A week or two of wet weather ending Summer and kicking off Autumn is not unusual, but the coverage of rainfall under the La Nina climate driver plus the positive SAM will lead to above average rainfall potential for not only along the coastal areas on both states but for inland regions as well.
There are a few features to watch through this period.
An upper trough is expected to move out of SA through to the eastern inland of the nation, the colder air in the upper atmosphere then running into the very moist airmass that is in place leading to scattered to numerous showers and thunderstorms from tomorrow and through the end of the week, leading to the risk of severe weather potential.
As the upper trough moves further east it is expected to open up and wash out a bit, but it will still help to draw in the moisture from the Coral Sea and Pacific Ocean, so showery weather along the coast could become quite heavy at times in those areas exposed to the easterly wind regime.
Flash flooding from heavy rainfall from showers in the absence of thunderstorms is possible throughout the week and into the weekend. Flash flooding from thunderstorms through QLD and NSW and possibly dipping into northern VIC is also possible from tomorrow through the remainder of the week.
A fairly simple graphic overview of the mechanics in play to produce more rainfall across the country. For the east, it is watching the upper level low/trough over the eastern inland and how strong that feature is as it moves closer to the east coast where the onshore winds meet the unstable air to produce showers and storms inland and more frequent heavier showers along the coast. The monsoon trough up north will begin to influence rainfall chances over the eastern inland from next week.
Rainfall Next 10 Days - NEW SOUTH WALES
Rainfall is expected to be heaviest over the central and eastern inland parts of NSW and obviously along the east coast where the persistent showers will stack up to moderate to heavy rainfall accumulation. At this stage, the further west you go, the drier you will be which is a common theme when the winds are out of the east with significant drying of those winds expected as you head to the SA border. Thunderstorms over the inland will bring isolated heavier falls throughout Central and Eastern NSW with where they occur uncertain at this time but be aware that through this period, given the deeper moisture profile, flooding is possible with thunderstorm activity.
Showers are expected to remain a feature through the coming 10 days and with the approach of an upper trough, the likelihood of heavier rainfall is very high from later this week and through the weekend. There may be some locations record 200mm+ over the coming 10 days along the coast and adjacent inland. Inland areas on and west of the divide will see daily showers and thunderstorms, mainly through the afternoon and evening's with locally heavy falls mid to late week as the upper trough moves through from the west.
Drier easterly winds will see the rainfall rates dry out markedly through the region and no rainfall expected as you get into eastern SA.
Rainfall rates sharply drop off the further west you go through NSW and VIC, with some light falls expected along the SA border but you can see where the trough sets up along the Darling River.
Rainfall gradient is very tight from west to east with a deep trough over the western areas of the state. If you are living in this region, be aware that rainfall will vary with thunderstorms with some of you getting 50mm in an hour and others getting 25mm over the course of the week. It is the way it rolls. However it is a prolonged period of humid and thundery weather under this stagnant pressure pattern.
SOUTHEAST NSW AND ACT
Heavy rainfall for the east coast is quite likely and that will extend south into eastern VIC with a trough driving the persistent showers and storms inland and the coastal areas recording persistent showers and thunderstorms via easterly winds. The wet weather may peak later this week and again early next week. Flash flooding is a chance so stay close to forecasts. Rainfall may pick up over VIC during the weekend and next week.
Rainfall Next 10 Days - QUEENSLAND
The same trough over NSW will extend back over western QLD and tap into the developing monsoon trough over the north. Widespread showers over the east coast with increasing easterly winds with moderate to heavy falls possible during the outlook period. Some risk of flooding developing is a chance. Inland areas, showers and thunderstorms are expected to develop most days, near and east of the trough over western QLD. Storms could turn severe with some of the falls could exceed the monthly average in an hour. Flash flooding is a concern most days this week through inland QLD, but who gets the thunderstorm activity and who doesn't will change from day to day, but understand, the risk is broad under the current synoptic setup and that will persist into the weekend and next week.
Widespread showers and local thunderstorms most days through the coming 7-10 day period should bring an average of the rainfall displayed here for inland areas. Along the coast, persistent onshore winds with showers, locally heavy and gusty at times, will see rainfall totals accumulate in excess of 100mm in may areas along the coast over the coming 10 days but the falls will decrease as you head inland, but those areas inland could have convergent rainfall with storms moving out of the west, decaying and low topped showers running underneath that activity, bringing plenty of rainfall for areas inland of the coast over the coming 10 days.
DATA - COMMENTARY FROM THIS MORNING.
12Z Euro- Surface Pressure Pattern and Rainfall Distribution - Next 2 Weeks
Refer to the video to compare with the GFS, but clearly the wettest parts of the nation remains over the east of NSW and QLD, with widespread rainfall also expected over inland areas of QLD, NSW and dipping into VIC and through the ACT. Some heavier falls are possible with thunderstorms. The rainfall may also come into eastern parts of SA during the weekend with the trough moving back west ahead of a trough coming out of WA. That may see showers increasing this time next week over southern SA before more rain emerges through eastern Australia. Over tropical Australia, the weather is anticipated to be wetter as we go along. The monsoon trough is expected to deepen offshore and this could form tropical lows. Refer to the post on the northern monsoon and national impacts a little later today as models are all over the shop and all offer a wide range of solutions. The driest weather is still expected to be over southern WA extending back into Central Australia.
12Z Euro - Precipitable Water Values - Next 2 Weeks
The moisture profile over northern and eastern Australia is expected to deepen further as we go through this week and you will note the coverage of showers and thunderstorms increasing daily. By the end of the week, VIC, ACT, NSW and QLD through to the NT and northern WA will be caked under humid air, thick cloud cover and higher rainfall chances. The drier air will likely be dammed back over Central Australia and through SA and then into southern WA where upper ridging and drier southeast to easterly winds will be in place.
12Z Euro - Rainfall Accumulation - Next 10 Days
Can really pick up the trough over the eastern parts of the nation with a very sharp line through western QLD and NSW and anywhere on and to the east of the trough will see the rainfall, and next to no rainfall to the west of that feature. So watching where the trough stands up is important.
12Z GFS - Rainfall Accumulation - Next 10 Days
The east coast is very wet with heavy falls developing in onshore winds. Over inland areas scattered showers and thunderstorms will feature.
12Z CMC - Rainfall Next 15 Days
The broader risk of showers and thunderstorms over the east coast could lead to significant falls and flood potential.
12Z Euro - Rainfall Accumulation - Next 15 Days
Also supporting very wet weather over the eastern third of the nation with heavy falls leading to flash flooding.
12Z GFS - Rainfall Accumulation - Next 16 Days
Clearly a very wet signal over the eastern parts of the nation and thunderstorms will drive the heavy falls over the coming 2 weeks.
More coverage in the state based forecasts tonight.