Victoria - July 2001 Forecast Outlook, Discussion & Report Page



July 2001 Forecast Outlook, Discussion & Report Page Victoria
Date	Name	Information
.	.	Victorian Weather Glass
.	.	Check out the Melbourne webcam if you want to keep up with the weather in Melbourne.
29	Clyve Herbert	One of the largest cold pools I have seen this winter is playing about in the Indian Ocean west of Perth at the moment and moving east southeast, it will be interesting to see if the developing major low pressure system will drag moisture down from the tropics (lots of it there) and onto the Western Australian region. The sub tropical jet however seems rather weak to the north this seems to be a bit unusual for such a large system. Keep an eye on the JCU image for developments http://www.eng.jcu.edu.au/JCUMetSat/sector-c.gif
26	Clyve Herbert	An interesting clear slot separating two weather systems over Victoria at the moment, it will be interesting to see if there is any merging over the next 6 to 12 hours,also WA is looking better for potential rainfall over the next several days especially over the southwest corner it would be good for them if the present moisture plume extending from the tropics interacts with the approaching long wave trough and developing low pressure system.
25	Michael Scollay (NSW)	Conditions are shaping up right for a significant East Coast Low to form on Saturday centred about the North Coast of NSW. Now the SSTs are showing a pool of +2c anomaly warm water 500km off the coast much further south and +1.5C stretching down the coast. This could render the current model forecasts wrong in that they are predicting that the ECL will move off the coast and weaken somewhat. I'm hoping it won't but instead continue it's track down the coastline. If it does this, more cold air will be drawn up from the south "setting it off" like it did in 1998 when Wollongong got a drenching. As I said, an interesting "Day in the Life of the Weather" is before us for the filming.
24	Clyve Herbert	An upper area of complex vorticity can be identified near Mildura and just north of Mt Gambier this morning, unfortunately for much of Vic this area of upper convergence appears to be in the process of being pressure forced to the north east which is very good news for the east coast of Australia. The airmass over Vic though is conditionally more unstable than yesterday so we can at least look out for some congesting Cu and maybe the odd Cb!. There does appear to be some prospect for good rainfall over eastern Aus from this potential development especially when some of that warm moist Tasman air gets in under the mid and upper cold pool later today and tomorrow.
23	Clyve Herbert	Interesting to see cirrus (about 30.000ft) drifting from the north over central Vic this morning, (better than nothing) indicating a weak area of vorticity west of Vic, although a wish forecast it's worth keeping a check on. Also the baroclinic area over the Pilbara looks to be responding to an intensification of the sub tropical jet in that area may lead to a burst of patchy rain over that region. Interesting and large area of convection extending from about 10 north to near 10 south along the Indonesian west coast, it's already feeding moisture above 550hpa into the subtropical jet over WA. Also the active cold front south west of WA may aid in the transportation of this tropical moisture plume south eastward over the Australian region over the next several days.
19	Clyve Herbert	It's interesting to see the appearance of a third baroclinic mid and upper level cloud band in the northwest of WA - what is interesting is the development of scattered and unseasonable thunderstorms along the cloud development line over the sea northwest of WA along the entry level of the mid cloud deck and trailing downwind cirrus streamers.
17	Clyve Herbert	The strengthening of the high over SA and major cyclogenesis over the NZ area is allowing the development of a surge of proper cold air into the south Tasman and then onto the southern part of the South Island NZ, some pretty decent cold air CBs down there and what appears to be solid cold air at 500hpa. Invercargill looks to be the place to be tonight and tomorrow.
17	Blair Trewin	The Darwin Airport mean for July is 1.0mm (1.3 at the Post Office). They got 20.0 mm (not sure if this is a genuine 20.0, or a rounded one) to 0900 today. This gives Darwin Airport its wettest July day, and month, on record (previous record for both was 9.7mm in 1955). The Post Office has been wetter, recording 65.0mm in the period 1-3 July 1900, including 43.4 on the 2nd. To underline how rare such an event is, today is the first time since 1986 that more than 0.4mm had fallen on a July day at Darwin Airport. The (provisional) 95mm at Broome is equally extraordinary. It's clearly a July record for the site by a considerable margin; I'm currently running a job to check if it's the heaviest daily rainfall ever recorded in July in northern WA.
17	Clyve Herbert	Looks like Darwin will experience one of the rare winter rain situations for that region with the intensification of the baroclinic area across much of central and northern Australia. I think the mean rainfall for Darwin in July is less than 1mm (please confirm Blair.) Radar shows general 2-10mm/hr and some 10-20mm/hr patches, the persistent and active baroclinic area across Australia is interesting and appears connected with cyclogenesis around the New Zealand region.
16	Clyve Herbert	Interesting to see showers coming onto the northeast coast of the NT drifting from the north, may even see some get onto the north coast later today. All this is somewhat unusual, but the upper flow patterns there reflect and are connected to the reappearance of the large baroclinic leaf across eastern WA and SA.
14	.	ASWA meeting - Pancake Parlour, Doncaster. Guest Speaker - Greg Roff - Tornado Dynamics
13	Clyve Herbert	The airmass across the state is conditionally unstable with the risk of substantial showers in some places especially near the ranges and in the south of the state, may even be the odd spark, the only problem is the low amount of heating but nevertheless keep a lookout.
