NSW - RAIN AND STORMS INCREASING FROM TONIGHT

The weather is certainly turning more active as we are heading through this evening with a band of rain and thunderstorms developing from QLD with strong to severe storms through the outback also producing some issues for remote communities. But most of this storm activity is forecast to spread a large band of rainfall through northwest areas and this will creep south and southeast through the state.


Widespread rainfall and thunderstorms are forecast to continue through Wednesday and Thursday as a moist airmass is lifted by this slow moving through. Some rainfall could be locally heavy leading to pockets of flash flooding and riverine flood issues.


Over the northeast, there is a chance of enhanced and excessive rainfall as we see a low form on the trough, but this may stay over in SEQ, but it is a line ball and careful monitoring of the weather over the next day or so is required as your rainfall totals in this region could be increased dramatically.


The rain and showers should clear the northwest and west during Thursday and continue over the southern and eastern areas into the weekend. A cold front coming along is forecast to lift all the moisture left behind from the first event into further moderate rainfall on and west of the divide before that clears by Sunday.


A cooler and much drier airmass will descend across NSW from Sunday and next week we should see much drier weather away from the northeast.


Medium term modelling has been showing more robust rainfall developments, but I will mention that this is low confidence and while the rainfall projections have been very high, it is signalling that there is the chance of more above average rainfall but the specifics of where is not quite clear.


Let's take a look at the very latest

FORECAST

Rainfall Next 10 Days

Rainfall is forecast to be the big feature weather wise over the coming 4 days with the rainfall locally heavy with thunderstorms and broadly moderate across the state through to the weekend for inland areas. There could be some very heavy totals continuing over the northeast of the state with some areas possibly seeing 300mm if a low-pressure system moves south into the state from SEQ Friday into Saturday. But the risk is moderate, and the forecasts here could change dramatically. Now as we hit the weekend, a front will sweep the moisture out of the state and a drier airmass will resume with seasonal conditions and showers contracting to the northeast. The next rainfall opportunities could once again be born out of the easterly winds resuming and another trough deepening over the southeast or eastern inland which could lead to more enhanced rainfall chances for many of us. A cloud band and moisture infeed over the northwest of the nation could also bring another band of rain into western areas.

Tristate

The rainfall over the coming 10 days falls now through to about Thursday or Friday morning. As per yesterday, treat the forecast here as a guide with thunderstorms in the mix making it very difficult to predict exact totals. The heaviest of the rainfall will likely be with thunderstorms but over in the east.

Southeast and ACT

The rainfall all over the shop in terms of the guidance. The rainfall increasing in the coming days with moderate to heavy falls developing along the slopes with the deep moisture leading to the above average rainfall spread. The rainfall over the eastern side of the Great Dividing Range is expected to be moderate over the course of this week with an inch likely to form.

Southwest Rainfall

Rainfall guide has been shifted back a little east but over the coming days. The rainfall could surprise in the coming days. However, in all zones with the thundery weather coming down from the north. Very tricky to forecast ahead of time but keep watch. The idea is the same, rainfall heaviest the further east and north you travel.

Central West Rainfall

Could see a little bit of divergence through the region where the moisture runs east and west of some areas along the Tablelands, which could lead to lighter rainfall being observed in the short term but overall, the weather for the region is looking wet and rainfall will be heaviest the further north and east you travel through the state.

Northeast Rainfall

Not much change for the coming days with a deep moisture profile and widespread falls expected. However, the wild card that could turn rainfall rates over the edge into dangerous levels will be the development of a low pressure system along the trough that could see a very heavy batch of rainfall coming through the region from Thursday into Friday. More rainfall develops next week.

Thunderstorm Forecast Wednesday

Thunderstorms are forecast to continue from later today and through Wednesday with heavy rainfall, possibly dangerous amounts of rainfall leading to life threatening flash flooding. Damaging winds and large hail are expected to feature with some of the taller storms along the eastern face of the upper trough. The main concern tomorrow is flash flooding.

Flash Flood Risk Wednesday

The heavy rainfall leading to flash flooding is the main concern with the highest risk over the southwest of QLD. That may move into the far northwest and drift further south if storm motion is ample. But areas to the north of Broken Hill need to watch the warnings very carefully through the coming 36hrs.

