Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  hillybilly on Sun Oct 04, 2009 5:24 am

Has been a strange 24 hours with persistent drizzle and light rain across lots of northeastern Vic. This is now spreading into south-centrals areas and looks like it should continue for much of today. There appears to be slight upslide into the upper trough over western Vic which is triggering the rain. Up to 11m at Benalla so some OK falls.

Looks the northeast and east-central areas will see the focus of weather today. Not a lot in it but a few mm are possible. EC has locally up to 10mm.

Longer term this event is starting to look better for Vic - though mostly a central/eastern Vic event. Monday/Tuesday/Wednesday look the best of it.

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Power Storm on Sun Oct 04, 2009 8:24 am

Now regarding thunderstorms, I would not rule out the risk for isolated afternoon thunderstorms over the western districts tomorrow afternoon, possibly extending into the central district as well. There is an upper trough that should move into the west during the early afternoon, but as this happens, a surface feature may develop over the same area, or a little further east, I think, if I am reading things right. The moisture levels are ok, and there does seem to be some growing instability from the west during the afternoon. If temperatures cool enough I think we could get some convection that could lead to isolated afternoon thunderstorms. Will have to keep an eye on that.

Monday looks interesting too re thunderstorm activity, I think most activity will be restricted to eastern parts as the trough moves a little east.

Tuesday looks active in the way of thunderstorms. I think we should see isolated to scattered thunderstorms develop during the afternoon/evening thanks to an upper feature and an impulse of moisture being available. Temperatures aloft seem ok too. So at this stage, I would say Tuesday looks like it will be good. Time will tell of course.

So above is what I said yesterday for today, Monday and Tuesday, and thing still look ok for today and tomorrow IMO, and was happy to see the BoM on board today as well for the possibility. See below...

--------
Australian Government Bureau of Meteorology
Victoria Regional Office

THUNDERSTORM FORECAST
Issued at 10:34 am Sunday, 4 October 2009,
Valid until midnight on Sunday, 4 October 2009.

An upper trough will move into western Victoria later this afternoon, reaching central Victoria Monday morning. Temperatures aloft are likely to fall by a couple of degrees in response to this. Meanwhile at the surface a weak trough of low pressure will persist near central Victoria today. Higher moisture levels are evident near the surface trough and with continued northeasterly flow east of the trough, moisture over eastern Victoria is forecast to increase. There will be a chance of thunderstorms over the southwestern part of Victoria this evening as the upper trough causes cooling aloft and destabilisation. Thunderstorms are also possible near and east of the trough this afternoon chiefly near and north of the ranges, however the threat is conditional on sufficient cooling aloft occuring. Should thunderstorms occur in any part of the State, wind profiles show modest speeds which would likely be insufficient to support storm organisation with the only severe weather threat due to flash flooding given very slow storm motions.

Australian Government Bureau of Meteorology
Victoria Regional Office

DAY 2 THUNDERSTORM FORECAST
Issued at 10:58 am Sunday, 4 October 2009,
Valid from midnight tonight until midnight on Monday, 5 October 2009.

An upper trough will continue to slowly cross Victoria during this forecast period. The trough will move from Central Victoria near dawn to reach the far east by evening where it will deamplify. Despite southwesterly surface flow extending throughout the State, sufficient moisture and surface heating is likely in the east to produce thunderstorm development on Monday. Thunderstorms are likely through the afternoon, however activity should rapidly wane during the early evening due to the loss of surface heating and the eastward movement of the upper trough. Shear profiles in East Gippsland ahead of the upper trough may be sufficient to support severe multicell or even brief supercell thunderstorm structures with attendant threat for large hail, damaging winds and flash flooding, however the threat is of insufficient magnitude to delineate an area at this stage.

---------
Could get quite interesting today/tomorrow with the trough about. Very Happy

EDIT: Looking at the BoM website this morning it seems as if the BoM in Vic have had trouble adjusting to day light savings ... Razz

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Anthony Violi on Sun Oct 04, 2009 1:58 pm

Nice area of showers over the eastern half of the state with very little steering...

BOM still sticking with good rain and very wintry conditions all week so be interesting to see where the Low positions itself..
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  droughtbreaker on Sun Oct 04, 2009 2:16 pm

There's been some towers around here and it's become increasingly cloudy this afternoon. Currently 8/8 cloud but showers refusing to form.

