The Australian Weather Forum

Progs are producing a big rainfall event with an easterly dip deepening and forming a closed low. The associated trough moves across Vic during Friday, with widespread rain and storms. Most models showing falls peaking at 50-100mm, though don’t agree on the details. Only model not so keen is GFS which splits the rain somewhat between southern NSW and Bass Strait. It still has ok falls, just not the big ones in the other models.

Should see first showers and storm develop later on Thursday, becoming widespread on Friday then clearing on Saturday.

Hmmm - I don't dare guess. For the last event, Ballarat was down for 'possible heavy falls' in the BOM forecast a day out, and ended up with 8mm (we got 4mm).

I do despair of model accuracy over the last month - for example, EC has gone from 11mm for Ballarat on Friday, to 51mm, in one run! And it's only 2 days out.

Any thoughts anyone on reasons for the consistently poor performance?

Gordon wrote: ↑Wed Jan 27, 2021 8:41 am Hmmm - I don't dare guess. For the last event, Ballarat was down for 'possible heavy falls' in the BOM forecast a day out, and ended up with 8mm (we got 4mm).

I do despair of model accuracy over the last month - for example, EC has gone from 11mm for Ballarat on Friday, to 51mm, in one run! And it's only 2 days out.

Any thoughts anyone on reasons for the consistently poor performance?

They've been very poor for many months - especially wrt precipitation. Partially due to much less input data from airliners apparently.

When I look at a forecast model I just divide rainfall by 4 for reality. If EC says 60mm, we might be lucky to get 15mm.

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They've been very poor for many months - especially wrt precipitation. Partially due to much less input data from airliners apparently.

When I look at a forecast model I just divide rainfall by 4 for reality. If EC says 60mm, we might be lucky to get 15mm.
[/quote]

This is from last March but would still be relevant.

https://www.ecmwf.int/en/about/media-ce ... -impact-we

Only model not so keen is GFS which splits the rain somewhat between southern NSW and Bass Strait.

That sounds about par for the course lol

Onetahuti wrote: ↑Wed Jan 27, 2021 9:13 am

They've been very poor for many months - especially wrt precipitation. Partially due to much less input data from airliners apparently.

When I look at a forecast model I just divide rainfall by 4 for reality. If EC says 60mm, we might be lucky to get 15mm.
[/quote]

This is from last March but would still be relevant.

https://www.ecmwf.int/en/about/media-ce ... -impact-we
[/quote]

Very interesting, thanks. I'd heard chat about this but seems it's a real factor. And I imagine southern hemisphere/ Australia-Pacific airline flights would be even more reduced than European/ northern hemisphere.

Imagine southern hemisphere more dependant on those sorts of inputs as well?

Meanwhile EC gone from 74mm for here on Friday to 87mm on 12z run. Will see,meanwhile wind finally moderating after a wild night and temp still only 13.8 despite constant sun.

Now 18z GFS has drunk the kool-aid and reckons 50mm here. Nope.

The system on Friday looks fast moving and maybe 25mm and if from Thunderstorm is more heavy like micoburst.

IF the system start pouring in SA and moist river cut off from NT then VIctoria get less.

La Niña and High Pressure Eastlery Dip is hopless.

and.... the latest GFS gives parts of northern Tassie 100mm + over the next week

And back to 12mm according to 00z GFS for here. That's more like it, none of this stupid 80mm on other models.

GFS only about 15mm here on 00z but Ukmet has upgraded further as has CMC to totals over 60mm. If this ends up being 10mm or so been a starring role by GFS. Wait for EC to continue the chuckles.

BOM upped Friday for here.

Friday 29 January

Min 16 Max 23
Rain.Possible rainfall: 25 to 40 mm
Chance of any rain: 100%

Humid. Cloudy. Very high (near 100%) chance of rain. The chance of a thunderstorm in the afternoon and evening. Heavy falls possible. Winds east to northeasterly 20 to 30 km/h tending north to northeasterly 25 to 35 km/h during the day.

Probably patchy rain between 1am and 10am Friday, before clearing. Similar to that of yesterday.

2 to 5mm in Melbourne metro

stevco123 wrote: ↑Wed Jan 27, 2021 4:49 pm Probably patchy rain between 1am and 10am Friday, before clearing. Similar to that of yesterday.

2 to 5mm in Melbourne metro

Stevo, your reverse phycology has worked a treat in the past !

dazrain wrote: ↑Wed Jan 27, 2021 5:12 pm

stevco123 wrote: ↑Wed Jan 27, 2021 4:49 pm Probably patchy rain between 1am and 10am Friday, before clearing. Similar to that of yesterday.

2 to 5mm in Melbourne metro

Stevo, your reverse physiology has worked a treat in the past !

One thing for sure is this easterly wind tonight will cause some damage. It always does down here

One thing for sure is this easterly wind tonight will cause some damage. It always does down here
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Yeah same will be a bit of carnage tonight around bayside
Wilsons Prom already gusting up to 80km/h
Great surf down that way..pity about the wind though

Like all of you I’ll believe 20-40mm for the CBD when I see it. For now I’ll just assume a huge downgrade will be issued at 4:20pm tomorrow, as is the tradition for the Melbourne metro BOM office.

Gordon wrote: ↑Wed Jan 27, 2021 8:41 am Hmmm - I don't dare guess. For the last event, Ballarat was down for 'possible heavy falls' in the BOM forecast a day out, and ended up with 8mm (we got 4mm).

I do despair of model accuracy over the last month - for example, EC has gone from 11mm for Ballarat on Friday, to 51mm, in one run! And it's only 2 days out.

Any thoughts anyone on reasons for the consistently poor performance?

Models alway have more difficultly in summer as rainfall is more convective with short time a space scales. Basically the bigger and longer lived an event is, the more straight forward to predict. I doubt the models have been any worse, but they definitely show a wide spread on recent convection dominated events. That tells you that the situation is complex and very small changes in details can make a big difference. Looking at this event, the progs range from 20mm (GFS) to about 80mm (UK and EC) here. That tells me that I’m mostly likely to see something in about the middle (so perhaps 40 to 60mm) but should not be surprised if it end up around 20mm, or I get lucky and get close to 100mm.

I’ve also found we tend to remember the exciting model runs the best. With Tuesday’s low I was expecting about an inch, and got 31mm. That’s pretty good imho.

Appreciate all a bit anecdotal There are hard numbers published, and I’ll see what I can find.

Progs continue to hold. GFS is the least keen. EC, UK, ACCESS and the EC ensemble are going off. Should see the first action develop for areas mostly west of Melbourne tomorrow. I suspect the stiff southeasterly breeze will keep storms out of the Melbourne metro but hope to be surprised very widespread rain and storms for Friday.

Btw check out the gradient in rainfall fractions for January. Suspect this explains a bit about how the season and models feel. It’s so patchy, and this is a really smoothed rendering.

hillybilly wrote: ↑Wed Jan 27, 2021 8:06 pm
Progs continue to hold. GFS is the least keen. EC, UK, ACCESS and the EC ensemble are going off. Should see the first action develop for areas mostly west of Melbourne tomorrow. I suspect the stiff southeasterly breeze will keep storms out of the Melbourne metro but hope to be surprised very widespread rain and storms for Friday.

Btw check out the gradient in rainfall fractions for January. Suspect this explains a bit about how the season and models feel. It’s so patchy, and this is a really smoothed rendering.

Well that explains why we are in a dustbowl atm.

I think GFS is taking into account that we are in a desert and is thus modelling rain to fall elsewhere.