NSW - WARM AHEAD OF A THUNDERY CHANGE MID WEEK AND MORE RAIN THIS WEEKEND.

The weather has been pretty good the last few days, bit cloudy about the coast with not too many showers in recent days and the weather across the inland fairly pleasant though a few isolated showers have popped up in a mildly unstable airmass. That may continue for the coming 24hrs though conditions aloft through southern and southeast NSW are starting to shift, with the chance of showers and thunderstorms returning.


A weak cold front passing over the southeast of the nation is forecast to bring showers and cooler southerly winds to Victoria during Tuesday and into Wednesday. Along and to the north of this front, a weak cloud band is forecast to emerge in response to the temperature gradient playing out over the region.


With the cooler air riding northwards into the warmer more humid air, and the jet stream running through the region, we should see that cloud band emerge tomorrow through much of this week producing patchy falls to start with.


Now the trough that runs up the NSW coast mid to late week will pick up this moisture and we should see showers increasing Wednesday with local thunder, some moderate falls and that cooler shift moving northwards. Thursday and into Friday showers continue to be widespread over the east coast with local thunder but all eyes will then move to the inland.


An upper trough is forecast to develop over the interior of SA and move into the northwest of the state (at this time) and tap into the moisture streaming out of the Indian Ocean via the jet stream. We could see widespread showers and thunderstorms developing as a result with this separate system.


Over the weekend there may be a connection between the trough in the east and the deepening upper trough over the interior, leading to widespread rain and thunderstorms with locally heavy falls about. There is the risk of flash flooding and possibly renewed riverine flooding for some areas hit hard earlier this month about the east and inland areas through Summer. So that will be an area to watch.


Next week the showery weather looks to continue for the east but drier weather develops for the western and southern areas as the trough and low moves eastwards.


Lets take a look

FORECAST

Rainfall Next 10 Days

Rainfall totals are increasing for coastal areas with onshore winds developing from mid week and a northward moving trough through coastal areas enhancing the risk of thunderstorms. Some of those storms could be severe with heavy rainfall mid week from the Illawarra northwards and about the coastal escarpment. Showers to follow for the southeast and eastern regions, tending to areas of rain with moderate falls over central and northern coastal areas into the weekend. We have a moderate risk of an inland trough deepening over western NSW later this week which could spawn some showers and thunderstorms, the risk of severe weather at this time relatively low but there is increasing signals for rainfall to break out through Friday into the weekend. If the trough deepens over western parts of the state, then I will lift rainfall totals but at this time I will keep the forecast broad. The forecast remains at low confidence.

Thunderstorm Forecast Tuesday

Thunderstorms are possible over the southeast and running through the southern border with VIC as a cloud band develops over the region in advance of a cold front. Thunderstorms may be severe through VIC in advance of the cloud band and this could then run into southeast NSW later or at night. Heavy rainfall the main concern and damaging winds along the southern border during the evening but the risk is not especially high.

Flash Flood Risk Tuesday

Flash flooding is a low chance over the far southeast of the state with storms running over from VIC.

Damaging Winds Risk Tuesday

Damaging winds are a low chance and more contained over northern and eastern VIC in advance of the cold front passing through.

Large Hail Risk Tuesday

Large hail risk is contained at a low level to the elevated terrain over northeast and eastern VIC and possibly into far southeast NSW as the storms roll off the high country in the evening.

DATA - Refer to the video for further information and it is critical to keep check of the data sets to understand where the next major weather events are emerging from outside of this period. It may be quiet now but I am all about preparation and ensuring that information is shared with you as soon as it is available.


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

The GFS true to form indicates the weather turning volatile over vast areas of the nation but then is the one to pull back while other models now support the weather to volatile over western, northern and eastern areas. It is a common dance that I have seen in my 25 years of doing this. So at the moment, using the GFS, it carries a lower confidence that the other models which are more realistic of the impacts of the troughs over the east in line with the positive SAM phase (which is stronger than the previous event) so rainfall could be heavy at times over the east of the nation, more than what is being shown here. The weather in the west, is dictated by where Charlotte ends up travelling too, at this time, it does appear it is heading towards the Central West or Gascoyne. Now timing is the issue, we could have thunderstorms increasing in coverage from later this week into the weekend, but the GFS below suggests it could be slower on the approach and weaken the system offshore before moving it ashore with a trough and front. An upper level system still appears on other modelling for the eastern inland, but not on the GFS so that system while absent from the charts in the short term still carries a risk of evolving from the weekend with severe weather potential for the eastern inland. All of this weather bypassing SA and VIC where conditions should remain dry. Finally, the GFS still playing with an idea of a tropical low forming northeast of the Top End (other models have had this solution, the model dance continues) and this could produce heavier rainfall for the Top End and Cape York.

00Z GFS - Precipitable Water Values - Next 2 Weeks

Moisture remains unchanged from this morning. Moisture is forecast to sweep through the nation via the jet stream with a port of moisture running through the upper and low levels of the atmosphere leading to a band of rainfall spreading through the country, patchier this week over parts of SA but may increase through the eastern inland with another trough there. There may be another invigoration of the rain band over in the west with the moisture deepening as the tropical low approaches the west coast. Across the north, more of the same with deeper moisture and widespread showers and thunderstorms continuing as the MJO moves through. Drier air at the surface will likely be trapped under the ridge with little rainfall potential in this region for now.

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 - very low confidence in terms of rainfall beyond 5 days! Be aware of that.

More coming up from 8am EDT. There is little use of doing the models and rainfall wrap tonight looking at the spread. So will review that again tomorrow and update that element if required. 6 Week Outlook also due out tomorrow too.


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