MODELS AND ALL THINGS RAINFALL - A LOT OF MOISTURE OUT THERE, SO WHERE DOES THE LOW PRESSURE FORM?

The models have been rather divergent of late, very tricky to pin down exactly who is going to get the heaviest of the rainfall, but that procession of moisture running from northwest through to southeast is underway, with the tropics now fuelling the rainfall across the nation for the next 2 weeks.


Lets take a look at the full suite. My ratings gives you an indication in my confidence regarding the data sets this evening and what is underpinning my forecasts.


SHORT TERM

Dictated by the movement of the ghost of Tiffany across the country. There has already been widespread heavy rainfall under this feature and will continue to be so for the next 48hrs. The moisture from the system then washes out into a broad easterly flow with a trough in the east, producing widespread showers and thunderstorms. The trough will then move west through NSW and QLD and link up with a trough over SA during the latter parts of this weekend and into next week producing rain and heavy storms. This will extend into the NT and maybe into the next tropical low developing over northern Australia. The location of that feature dictates where the rainfall spread goes.


UKMET - Rainfall Next 7 Days - MODERATE CHANCE

Showing that impulse of moisture coming down from the tropical north and from the unstable and moist northeasterly winds to feed the heavy rainfall potential for SA. The tropical low over the Arafura Sea moves into the Timor Sea and slows down. Moisture struggles to make it into VIC.

ICON - Rainfall Next 8 Days - LOW CHANCE

Moisture is a little further east than the UKmet but also agrees that moisture struggles to make it into VIC. Heavy interior rainfall. Has the tropical feature further west than the UK.

MEDIUM TERM

Moisture moisture moisture, absolutely everywhere but the models are struggling with where to place the low pressure in relation to the moisture so that is why you are seeing some large divergence in the guidance, and not exactly an easy forecast to prepare. But it shows you low confidence on who gets the best of it, but high confidence of there being a lot of rainfall about. This will refine with time.


CMC - Rainfall Next 10 Days - LOW CHANCE

Very heavy rainfall for SA and extending back to the tropics. IF this happened, that would be a year's worth of rain for some areas of SA in a sitting. I am not so sure on that but with the parameters as they are, it is not impossible. Heavy rainfall with a tropical feature sitting over the Kimberly Coast. Dry weather for VIC and much of NSW under tonight's guidance.

EURO - Rainfall Next 10 Days - LOW CHANCE

Has the moisture further inland through SA with some areas under this guide getting half a years worth of rainfall. Tropical system furthest west than any other model, of the Broome coast. That changes the flow of rainfall projections across northern Australia. More moisture makes it into VIC and NSW.

ACCESS - Rainfall Next 10 Days - LOW CHANCE

Access is similar to the Euro and places the tropical feature out west and has heavy rainfall stopping over SA and struggling to make it into the southeast and east however. Dry out west and stormy and humid over the eastern parts of NSW and QLD.

KMA - Rainfall Next 12 Days -LOW CHANCE

The KMA similar to Access and Euro, showing the moisture heaviest through SA, NT and over QLD. The tropical system is over the Indian Ocean rather than the NT.

GFS - Rainfall Next 16 Days - MODERATE CHANCE.

Most aggressive on the rainfall front for northern Australia, seeing the monsoon as a real chance of developing through this period. Has the tropical low passing over the NT rather than going west. Heavy rainfall for much of the continent under a slack pressure pattern dominated by troughs, moisture and easterly winds. The west is dry.

ENSEMBLE DATA

As always, the more reliable data sets are the broad ones, this offers more guidance from the larger sets as to where the higher probability of rainfall will occur and you can follow that with the shape and intensity of rainfall over the same regions.


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

The ensemble data is supportive and in line with the deterministic showing heavy rainfall sweeping the country with the chance of exceptional and record rainfall for some locations. Monsoonal conditions over the north and has the low pressure system on most members coming south over the NT.

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

In line more with GFS in the broader data set, many members take the tropical low over the NT rather than through WA. Has heavy rainfall for SA coming through via central Australia and moisture looks more likely to make the southeast and east under this guidance.

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

The Euro is more broadly wet than the deterministic over the nation.

LONG TERM

More rain for most of February and into early Autumn across the country.


CFS - Rainfall Next 4 Weeks

The wet phase indeed continues.....but note this has less rainfall than the data above so it is a significant risk of very heavy rainfall to come.

More to come from 830am EDT with your morning weather wrap. See you then.