NSW - RAIN AND STORMS BUILD FROM TUESDAY.

The weather is expected to turn from this evening, with already humidity and increasing cloud cover evident over northern and northeast parts of the state which is signalling the airmass change is underway.


The weather is forecast to turn more unsettled from tomorrow with a batch of showers and thunderstorms, some severe, developing over northwest NSW and then extending southwards into the Lower Western and Central West at night. Areas of light to moderate rainfall may also develop along the northern border and showers increasing for the northeast coast extending southwards as well.


The gradual sagging of rainfall from northern districts to the south of the state is expected to take shape through Wednesday with ongoing severe weather issues across northern and northeast parts of the state.


Once the trough begins to be nudged by the approaching cold front and trough in SA, the weather is forecast to ease from the north and west of the state as we head through Friday and the main rain event should be off the coast by Saturday.


A follow up front as mentioned above will move through southern areas later Friday with a band of rain with light to moderate rainfall at best, with a cooler westerly change moving through this weekend.


Next week, there will be showery weather may return to the northeast in onshore winds and another impulse of moisture is forecast to move into the west of the country along another trough with a widespread rainfall event possibly emerging from WA into SA then into the southeast and east, but the models as I have said for the past few days, hot and cold on this idea, but watch closely this week.


Better handling of that information surrounding that system will be available once we get this first major rainfall event off the board in the east.


Let's take a look

FORECAST

Rainfall Next 10 Days

Rainfall is forecast to become more extensive across the state from the north and spreading south as a deep moisture plume is lifted by a trough over the eastern third of the state and a deep upper low over the northwest of NSW and southwest QLD. Altogether, it spells we and thundery weather for many locations. The rainfall will eventually sweep south and southeast through the state this week with gradual clearance of the inland from later this week. Heavy falls leading to flooding is possible over the northeast and over the northwest with thundery weather. The flash flood risk is also elevated for many areas, particularly over northern districts. Another cold front passing through the southeast later this week will help to push the system and deep moisture eastwards and along that feature, a band of moderate rainfall is possible for southern districts. The weekend does look drier and much cooler with a stable airmass, but we will likely see the return of showers to the east coast this time next week with the potential of moderate falls redeveloping. Another trough is possible to move into the west of the state mid next week with further rainfall chances.

Tristate/Northwest NSW

Heavy rainfall will be featuring with thunderstorms and the rainfall gradient will be very tight so you could see a large fluctuation in the rainfall totals from one location to another, so use this as a guide. Some areas will absolutely be clobbered in this region, especially along the borders.

Southeast NSW and ACT

Areas of rain will approach the southern and southeast parts of NSW from about Wednesday into Thursday in a broad sense. Along the coast, showers are forecast to be present over the coast from later today through the remainder of this week. The climax in rainfall comes through Thursday and along a cold front moving in from the west on Friday with moderate to heavy falls possible. Rainfall is a guide and will chop and change and hopefully it gives you an idea of what is on the way for the region in a broad sense.

Southwest NSW

You can see that tight rainfall gradient with the trough and front linking into the deeper moisture profile that looks to stay more contained over central and eastern areas of the state, but reasonable rainfall is likely.

Central West NSW

Rainfall is expected to be widespread and moderate for the region, locally heavy the further north and east you go and the further west you go, the drier the weather will be, but this whole region looks to be recording another period of above average rainfall. With thunderstorms in the mix, your rainfall will be uneven in distribution.

Northeast NSW

The rainfall estimates are higher for some areas along the NSW and QLD coasts, but I am being more conservative given that the overall pattern is highly volatile and comes down to the placement of the convergent bands of storms and rain along the coast. For northeast NSW, it is a line ball to see the heaviest of the rainfall with this event. Some minor flooding is likely to unfold in the week ahead. Further rainfall is possible next week too.

Thunderstorm Forecast Tuesday

Thunderstorms are forecast to erupt over the northwest of the state during the afternoon and evening near a deepening upper low near the tristate borders. The thunderstorms could turn severe with heavy rainfall leading to flash flooding, damaging winds and large hail a risk as well. Thunderstorms will extend further south but likely weaken at night.