Interesting to see a S/SE airflow with heaps of showers forecast on Wednesday and snow down to 800m. Snow levels usually don't get that low with a S/SE airstream, normally it has to be S or SW. On BOM website state forecast says S/SW winds and Melbourne forecast says S/SE. I just don't understand how the system they are using can spit out such nonsense, we're talking directly contradicting forecasts for the same area. Rolling Eyes

If the models are correct and we do get a S/SE airstream mid week then I would assume that the western suburbs up to my area will benefit from the same bay stream effect that the eastern suburbs benefit from so often. (In fact I wouldn't assume, i know that this should be the case as believe it or not it actually has happened before if only around once a year or every 2 years. Rolling Eyes )

Of course I'll mozz the whole thing again, there will probably be a Tasmania block or something Laughing and it will be a total flop like last weekend was but i am confident this time around of some good falls here and the chance yet again of some decent snowfalls up Mt. Macedon. I was foolishly expecting a decent cover up there last weekend but the models are indicating an even better chance this week.

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Johnno on Sun Oct 04, 2009 3:29 pm

Hi DJ has EC tonight downgraded for the week? Looks to me it has in my eyes or am I seeing things? It seems to want to clear things quicker and the cold air doesn't look all that cold to me. GFS and UK still look reasonable to goodish for Melbourne and South Central Victoria

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Karl Lijnders on Sun Oct 04, 2009 3:35 pm

Looks like the showers could struggle up your way come Wednesday Andrew with quite a nice shadow from TAS in that SE stream. Hope the air is moist to carry convection. I am suspecting you may get frustrated.

The forecast is overcooked.

Expecting 5-10mm.
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Johnno on Sun Oct 04, 2009 3:39 pm

Johnno wrote:Hi DJ has EC tonight downgraded for the week? Looks to me it has in my eyes or am I seeing things? It seems to want to clear things quicker and the cold air doesn't look all that cold to me. GFS and UK still look reasonable to goodish for Melbourne and South Central Victoria

Incase you don't look onto the previous page DJ Smile

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  droughtbreaker on Sun Oct 04, 2009 3:51 pm

Models may be over cooked re. totals, but they are showing the SE stream in force with a spike of rainfall over the west central ranges, or at least GFS is. They wouldn't be showing this if the relevant mechanisms weren't in place, i.e. unblocked SE stream. Not saying there definitely won't be a Tasmania block, often there is, but current indications are there won't be with this system with the airflow coming in from around NE TAS rather than directly over the TAS landmass.

That Norwegian site which is EC apparently (ww.yr.no) for 00Z, seems to show around 10-20mm about the hills and ranges in central VIC and 5mm for Melbourne CBD on Tuesday, so similar to GFS.

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  droughtbreaker on Sun Oct 04, 2009 4:03 pm

Actually, Tuesday looks like a straight southerly to me feeding into the cold pool. Should be widespread showers, coming straight 'through the guts', won't struggle to make it here at all. After that, Wednesday is S/SE so really this should favour western suburbs and west central ranges. If the airstream is any more easterly it will favour more SW suburbs and Geelong through to Ballarat although S/SE looks a cert at this moment in time.

BTW, BOM were right on the mark with their thunderstorm forecast this morning. Very Happy

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Johnno on Sun Oct 04, 2009 4:07 pm

Latest EC totals... for CBD...

http://www.yr.no/place/Australia/Victoria/Melbourne/long.html

suprising its actually better than previous runs for Tuesday so im with the majority

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  hillybilly on Sun Oct 04, 2009 4:41 pm

I reckon this system is looking quite good for Vic (apart from the northwest). It won't be a drought breaker but 10-30mm looks pretty good for most. Of course, will be winners and loosers.

The key for decent totals will be warm air advection (into the upper trough - in other words low level winds winds blowing from high thickness values to low thickness values) and a decent easterly component in the flow to keep us out of the Tassie rain shadow - could see some very low snow in the first part of the event - certainly Mt Macedon and possibly even sleet about the tops of the Dandenongs. Tuesday looks the pick with very cold uppers, and upsliding southeast flow and rain periods.

Expect about 20mm up here in Ferny Creek - would not be surprised to see similar in the city. The biggest falls will be in the east, and I'd also keep a close eye on the western suburbs that could get a decent bay set up Tues/Wed.

BTW some handy falls in the catchments this arvo - 17mm at Baw Baw and probably similar totals across the Upper Yarra and Upper Eildon catchments. Had a heavy shower up here this morning, but brief giving 1mm.

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  droughtbreaker on Sun Oct 04, 2009 5:08 pm

Just looked at the Melbourne EC forecast again and it says 18mm for Tuesday so I read it wrong. This system is starting to look really nice now with widespread good falls progged just two days out and cold air. Very nice to see high totals progged for west central right through to east central and of course the east of the state continuing to get good follow up, that includes the catchments of course.

