It is the same ole boring line I am afraid that we have been watching since last Spring with widespread showers and storms for northern and central inland areas with increasing rainfall emerging along the coast, once again with a deepening trough along the eastern escarpment and the approach of an upper level low over inland regions this weekend.
The positive SAM phase at this time will lead to widespread showers along the coast but act to pump moisture into the unstable air sitting over the eastern inland - that means more robust rainfall is possible in the coming days or over the next week in this region.
For the western and southern interior, the weather is likely remaining dry for the coming 7 days in a holding pattern. That is leading to fine and mild weather, tending warmer out in the west with the easterly flow drying out and warming up as it runs over land.
The pattern will begin to breakdown later next week with some weaker signals for the troughs in the east to move northeast and east through to the Tasman Sea. Then we have the large high to sit over the southeast inland leading to a drying out of the state with sunny skies and warmer temperatures.
Once the high moves into the east and southeast, this will allow the door to open up for moisture and rainfall chances to increase from the northwest of the nation with some chance of rainfall returning to areas on and west of the divide, but this is likely outside of this period.
Lets take a look
Rainfall Next 10 Days
Widespread showers and a few strong storms over the northeast tonight will begin to ease but return through the eastern third of the state on Thursday as a coastal trough begins to develop. The positive SAM phase means that the onshore winds will feed the trough leading to moderate rainfall building with the persistent showers from the South Coast through to the Mid North Coast and adjacent coastal hinterland. Light falls inland along the divide with the odd heavier fall with the isolated thunderstorm activity. Thunderstorms become more widespread inland, especially north of about Orange on Friday and Saturday with moderate to heavy falls possible with severe thunderstorms possible near an upper low. The coastal trough also deepening with showers increasing further with moderate to heavy falls developing this weekend as the flow tends unstable east northeasterly. Some flash flooding is possible with the heavier onshore rainfall. The weather begins to clear from the northern and central inland early next week and the coastal areas from around this time next week with the new high finally moving eastwards. Dry weather for the most part most of this period but we could see some moisture return to the south and southeast inland later in the run, which could increase falls outside of this period into early April for southern and western areas that miss out for now.
Thunderstorm Forecast Thursday
Thunderstorms are expected to redevelop for a broad area of the inland but within that broad area, just isolated thundery weather is expected. The most concentrated thunderstorm activity is forecast to be over the northeast third of the state where the stalled boundary sets up. Thunderstorms could be severe in this region with heavy rainfall leading to flash flooding the main issue and possibly damaging winds with the low level jet still in the region.
Damaging Winds Risk Thursday
Damaging winds will be a moderate risk with thunderstorms that form over the northeast third of the state with the low level jet running at at about 60kts, some of those winds could be dragged down to the surface in this zone causing some tree damage.
Flash Flood Risk Thursday
Flash flooding is a moderate risk with thunderstorms that form in the northeast and along parts of the coast during the evening as convergent winds form near the coast. The most active risk will be found in the northeast third of the state with some areas recording 30-40mm in an hour. Some areas could see 20-30mm in an hour or two at night over the coastal areas from near Narooma northwards to Yamba.
Severe Weather Watch - Friday through Tuesday
Watching very closely the emergence of the upper level low moving into western NSW during Friday and how that interacts with the moisture and the existing trough sitting over the northeast of NSW and southeast QLD. Could see a rather expressive period of convection and given the dynamics, the chance of severe weather with storms is elevated over inland areas. Along the east coast, in east to northeast winds feeding the system, we could see heavy showers and flash flooding initially, and deepening on the rainfall coverage and the performance of the troughs together, there may be intense rainfall returning to parts of the coast. The most likely areas would be the extreme coastal fringe between Sydney and Yamba at the moment. The severe weather contracts into the northeast and east of the ranges by next week. The most active severe weather will be over areas south of about Chinchilla in QLD.
Riverine Flood Risk - Friday through Tuesday
The catchments are still very wet even though we have seen an absence of rainfall in recent weeks. The rainfall forecast will be moderate to heavy over a number of days and over time, the catchments will respond to this rainfall. Falls of 100-200mm are possible in the coming period in scattered pockets along the extreme coastal fringe and falls of 50mm an hour with thunderstorms are possible in all areas highlighted here. This may trigger minor to moderate flooding to redevelop along the coast. At this stage the amplification of the event is no where near the levels of the previous event but once again, riverine flooding is a significant risk for catchments devastated by the early March event. Remain weather aware through this region.
Flash Flood Risk - Friday through Tuesday
Flash flooding is a significant risk with thunderstorms with the upper level system moving in from Friday if not Saturday, into the moisture and stalled boundary over the north and east of NSW. The two will combine to bring scattered storms, some severe, with heavy rainfall leading to flash flooding a significant risk. From Thursday, there may be thunderstorms along the coastal fringe and streams of heavy showers floating about between Batemans Bay to Yamba that could see some coastal areas net 50mm in a couple of hours. Thunderstorms over the weekend across central, northern and northeast NSW could drop 30-40mm in an hour with the coverage contracting eastwards during the weekend into early next week.
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
We are still seeing the model madness from run to run and between weather agencies and this will make backing the right horse, hard to do. There are many people out there backing a model to bring them comfort, but the weather does not care about your intuition or what model has the best track record. These periods are low confidence for a reason and we have to look to the broader data sets and the observed weather to get a sense of where the weather is trending to be most active. At this time, the guidance on the modelling is suggesting the weather in the west is looking more unsettled over the weekend with severe weather potential from thunderstorms developing or with the passage of the remains of Charlotte and then a fairly moist and unstable airmass sitting over the western interior through next week. Over the eastern seaboard and into the GDR, the weather looking very wet with flooding become more of a concern as we move through the weekend and into next week with the positive SAM phase playing out over the days ahead. Over northern Australia, watching the evolution of the next tropical depression. This sits in one of the hardest areas to forecast tropical weather and will be very hard to pin down, but the rainfall and severe weather risks are increasing from run to run across most weather agencies. Over the south and southeast Australia extending back into the Central portions of Australia, the weather is forecast to remain dry and settled for about a week.
00Z GFS - Precipitable Water Values - Next 2 Weeks
The moisture profile continues to remain unchanged essentially from run to run, but what is changing in association with the moisture is the placement of low pressure which is what will drive rainfall. For now the driest weather near the upper and surface ridge over the central parts of the nation and extending through southeast areas and adjacent inland regions of NSW and into QLD. The wettest and more humid weather, in the west, western interior, through the northern tropics and over the east coast and coastal escarpment through to the dividing range with onshore winds via the positive SAM. We could see the weather shift during later next week as the high controlling the weather over SA moving into the east and then southeast of the nation. That may promote a deeper moist northeast flow lifting above average rainfall chances once again for NSW and QLD.
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 totals will shift around in the east. When you have upper level systems in play at this time of year, they can cause some rather high impact weather, but for now the confidence is low on both systems, in the short and medium term. Additional minor or moderate flooding is possible in the weeks ahead for the east.
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.