MODELLING AND RAINFALL - THE DIVERGENCE CONTINUES BUT SEVERAL HEAVY EVENTS ARE POSSIBLE.

The weather over the coming 2 days is fairly settled with troughs in the process of developing, one over QLD and another trough over WA. These will once again be the focus for rainfall over the nation tomorrow. The WA trough then broadens and moves east into SA and VIC with patchy rainfall and thunderstorms from Thursday.


A low will form on that trough passing over TAS with a weak change passing through the southeast during Friday. Scattered showers and thunderstorms may form over eastern NSW with that change moving up the coast.


Meanwhile a secondary low needs to be watched over eastern WA with rainfall increasing as it moves into SA, then into VIC and NSW over the weekend with locally heavy falls.


Another low will form over WA later this weekend and that too moves east into the central and eastern parts of the nation with widespread rain and thunderstorms developing next week.


Medium to longer term models keep the rainfall chances going through to early December with persistent humidity.


The tropics also turning very active.


SHORT TERM

As mentioned we have one major rainfall event sweeping through the nation from west to east with the best of it falling through southern SA into VIC and southern NSW and the ACT with local thunderstorms in the mix. The rainfall over the tropics also becoming more widespread later this week into the weekend with a trough deepening in the region and moisture returning. Another low pressure system is expected develop over southern WA during the weekend into next week with showers increasing and spreading east this time next week.


UKMET - Rainfall Next 7 Days - LOW CHANCE.

Does not render the rainfall event well and is completely different run to run

MEDIUM TERM

The secondary low moves into the central and eastern parts of the nation from mid next week into the following weekend with the position to determine where the heaviest of the rainfall will fall. The tropics remaining very active with showers and heavy storms. The west will turn drier under a ridge moving to the south over the Bight Waters. The rainfall over the eastern seaboard may persist as a broad easterly flow establishes. But as I keep mentioning it is a volatile pattern and your number will continue to change with a low confidence in the medium term.


ICON - Rainfall Next 8 Days - LOW CHANCE

Has the rain too far north for now on the lead system. Has the second system but develops it way later than other models. Too dry up north.

CMC - Rainfall Next 10 Days - MODERATE CHANCE

Has the rainfall spread right throughout the east and south and verifies the second system in line with other modelling. Most consistent from run to run....for now. Has the correct moisture profile up north.

EURO - Rainfall Next 10 Days - MODERATE CHANCE

Dropped the second feature. Has the first rainfall event with heavy falls over southern Australia but has shifted it further south tonight. It also sees the moisture over the tropics. I think it had the rainfall right this morning.

ACCESS - Rainfall Next 10 Days - MODERATE CHANCE

Very similar to CMC but has more rainfall for QLD and picks up the moisture building in easterly winds over the east coast. Hinting at the wildcard system over the east coast as well with a trough along the coast. Heavier rainfall for WA than the other models.

KMA - Rainfall Next 12 Days - MODERATE CHANCE

Has the similar rainfall spread to CMC and ACCESS with the first feature. Has more moisture than the other models coming in from the northwest of the country and over interior parts.

GFS - Rainfall Next 16 Days - LOW CHANCE

Too dry.

ENSEMBLE DATA

The divergence in modelling is much more clearly seen here and the one that sticks out is the GFS. It is unlikely that GFS is correct at this time given the current observations and I will lean towards the Euro and CMC solutions at this time as I have for the past few days. The consistency will get better from tomorrow night if not Thursday across models.


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

This is wetter than the deterministic data sets and has the east coast under a persistent easterly flow with rainfall increasing.

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

Probably the closest to the post in terms of rainfall potential. Numbers strengthening in the east like GFS and has more moisture coming down south and southeast from the tropical north over the nation to end the month.

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

A little too dry for interior parts but as per the other models strengthening the rainfall signals for the north and east into the medium term.

LONG TERM

Still have this very wet signal until the end of 2021.


CFS - Rainfall Next 6 Weeks

Note the monsoonal rainfall spreading south from Indonesia.

More to come tomorrow from 7am EDT.





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