SA - SHOWERS AND THUNDERSTORMS INCREASING FOR THE EASTERN THIRD. DRY ELSEWHERE.

The trough over the border with NSW and VIC has been triggering large clusters of showers and thunderstorms in recent days. This trough is getting a bump to the west as the wind flow tends into the northeast. Those northeast winds also feeding the trough with showers and thunderstorms.


Severe thunderstorms are a reasonable risk in the coming 2 days with heavy rainfall the major concern from this current outbreak, though damaging winds and large hail over some of the east is not impossible and these could impact some of the vingerons out in the Barossa Valley and surrounds.


The weather will start to improve as we move into the back half of the week, with the drier and more stable air over the north and west spreading to the east and southeast with mild to warm weather continuing. The weather still mildly unstable near a new trough on Friday but overall the weather is set to turn drier as we enter the weekend, milder for the coast and above average over the northern areas.


Next week, there is evidence of moisture building out of the approaching MJO and this being drawn southeast into a large scale upper trough approaching WA. We may see a developing rain band out of that to our west but whether it comes through at pace and intensity remains to be seen.


Lets take a look

FORECAST

Rainfall Next 10 Days

Rainfall looks scattered about the east with isolated moderate to heavy falls possible with thunderstorms. The uneven distribution of rainfall is forecast to continue for this outbreak of thunderstorms. The weather further west is drier, but a few showers and thunderstorms are possible over these areas, but they will be hard to find so rainfall near negligible for most areas west of the Yorke Peninsula for now. As we get into the end of the week, another trough will pass through the south and southeast bringing a few showers and some local thunder. Clearing through the weekend with seasonal conditions but we are likely to see some increasing rainfall chances next week as a larger cloud band develops from the west and north of the nation as the MJO rolls into the eastern Indian Ocean and the SAM tends neutral heading back to positive. Should be interesting to see how that unfolds.

Thunderstorm Forecast Tuesday

Thunderstorms are forecast to continue about the east overnight and into Tuesday with the coverage creeping west throughout the day. Some of the storms may be severe, mainly east of Adelaide at this time, with heavy rainfall the main concern. There is a low end threat of thunderstorms developing west of Adelaide, less than 10% chance but too low to produce a chart for the region from the YP towards Ceduna. Something to watch and I will adjust the charts if required.


Flash Flood Risk Tuesday

Flash flooding with thunderstorms through eastern SA is the main concern on Monday night, overnight through Tuesday with the coverage creeping westwards during the day. Thunderstorms could drop upwards of 50mm/hr with the risk of flash flooding moderate to high east of Adelaide to the VIC/NSW border.

Large Hail Risk Tuesday

Large hail is a risk through the eastern areas bordering VIC and NSW during the day with the larger storm clusters. The risk is relatively low at this time but will monitor the risks moving forward.

Damaging Winds Risk Tuesday

Damaging winds are a risk through a large area of eastern SA but thunderstorms in this zone will be isolated to scattered about the eastern areas bordering VIC and NSW. So the overall risk looks quite broad but low at this time.

DATA - Refer to the video for further information on the daily breakdown in the short and medium term.


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

The confidence in the forecast is quite low as outlined in the video. Understand that the volatility in the SAM and the MJO being a little slower in recent updates means that moisture spreading throughout the nation could be out of phase with the frontal weather passing south of the country. But the GFS is on it's own in the short term when it comes to passing moisture later this weekend throughout the nation with a cloud band producing patchy falls throughout SA, VIC, NSW and QLD. So understand that this will change. Tropics look active and the weather over the FNQ region looks to be very wet near the persistent trade winds.

00Z GFS - Precipitable Water Values - Next 2 Weeks

Moisture distribution continues to be quite volatile from run to run, so there is difficulty in placing the moisture beyond the severe thunderstorm outbreak over the south and east of the country. So this will continue to impact the rainfall distribution as we move through the coming few days and so expect changes for southern and eastern parts of the nation. Over the tropics, you will find the significant moisture continue to kick off storms most days, with the heaviest moisture reserved for FNQ. Moisture does build offshore WA in the medium term but does that connect with the long wave trough building in the Southern Indian Ocean and bring in a large cloud band towards the end of the month? That remains to be seen.

00Z GFS - Rainfall Accumulation - Next 10 Days

Refer to video for further information

00Z CMC- Rainfall Accumulation - Next 10 Days

Refer to video for further information

00Z GFS - Rainfall Accumulation - Next 16 Days

Refer to video for further information

A closer look in - the weather over the region is highly conditional upon the SAM being in phase with the MJO and spreading moisture across the nation to be captured by troughs and low pressure that are moving west to east.

More details coming up looking at the models and all things rainfall from after 9pm EDT - we will see what the data sets are looking like for the medium and longer term and whether there is more rumbling about the Autumn Break that has been lurking on the charts.






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