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Sniper on Sun Oct 04, 2009 5:39 pm

Firstly, well done John for sticking with this system!!!

Tuesday is looking like a very wet day. I will be happy with 10mm as long as others that need it gets some solid rains.

Any idea what temp the bay is, surely it is lower than normal given the lack of warmth so far! Will a colder bay temp affect show development in the SE flow?

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  droughtbreaker on Sun Oct 04, 2009 5:49 pm

That's what I thought too Sniper but it certainly didn't harm things last weekend in the SW airflow so mustn't be a problem there. The whole thing confuses me really, occasionally the bay effect can fail in the cooler months but most of the time it seems to be present IMO, even when the bay is cool. I'm probably wrong though in theory but that's just what I find happens. Eastern parts will get heaps of rain anyway regardless it just means the western suburbs through to here could get a bit of an extra boost with this system that we don't normally get (but is great when it comes off).

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Sniper on Sun Oct 04, 2009 5:57 pm

Bay temps can be found here, thanks to Mick who posted this link on WZ a while back.

http://www.earthsci.unimelb.edu.au/~awatkins/temps.html

Still chilly in there!!

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Karl Lijnders on Sun Oct 04, 2009 7:48 pm

Well i love forecasting rain when it's coming however US looks less inspiring again and I think being close to 24hrs out it is looking dubious however with useful showers where it counts if Melbourne gets 5-10mm which is what i'm expecting, it most certainly won't be a flop but I'm surprised with the level of optimism which is going on. Not that it's not acceptable just that it is funny how certain systems promote it.

Bring back cold fronts!!! Proper fronts!!!
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Malleefarmer on Sun Oct 04, 2009 8:45 pm

I reckon bring back those lovely troughs that come in and just sit for days over us with humid NE winds feeding thundery rain!

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Blackie on Sun Oct 04, 2009 9:36 pm

Nice bit of weather in Mansfield today with some decent showers and a great looking sky. I took some video of the Delatite arm of Lake Eildon and compared it with shots from a few months ago and last month. The lake rose 3%+ in the last week and the difference is dramatic.
Driving home through Flowerdale and Kinglake West tonight it poured.

http://www.youtube.com/watch?v=i32p3BK2t0Y

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Karl Lijnders on Mon Oct 05, 2009 4:24 am

Nice work B. Very useful rainfall in the region yesterday.

EC has downgraded somewhat and not shocked by that. The synoptic is not very impressive to me. US supports this but it doesn't mean it's over. Certainly a system worth watching but if you think widespread 20mm falls well that could cause frustration.

Still expecting 5-10mm but forecast suggests more. Looks overcooked still.

Today poses some interest out here.
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  hillybilly on Mon Oct 05, 2009 5:29 am

Agree Karl after ramping up its ramped down again.

Tuesday still looks very promising but totals look more like 5-20mm (best in the east) now.

The "front/wind change" is lying back along the west coast ATM and looks to be into Melbourne around lunchtime. Perhaps some showers and drizzle with it Question - could be some very low cloud on the front with Cape Otway showing near 100% RH with the change.

Still think we might scrape up to 20mm in Ferny Creek for the event.

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Karl Lijnders on Mon Oct 05, 2009 5:37 am

Can see a decent deck of low cloud to the west and south so could be a wet afternoon DJ for the region.

Heard the BoM sprook showers and storms for outer suburbs today though hmmmmm.
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  Karl Lijnders on Mon Oct 05, 2009 6:05 am

Nice early convection about. Looks promisng.
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  AmaroK on Mon Oct 05, 2009 7:33 am

Mostly grey out there at the moment, but the occasional patch of interesting looking clouds. Heres hoping we can get a few mm out of to day. Sitting just on 14 at the moment, but definitely does not feel cold out there.
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  I_Love_Storms on Mon Oct 05, 2009 8:51 am

Hi KL,

Do you expect much today?

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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

Post  AmaroK on Mon Oct 05, 2009 9:11 am

Looking at the satellite images, don't think there will be much other than a couple of light showers on the easter side of the state today, but the west could get a couple of nice ones this afternoon. Nothing major until tomorrow by the looks of it, but hell, this is Victoria, anything is possible right?

Also thinking temps might just fall short of the predicted max today, the clouds seem to be keeping temps down in a lot of places. only gone up about half a degree here in the last hour and a bit.
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Re: Victoria: (Possible) Low Pressure System and Thunderstorm Outbreak. October 4th-9th 2009

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