MODELS AND RAINFALL - THE RETURN OF HIGH HUMIDITY AND WIDESPREAD RAIN IS IN SIGHT.

This period of drier weather will last another week or so before the nation becomes wetter and more humid, cloud cover increasing, to end what will be a hot spell over the coming week leading into Christmas.


The weather will begin to turn thundery over the northern and eastern parts of the nation first and then spread south from there.


Rainfall coverage is dependent upon the position of high pressure coming through Bight waters next week, the further south that ridge of high pressure goes, the further south the moisture will drift and where the moisture is, the rain will follow, especially with low pressure taking over.


Lets take a look


SHORT TERM

As mentioned multiple times over recent days, quiet weather overall. The areas to watch is the storm outbreak for the southeast mid week, another storm outbreak for the eastern inland this weekend along another trough. The rainfall over the tropics increases from later this week into the weekend and the western interior will see mainly light falls from high based showers and storms


UKMET - Rainfall Next 7 Days - HIGH CHANCE

No change to the guidance from last night. Coverage is light and patchy and connected to thunderstorms.

MEDIUM TERM

The medium term offers more rainfall for northern and eastern Australia as the next rounds of low pressure develops in response to the high heat this week. Hot air rises, causing air pressure to fall and that is what you will see in response. So by that, showers and thunderstorms developing from northern and eastern Australia and by Christmas it could be already unsettled and humid through parts of NSW and SA and then into the southeast towards NYE. The timing will bounce around and is dependent upon the high pressure cell south of the nation, promoting the easterly winds across the entire nation. Under such guidance, the far west of the nation will remain dry as will extreme southern coastal areas.


ICON - Rainfall Next 8 Days - LOW CHANCE

Too dry!

CMC - Rainfall Next 10 Days - MODERATE CHANCE

Tropical rainfall will be where the wettest part of the nation will be. Disorganised showers and storms across the nation from time to time with the troughs rotating through from west to east throughout the coming 10 days.

EURO - Rainfall Next 10 Days - MODERATE CHANCE

Rainfall numbers are also fairly set in place for the northern parts of the nation with increasing rainfall chances. The rainfall numbers are coming up for northeast NSW and southeast QLD later in the period attached to a stalled boundary and moisture feeding the trough. Relatively dry elsewhere which is the right solution, once we lose the westerly winds to the south, and easterly winds return, then coverage of rainfall from the north will begin to move south (refer to the broader data sets below)

ACCESS - Rainfall Next 10 Days - LOW CHANCE

Has backed off on the rainfall for the northeast and north which is probably right, the coverage of rainfall though moving south quicker than other models however, so will have to watch trends. Otherwise the thunderstorm activity is the main source of rainfall, that means it will be uneven.

KMA - Rainfall Next 12 Days - LOW CHANCE

This is bringing in the heavier rainfall chances across the nation, so for now this is a low risk, but this is what can be expected moving forward into the end of the month into January.

GFS - Rainfall Next 16 Days - LOW CHANCE

Still too dry against the broader data set. So still a low chance. Note the coverage of moisture comes south with storms making it into northern SA by the end of the period.

ENSEMBLE DATA

There is divergence in the broader data sets but the divergence is in how heavy does the rainfall get over the far north and how much of that comes south. The rainfall and moisture will seep south, the other question is, how quickly. These ideas to be ironed out by the end of this week into the weekend I hope.


GFS - Rainfall Next 16 Days (median of 35 members) - MODERATE CHANCE

As opposed to above, note the broader data set is still wetter and I do think we will see rainfall numbers coming up in the deterministic as we move along this week.

CMC - Rainfall Next 15 Days (median of 30 members)

I do think this is the right solution based upon the broader synoptic scale across all agencies tonight and the moisture building. With a cyclone on the board out east, models go a little haywire, until that moves away.

EURO - Rainfall Next 15 Days (median of 51 members) - MODERATE CHANCE

Also wetter than the deterministic data set and refer to the control below this.

Note the moisture does come south towards the end of the month and I do think that is the correct solution. Also watching for tropical mischief off the northwest of Australia as well.

LONG TERM

Still offering another wave of flooding rainfall potential for eastern, southeastern Australia and possibly through Central Australia, which is dependent upon the next impulse of moisture and once again where the low pressure sets up across the nation. There is a lot of moisture to work with.


GFS - Rainfall Next 5 Weeks - MODERATE CHANCE

As we move into January, the weather is expected to turn wetter across the nation but it is once again, dependent upon the return of monsoonal weather over northern Australia. When that occurs, then inland rainfall will come up. The return of a persistent easterly flow will allow for wet weather to increase along the east coast again.

CFS - Rainfall Next 6 Weeks - MODERATE CHANCE

This also supports the idea of a wetter as we go approach through January. Note the tropical tracks over northern Australia indicating the monsoon should return around mid month.

More to come from 7am EDT.