. Thunderstorms may produce all modes of severe weather in the far west. A moist airmass may give way to isolated showers and thunderstorms elsewhere further east but no severe weather expected here until Friday.

Large Hail Risk Thursday

Thunderstorms have a moderate chance of producing large hail through the afternoon and evening, with that risk diminishing during the night as the trough and low pressure system begin to move slowly east. With the low pressure system diving southeast, the atmospheric dynamics will reduce a little for southern areas so the risk of large hail falls away.

Flash Flood Risk Thursday

Thunderstorms will trend from the middle level to lower level along the trough and with deeper moisture available, the thunderstorm activity will produce heavier rainfall. Rainfall rates of 50-80mm/hr possible in the southwest and west of the state.

Damaging Winds Risk Thursday - Related to thunderstorms.

Thunderstorms may produce strong gradient winds over 100km/h during the afternoon and evening, especially if thunderstorms form a squall line. Discrete thunderstorms ahead of the trough may also produce strong wind gusts.

Tornado Risk Thursday

An isolated brief tornado cannot be ruled out over parts of western NSW, VIC and eastern SA during Thursday afternoon.

DATA


Euro 00z - Surface Pressure Pattern and Rainfall Distribution - Next 10 days

The pressure pattern remains volatile and energetic at the moment with all the ingredients there for a disruptive spell of weather for those of you on the land from WA through to QLD and NSW. The SWLD has already received record rainfall for October (Perth surpassing it's record by nearly 30mm with rain still falling). The IOD is playing a part in all the moisture and thunderstorm impacts we have observed in recent weeks and that will persist for the next 4-6 weeks. So for those of you who have bought a few days of drier weather, which may persist into next week, make the most of it. These periods of drier weather with become hard to find as we run into the Christmas period based off all the data that I have shared in recent days and this morning and you can see in the data sets below that this is well supported. The system in the short term that has a high impact is the low pressure system that forms off SA tomorrow and moves close to if not over the SE of SA and Western VIC. Severe weather is a risk with damaging winds and heavy rainfall near that system, and whether that comes over land or stays offshore remains to be seen. The trough that accompanies this system will spark another round of severe thunderstorms on Friday and Saturday for NSW and QLD, with damaging weather once again possible for northern NSW and southeast QLD Friday into Saturday. So be weather aware. Large to giant hail and destructive winds are possible with that feature, more on that tomorrow. The next system coming in from SA next week comes with high humidity which may linger for 5-10 days into the medium term creating headaches for farmers with crops in the ground with higher rainfall chances and the risk of fungal issues. That signal has remained steady for recent days.

Euro 00z - Precipitable Water Anomalies - Next 10 days

No change from this morning and you can see the difference in the GFS in the video and the impacts that the variation in the postiion of low pressure systems has on rainfall and storm distribution. This will continue to be tricky to pin down under current circumstances (need more real time data to feed into the modelling - planes need to be back in the air!) But note next week how the dam wall breaks, the high moves out the way and the moisture surges south throughout the nation. Values are up to 300% of normal which is exceptional!

Euro 00z - Precipitable Values - Next 10 days

The warm shades of yellow and green is sufficient for extensive rainfall and thunderstorm activity throughout the southern parts of the nation. But to have values topping the red shading (60mm+) suggests that robust rainfall potential remains high into November and this won't be restricted to the tropics, but it will make it through the subtropics and into the southern and eastern parts of Australia. So be aware - if you have sensitive crops and plants. It is going to be bloody humid and feel a lot different to what it is right now through southeast and eastern inland areas where dry air has dominated this week.

Euro 00z - Rainfall Accumulation Next 10 days

It remains low confidence and really with the system coming through the southeast tomorrow, it may be a case of nowcasting rainfall totals, all dependent upon where the low pressure decides to travel. Thunderstorms elsewhere will bring uneven distribution of rainfall and that will be the case for much of the nation with no real organised rainfall event. We have another storm event to move into SA this time next week and the VIC, NSW and QLD later next week. That system will be slower moving than this feature and as I said above, tapping into higher moisture levels. For the west, you will see much drier weather with ridging. The tropics, most areas atleast seeing 20mm in the coming week, but many seeing much more!

A closer look in.

GFS 00z - Rainfall Accumulation Next 16 days

Refer to video for more

CMC 00z - Rainfall Accumulation Next 10 days

Refer to video for more

More details coming up on all things rainfall from 9pm EDT. Make sure you are logged in and can come back to the blog page for when that updates.

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