EVENING WEATHER UPDATE - SEVERE WEATHER UNFOLDS OUT EAST. STORMS INCREASE TO THE WEST.

The severe weather has developed this afternoon over parts of northern NSW and southern and southwest QLD with a number of thunderstorms providing damaging to destructive wind gusts and heavy rainfall and flash flooding. One storm producing wild winds of up to 110km/h near Moree earlier this afternoon.


The trough to the south has been providing a mild light rain with up to 10-20mm in the bounce zones east of the divide in the southeast. Not much elsewhere other than a cooler day. To the north of the cloud band temperatures have been baking into the high 30s and low 40s in some parts of northern NSW, QLD and much of the NT.


Out west, an impulse of moisture is surging south into a trough that will bring an uptick in thunderstorms tomorrow with some of those possibly severe. More on that in the morning when the later data sets come in.


Severe storms will return to the east tomorrow with widespread rainfall. The rain over northern and northeast NSW into southern and southeast QLD could be heavy at times away from thunderstorms. The rainfall easing Monday. The storms will stick around.


The next major wave of low pressure arrives in the east from the central parts of the nation during Wednesday. That system may provide the eastern and northern areas of SA with some decent rainfall but once again clobber the east.


FORECAST

Rainfall Next 10 Days

Extensive rainfall signals remain in place, with at least 2 major rainfall events on the board nationally. We have the one unfolding right now with thunderstorms breaking out north of a weak cloud band over southern parts of the country. That storm activity north of the cloud band through northern NSW and southern QLD sparking the widespread heavy rainfall potential overnight and tomorrow for Ag areas in the east. The second event will emerge from a deepening trough and moisture plume through inland WA, this combining to produce widespread rain and thunderstorms over interior parts with locally heavy falls. That system will then move into the central parts of the nation and take the moisture over ever increasing tropics and pull that into the east and southeast allowing for another major rainfall event to emerge, this will probably be more widespread than the current affair over the east. Renewed flooding is possible for inland areas of QLD, NSW and a lower risk into VIC. The rainfall persists over the east in a deep northeast to easterly flow throughout the coming 10 days. Southern parts of Australia in a downslope and drying easterly flow will remain mild to warm and humid with limited rainfall opportunities being close to the ridge. The west dries out under the ridge mid next week.

STORM OUTBREAK

Thunderstorm Forecast Sunday

A deepening low pressure system over northern NSW will spawn showers and thunderstorms early Sunday and these likely to tend severe during the morning. Some of the storms may drop excessive rainfall in quick time leading to high end flash flooding, large hail and damaging winds in the red and purple zones. There will be scattered thunderstorms in a broad zone from northwest to southeast around this region with heavy rainfall and gusty winds also possible. Out west a new trough a deepening low will spark showers and thunderstorms, with some of those storms turning severe with damaging winds, heavy rainfall leading to flash flooding and large hail.

Thunderstorm Forecast Monday

Thunderstorms are likely to continue over the western interior from Sunday and increase again as the trough moves eastwards towards SA. Some of these may turn severe with damaging winds, large hail and heavy rainfall. The storm chance extends north up to the NT where thunderstorms may be gusty in the afternoon and evening. The east is where the most dangerous weather is likely to develop. Thunderstorms turning easily severe with heavy rainfall leading to flash flooding a very high chance with damaging winds also possible.

Thunderstorm Forecast Tuesday

Thunderstorms will contract to northern parts of the nation with a ridge sliding through Bass Strait into the Tasman. Easterly winds will continue to feed a trough over QLD producing scattered showers and storms, some locally heavy with flash flooding north of Hervey Bay. Thunderstorms may turn severe over parts of the Top End down to about Elliot or Lake Woods where damaging winds may develop.

Thunderstorm Forecast Wednesday

Thunderstorms are expected to increase in coverage and intensity from Wednesday with a deepening trough combining with northeast winds over the east. Thunderstorms will easily turn severe on and east of the trough with heavy rainfall leading to flash flooding the main issue from this far out. This forecast will be refined. Dry air over the west will clear much of SA later in the day with a southerly flow. Strong storms over the tropics may produce damaging winds near a trough over the base of the Top End.

THE WEATHER OF MOST CONCERN NATIONALLY.

Rainfall Next 3 Days

Rainfall is highly variable north of the cloud band tonight through Sunday and Monday, thunderstorms are expected to fire up near a developing low pressure system which will clearly provide the heaviest rainfall over central and northwest inland parts of NSW. The rainfall focus will be widespread over the GDR and in the northeast with coastal areas possibly seeing 100mm with convergence developing. The rain will clear the inland largely from Monday, though left over showers and thunderstorms are possible in a soupy unstable airmass. Next week more rain will develop from mid week, this chart does not include that system.