Large Hail Risk Tuesday

Large hail with scattered thunderstorms over the tristate region is possible during the afternoon and evening. It is a low to moderate risk for now. The higher risk is likely in QLD but expands during Wednesday

Damaging Winds Risk Tuesday

Damaging winds are expected with thunderstorms through the same region. Thunderstorms could produce damaging straight-line winds of over 100kmh during the afternoon and evening.

Flash Flood Risk (Thunderstorms) Tuesday

Thunderstorms are likely to produce heavy rainfall leading to flash flooding with slow storm motion, high moisture content and excessive rainfall rates likely in the current environment. Remember, it does not need to rain overhead for you to experience flash flooding in this location.

Severe Weather Watch - Tuesday to Friday

Not much change from last night with the risk highest at this stage over the northern third of NSW with severe thunderstorms causing the bigger concern around heavy rainfall and large hail, damaging winds over the region. The northeast carries the risk of severe flash flooding with any convergent bands of rain that develop later this week as the trough approaches from QLD. There may be a low-pressure system that forms on the trough as it advances east enhancing rainfall. Severe weather related to thunderstorms over northeast SA is a moderate to high chance from Tuesday through Wednesday afternoon.

Riverine Flood Risk - Tuesday to Friday

The low risk extends over into far northeast SA, northern NSW and into the southeast of NSW and northeast VIC with heavy rainfall developing in advance of a front passing through on Friday which could bring some minor flood potential over wet catchments.

Flash Flood Risk - Tuesday to Friday

The flash flood risk is broad and captures the broad thunderstorm risk over northern NSW during the middle of the week and areas of heavy rainfall developing and training north south over the same area for hours at a time, leading to flash flooding. The risk extends further south in advance of a cold front and trough on Friday into VIC and southern NSW.

MEDIUM TERM - May 16th-23rd 2022

Rainfall Anomalies

The SAM remaining at positive values should continue to pump easterly winds through this period with showery air and a moderate chance of further above average rainfall likely. With moisture streaming in via the jet stream, this could feed a trough over the eastern inland leading to widespread inland rainfall developing. That same cloud band and moisture plume may deliver widespread rainfall over inland WA with some moderate falls and the potential of this falling over the same area for a number of days. This rainfall may extend into western SA but the high pressure over the southeast may erode the heaviest of the rain making it through to Ag Areas of SA.

Temperature Anomalies

A very strong signal for above average temperatures and humidity over northern Australia with that warmer air extending southwards with northeast winds over the tropics. The east warmer than normal with a northwest to northerly flow early in the period but then that easterly flow with higher humidity will bring rainfall and milder weather. Cooler over the west of the nation under persistent cloud and rainfall potential. Near seasonal most elsewhere in white.

DATA - REFER TO THE VIDEO FOR MORE INFORMATION ON THE DAILY BREAKDOWN HEADING THROUGH THE SHORT AND MEDIUM TERM.


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

A very dynamic week of weather over the east and southeast plus out west with the break in the dry spell and warm weather there. More high humidity and unsettled weather is expected into the medium term as well with a deep moisture profile likely to link up with low pressure over the nation. The positive SAM phase if it emerges in the medium term could once again propel easterly moisture through the nation, opening the door for more heavy rainfall over QLD and NSW.

00Z GFS - Precipitable Water Values - Next 2 Weeks

Moisture levels are rising throughout the nation as the easterly winds propel moisture into an upper trough that is positioned through the interior of the country. The trough in the east is already lifting the moisture into widespread areas of rain over QLD and showers into NSW. The humidity will be lifted by the upper low over SA during Tuesday and extend that heavy rainfall risk right through QLD and into NSW mid to late week as the moisture is swept eastwards by the trough and front pushing through WA which too will have deep moisture attached. Note the moisture coming through the medium term via the remains of Karim coming into the jet stream. There may be some excessive moisture once again over the nation into the medium term, well above average moisture usually means we see well above average rainfall chances and that is likely once again as we track through the back of the month. So there is more potential follow up rainfall for large areas of the nation following the rainfall expected and high humidity over the nation this week.

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 comes in heavy in many locations this week with the upper trough over the east. Another event is likely to come through next week with another system in the medium term as well so there is quite a bit of weather for the second half of May on the way it appears.

I will have more weather information this evening and from early on Tuesday morning.








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