NSW - RAIN INCREASING WITH HEAVY FALLS DEVELOPING FROM MID WEEK WITH FLOOD RISK.

OVERVIEW

The dry is now behind us and we are now dealing with a steady increase in moisture, you would have noticed the temperatures have increased as well today and a warm and windy night is set to unfold for many over the south.


A day of increasing showery weather throughout the southeast of the state with local thunderstorms developing as well throughout the inland, this leading to persistent rainfall engulfing the Alpine Areas with those falls becoming heavier and more persistent with the risk of flooding developing as the snow melt and rainfall combine for swift stream and river rises.


Widespread rainfall will run up and to the west of the NSW ranges with moderate to heavy falls possible but not as heavy as the southeast areas.


Conditions will begin to ease during the weekend with showers decreasing and the westerly winds easing. Coastal areas will be spared the heavy rainfall this time around.


SHORT TERM

Next week we are seeing a general increase in moisture once again with the risk of heavy rainfall breaking out over parts of SA and WA. The question remains can that make it in by this time next week or will it be held out by the upper ridging in place that will give a fine start to the new working week.


The pattern though for the first part of next week is uncertain at the moment so keep watching the forecasts closely as we deal with the severe weather in the short term.


LONG TERM/AREAS TO WATCH

The longer term offers widespread heavy rainfall over large parts of the interior however, not all modelling is in support of this making the confidence rather low.


The trends are unchanged however, the impact of the Indian Ocean Dipole is becoming more apparent. The impact of the more favourable SAM lifting the strong westerly wind regime and the combination of the polar and sub-tropical jets, offer the chance of more severe weather events.


The northern tropics too, also in a state of early transition where we are seeing upper-level moisture levels beginning to increase, and this lifting heat levels. This too also increasing the atmospheric dynamics further downstream too into the south and east of the nation as we see the heat clashing with the colder air surging northwards. And with all the moisture floating about, we have seen on the GFS in recent days, things could turn very active very quickly if everything comes together.


WEATHER VIDEO PM - TUESDAY 2ND AUGUST 2022

FORECAST

Rainfall Next 10 Days

Rainfall is to become more widespread from Wednesday with showers developing over the southern and southeastern inland with local thunderstorms developing sparking heavier falls over the high country. Some areas could see some flash flooding issues already with the heavy rainfall activity. As we move into Wednesday night and Thursday, rainfall becomes widespread across all areas bar the far west and northeast/coastal areas. The rainfall heaviest on and west of the divide with localised flooding developing over the southeast, west of the divide. Local thunderstorms may also increase the risk of damaging winds with torrential rainfall also possible leading to significant flash flooding. The flooding issues will ease later Thursday over the Southeast of NSW and ACT, but the heavy rainfall threat continues on and to the west of the divide over the Central and Northern Tablelands. The rainfall will gradually ease during Friday with scattered showers left over as the flow relaxes and the low-pressure system weakens over the southwest of VIC. Showers clear this weekend and dry weather resumes next week ahead of follow up rainfall potential knocking on the door of the western districts from mid next week.

The heavy to very heavy rainfall over the southeast inland with the flood risks over the southeast increasing as the torrential falls impact the snow-covered areas of NSW and VIC. Areas around the ACT and points west need to watch the risk of severe weather over the coming days. Moderate rainfall throughout much of Wednesday PM through Thursday may not produce flash flooding generally, but very boggy conditions are expected to be found over the southern and central inland of the state. Heaviest rainfall the further east you go through the Plains and up the Slopes. Coastal areas should see drier westerly winds and this will spare the disaster zones along the caost.

Heaviest of the rainfall develops from Thursday into Friday with the higher falls on and immediately to the west of the GDR and then moderate to locally heavy falls along the plains, which is fluctuating in the guidance, but overall, the rainfall is expected to be somewhat above the average for this time of year. Coastal areas should be spared the worst of the rainfall.

Rainfall may be extensive under the cloud band through Thursday and Friday before easing as the band breaks up and the system to the south weakens, but the heaviest of the rainfall likely to be the further east you go through the state. A narrow band of rainfall will move through the Upper Western through SA and back to the NT, and if you get under that, it could be quite productive.

THUNDERSTORM FORECAST

Thunderstorms are forecast to skirt the SA and VIC coastal areas with the risk of strong squalls and the possibility of small hail as well with the main clusters of thunderstorms moving throughout the waters offshore. Another area of thunderstorms will develop along a trough over southeast NSW and northeast VIC with the chance of damaging winds and moderate rainfall, with hail a lower risk with the atmosphere very much saturated.

WEATHER ISSUES

Flash Flood Risk Tuesday to Thursday

The rainfall rates throughout the southeast and eastern inland of the state will lead to the risk of flooding developing throughout many locations later this week, especially over the area near the ACT and points west and through Alpine Areas.

Damaging Winds Risk - Tuesday to Thursday

Strong gradient winds developing throughout large areas of the southeast and southern coastal areas of the nation with the risk of destructive winds developing over higher elevation through VIC and NSW where winds may exceed 120km/h and 100km/h along areas to the south and east of the GDR. Winds will ease as the low weakens later this week.

MEDIUM TERM FORECAST

August 9th-16th 2022

Moisture Watch

It is very challenging to forecast the spread of moisture across the nation as it will be building throughout many areas but the relationship to the low pressure and the moisture remains the hot topic in terms of rainfall production. So, the arrows will appear once the confidence grows, but this forecast is of low confidence.

Rainfall Anomalies

Rainfall anomalies are bouncing around all over the place with the higher chances of above average rainfall to be found in the western and central interior, I have lifted it north of the coast but understand that it will continue to fluctuate as we see the pattern come clearer following this wild week of weather. Tropics certainly likely to see elevated rainfall emerge and it doesn't need to be much at this time of year to see green, but note the anomalies offshore in the island nations north of the nation.

Temperature Anomalies

The heat engine strengthening through the period, may begin to nose southwards but the divergence in the modelling surrounding the moisture and rainfall anomalies is also impacting the temperature anomalies for next week and into mid-month. So that is going to be playing a part in fostering the next wave of rainfall events from mid to late month as that warm moist air clashes with the colder drier air surging through the southern parts of the nation with frontal weather, but I have eased the temperature bias over the southern half of the nation due to uncertainty.

DATA - Refer to the video for further information and to put into context all the changes to the rainfall and temperature guidance through the short and medium term.


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

Please refer to the weather video at the top for further information and context relating to the large-scale weather event in the short term and a detailed look at the potential for follow up falls next week

00Z GFS - Precipitable Water Values - Next 2 Weeks

The moisture profile remains very much above the average as we track severe weather throughout the nation, and the elevated moisture levels will continue to drive the extensive falls across the east and southeast inland and the widespread falls pushing through the western and southern coastal areas will continue under somewhat seasonal humidity values.

00Z GFS - 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 rates over the coming 2 days over the southeast inland of the nation is expected to be equivalent to a 1/30-year event for Alpine areas with rainfall rates on a snowpack of huge concern. The rainfall further up the ranges and points west through NSW looking well above average. Rainfall in Victoria better over areas exposed to the northwesterly flow initially then shifting into a southwesterly bias over the weekend and that will be the case in SA as outlined for days and days and days on end. It is all unfolding as per normal. There could be some heavy falls leading to flash flooding over parts of the Adelaide Hills and that will be determined if the low pressure wafting around this week is closer to the coast. Additional rainfall is expected from this time next week.

More coming up from 8pm EST with a look at the models and rainfall.

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