Severe Weather Risk - Remainder of Tuesday through Friday

The thunderstorms and showers are ongoing through southwest QLD and northeast SA today and this will extend over to northern and northwest NSW. The thunderstorms will bring the chance of flash flooding later today and into Wednesday over the northwest. Severe weather is possible over northern NSW and extending into the northeast of NSW during the remainder of this week and the threat is low to moderate. With excessive moisture values, I am concerned about rainfall rates being higher than what models are indicating in the yellow zone. So, expect some surprise heavy falls in some communities that are already dealing with wet catchments. It is a line ball for northeast areas north of about Coffs Harbour as to whether we see that really heavy rainfall comes south from QLD along a deepening low later this week.

Flash Flood Risk - Tuesday PM through Friday AM

Thunderstorms are forecast to emerge over the far northeast of SA and into northwest NSW and southwest QLD tonight with locally heavy rainfall likely to lead to flash flooding. The rainfall over the far northeast could also lead to flash flooding developing Thursday and Friday with a low-pressure system forming on the trough as that system moves through from the west. Rainfall remains moderate for much of far northern NSW in the coming days but there may be a thunderstorm that can produce a heavy downpour.

Additional Riverine Flood Risk - Wednesday to Saturday

The rainfall is expected to be excessive, mainly north of the border into QLD, but widespread moderate rainfall over wet catchments over the inland could renew some flood peaks along river systems that are already in flood over northern and northeast NSW. Some minor flooding is possible with a front and trough passing through the southeast of NSW and northeast VIC Friday into Saturday with moderate rainfall also to fall over wet catchments, on and west of the divide. The flooding from QLD will move downstream over the border into June and be with us through the coming few weeks and also move into northeast SA.

MEDIUM TERM - May 17th-24th 2022

Rainfall Anomalies

Rainfall signals for the northwest of the nation are increasing in response to deep moisture being propelled through the jet stream leading to areas of rain and thunderstorms becoming more widespread for WA. This moisture will spread throughout the nation, but the lack of strong trigger means that rainfall totals should be lighter through SA and into the southeast, however this could change if frontal weather is more in phase. Over the east, the increasing signals of a positive SAM phase developing through the coming week, this may lead to more above average rainfall for the eastern third of NSW and QLD. The risk of above average rainfall is higher over in the west this time around.

Temperature Anomalies

No change to the guide from yesterday with a warmer bias over the north with excess humidity in place leading to the chance of dry season showers. Cooler bias over in the southwest and west with persistent cloud cover. The warmer bias in the east is conditional and is based upon higher moisture levels leading to above average overnights and daytime temperatures, especially if the weather is drier than forecast.

DATA - Refer to video for more information and the model comparison and context about all the forecast products you see from me.


00Z GFS - Surface Pressure Pattern and Rainfall Distribution - Next 2 Weeks

More details can be found in the video at the top of the page but I will point out that the weather is forecast to turn more active over the coming days as advertised and the latest risks discussed there. The weather over the west also becoming more active in the coming days with a strong cold front moving through. Then that system could be moving through southern and southeast areas of the country. This system will help knock out the high moisture and severe weather risks over the east by the weekend and cooler weather resumes and a more seasonal spread of temperatures and rainfall can be expected next week. The focus of the wettest weather still looms over the eastern third of QLD and NSW in the medium term but more interest from me is in the west of the country, with a deeper moisture plume coming through the jet stream into the western and central areas of the country which could lift rainfall chances across the nation, WA, SA and VIC could fair better in this scenario.

00Z GFS - Precipitable Water Values - Next 2 Weeks

Widespread above average moisture levels are currently in place across much of the nation and entering the west of the country. It won't be until we see the western system move east, that it will help to knock out the deep moisture over the east and contract it northwards and then clears it away. Then we watch the persistent influx of moisture from the Indian Ocean and see whether that has some major impacts on rainfall rates over the west, southern and southeast of the nation as we move through into next week and the medium term. There are some weak rumblings for a large-scale rain event in the east which has been popping up on some models into the 21st onwards but I am not convinced of that just yet.

00Z GFS - Rainfall Accumulation - Next 10 Days

Refer to the video for more context and analysis

00Z CMC - Rainfall Accumulation - Next 10 Days

Refer to the video for more context and analysis

00Z GFS - Rainfall Accumulation - Next 2 Weeks

Refer to the video for more context and analysis

A closer look in - the rainfall projections are very tricky tonight when it comes to pinning down rainfall and you can make a case for any solution based off the varying differences in the modelling. Bottom line is, the further east and northeast you go through the country, the wetter you will be with the east coast trough. Disregard the second rainfall event that you can see in the medium term for NSW.

More coming up from 9pm EDT with a look at the models and rainfall, I will only share information that is in reasonable agreement as too much is too confusing and I only want to share what is plausible at this time, so stay tuned for that.



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