Thunderstorm Forecast Sunday

Thunderstorms are expected to develop early before dawn over northwest and central parts of NSW with some of these storms possibly severe with damaging winds and heavy rainfall. Large hail also a risk but more likely after the sun gets up and through the day time heating process. Storms will flatten out into an area of rain during the evening with moderate to heavy falls. The storms will clear the inland during the night.

Flash Flood Risk Sunday

Flash flooding a high to very high risk through central and northern inland parts with scattered thunderstorms. Some areas could record more than 50mm of rainfall in an hour. The focus shifts eastwards by afternoon and evening with a high risk of flash flooding along pockets of the coast.

Large Hail Risk Sunday

Large hail may develop with thunderstorms over the inland Sunday morning with strong storms forming near a low pressure system. The hail risk is conditional upon sufficient surface based instability through the afternoon and evening further north and east.

Damaging Winds Risk Sunday

Damaging winds are a threat with thunderstorms in the early morning and during the afternoon. The risk mainly on and west of the divide through NSW.

WESTERN AUSTRALIA

Thunderstorm Forecast Sunday

Thunderstorms are forecast to develop along a strong trough sharpening through the SWLD, Wheatbelt and Goldfields. Thunderstorms may be heavy with flash flooding and damaging winds. Large hail also possible during the afternoon and evening. Some of the storms may be heavy over the Darling Scarp east of Perth.

DATA


00Z GFS - Surface Pressure Pattern and Rainfall Distribution - Next 16 Days

A complex and volatile humid airmass over the northern and eastern parts of the nation is expected to be the focus of heavy rainfall and thunderstorms, with additional flooding. The west of the nation also seeing a complex pattern develop with showers and thunderstorms redeveloping with a deeper low pressure trough forming, this cutting off into another low, and heading into SA then deepening in NSW and QLD. So the better rainfall chances as mentioned remain the further east you are through the nation. This will remain the case in the medium term with a persistent easterly flow, the ripe environment for further low pressure to develop over the eastern inland, enhancing rainfall chances into December. There is very little break from the wet and stormy weather in the outlook.

00Z GFS - Precipitable Water Values - Next 16 Days

The values are going through the roof this week, coupled with temperatures in the mid to upper 20s in the east of NSW and QLD, rainfall rates will be quite high. The fuel from tonights thunderstorms is courtesy of the hot and humid airmass in place north of the cloud band. A low pressure system will form within the trough and utilise that hot and sultry airmass to produce the widespread rain and thunderstorms over the north and east of NSW into QLD. That will remain in place for the remainder of the period, as you can see the inland trough over the east, helps to dam that moisture for the period leading to rainfall chances most days. The tropics very soupy with above average rainfall chances, that moisture also feeds south, west and east into inland troughs over the temperate zones. The moisture from the Indian Ocean does not show any sign of letting up as we enter December. The lag of the negative IOD. Amazing how the forecasts in this country just could not see that influence.

00z GFS - Rainfall Accumulation - Next 16 Days

Extensive rainfall over the eastern parts of the nation is due to the short term low pressure but the signal that the onshore flow and low pressure will continue to operate in the east of QLD and NSW throughout this period, ending December 6. The tropical weather is anticipated to ramp right up this week, already an unstable northeast flow aloft has arrived a precursor to more substantial rainfall for the tropics. The southeast and south of the nation seeing mixed odds near ridging, with occasional bursts of humidity arriving before being knocked back into NSW and the interior of SA. The west, watch that impulse of tropical moisture in the short term. That offers heavy rainfall potential under thunderstorms and about the coast.

The persistent easterly flow with troughs over the inland is representative of the positive SAM phase and the ongoing instability over the eastern inland which is very normal for this time of year, what is not is the above average moisture content available, which will lead to heavy rainfall and flash flooding.

Heavy rainfall over the east coast is expected to cause flash and riverine flooding during the coming 2 weeks. Renewed flooding will also be underway through the inland of NSW, possibly northeast VIC with rain and thunderstorm activity in the short term and thanks to the persistent easterly flow that will establish in response to the positive SAM. Some areas inland could record 1-3 months worth of rainfall through this period.

That impulse off the coast is what is fuelling the above average rainfall chances over the coming 2 weeks across inland areas and will likely lead to an increase in tropical activity as well.

00Z CMC - Rainfall Accumulation - Next 15 Days

The ensemble data is also ramping up the very wet signal for the east and north with that bias being in place for the past week, but now intensifying as we get more clarity on the climate drivers. It is now being reflected in the rainfall forecasts.

00Z Euro - Rainfall Accumulation - Next 15 Days

Similar to above.

12Z CFS - Rainfall Accumulation - Next 6 Weeks

This is additional rainfall to come into early January.

More details coming up tomorrow from 7am. Have a great night.

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