12	Nick Sykes	It looks like the easterly pattern that has dominated SE Australia for the past week will finally break down. A series of cold fronts will move through the SE from the weekend, with each front a little stronger. It looks like there will be only light rainfall totals with these fronts. They will pass through fairly rapidly and the air mass looks pretty dry. The SW winds following the fronts will introduce some colder air. By Monday, the strongest of the fronts looks like bringing some quite cold air, with GASP going for thicknesses around 563. Over the last couple of days it has been going for colder air, but seems to be weakening the system now, more in line with the other models that just have a more general front moving through. The introduction of some colder air should see the development of some much needed snowfalls, though because of the natural of the fronts, fast moving and short lived, I wouldn't expected big falls, just a top up. This period also looks to be windy, especially as the fronts move through, look for NW winds ahead of the fronts and SW winds behind. Looking further into the future it looks like SE Australia will remain in a cold SW flow until late next week with a very large high to our west. This high looks like it will be very slow moving and will bring a period of settled weather with cold nights and foggy and frosty mornings.
10	Clyve Herbert	The weakening low moving near to Adelaide looks like it will follow a northern track across Victoria over the next 12 hours and then combine with the remnants of the low off southern central NSW, then reform, this should be interesting for the southeast of Australia, again with showers some heavy especially in coastal areas from Victoria to central NSW, also a large area of cloud over New Guinea is also on the move southward responding to strengthening pre long wave north westerlies ahead of the upper trough over central Aus.
8	Laurier Williams (NSW)	Both this mornings LAPS and mesoLAPS have substantial precip (15-25mm) on the NSW NW Slopes, Plains and Tablelands tonight. The radar already shows a large rain area over and east of Moree/Narrabri. Given the cold conditions currently on the N Tablelands (forecast to continue) there could be some interesting snowfalls there tonight. It was 2.5 at Glen Innes at 6pm. I also wouldn't rule out a fall overnight on the Blue Mtns. 6pm temp at Mt Boyce was 2.1, and sinking like an anchor under clear skies. However, mesoLAPS turns the windflow gently onshore from late this evening, and radar shows showers east of a line running NE from Nowra. There have also been isolated moderate showers popping up all over today -- Forbes had 3.8mm, Parkes 3.4, Mudgee 4.2 and Nullo Mtn (Upper Hunter) 7.2 9am to 6pm, and the sky at sunset at Blackheath had remnants of Cb to the north and west.
8	Clyve Herbert	A marked thermal trough approaching the south west of WA looks to be showing some potential for cold season thunderstorms, especially from Perth southward, with the thermal trough lagging at 500hpa west of the cold front should see some warm advection from the surface to 850hpa under the colder temps at 700 to 500hpa. A feeder band now coming into the southeast corner of Aus looks interesting for the region between Orbost and Bega, may be some potential for local heavy falls in that. Also the sat pic shows Australia with a low affecting both the southwest corner (WA) and the southeast corner, looks better than what we have had over the past few weeks. PS: the large area of mid and high cloud moving towards the northern Tablelands of NSW also looks to have promise on the higher parts for some potential snow!
6	Nick Sykes	The problem for Vic is that the expected positioning of the low will see warm air been dragged in from the Tasman, while further north in NSW an Upper Level low (cold) will be sitting. It really does look like a win lose situation, with the northern resorts in for a chance dump while in Vic it looks like it could be far less. If it does snow in Vic, there is every chance that rain later in the systems evolution will wash it all away. This system continues to setup huge rainfall totals in Gippsland and the Southern NSW coast, flood advices have been issued.
6	Laurier Williams (NSW)	The models are still pretty mixed in their scenarios for the early weekend, which is when the colder air will get farther north, if at all. The latest EC keeps the 540 line around the Central/Northern Tablelands boundary in NSW, though has a centre of 534 around Orange on both Friday and Sat at 12UTC. The GASP 12z run also has a centre of 534 over Orange on Friday, and pushes the 540 boundary towards the Qld border, but slackens it all off by 12z Sat. Both US models are pretty marginal for snow away from the Alps, with thicknesses just below 540 and 850 temps just below 0. None of the models has much rain over NSW apart from the ST and SWS -- probably at best 5 to 10mm over the Fri + Sat. I have a gut feeling that snow and rain in this event will be determined by small-scale issues. The way the warm, moist air is forecast to wrap around the low that develops in Bass Strait on Sat and interacts with the cold airmass will be the thing I'll be watching. The models are having enormous difficulties with this low -- latest GASP (12z) has it 1002 off Gabo on Fri night and 992 over Melbourne on Sat night, EC moves it from 1004 at 500km E of Gabo Fri night to 997 on Mt Gambier Sat night!!! Yesterday's MRF simply has a trough on Fri from a central Tasman low to Bass Strait, but develops this explosively into a 990hPa low of the E Gippsland coast Sat morning, and keeps it there, slowly decaying through to +144hrs on Monday morning. From all this, I suspect that the developments in the area are a bit too dynamic for the models to be comfortable with, hence the variation, though obviously a major development is now highly likely.
5	Clyve Herbert	While the models are showing dramatic swings, my barometer is showing a slow and steady fall, which in the old days was said to foretell 'Long notice, long last, short notice soon past!'. Well this one is showing long notice!! We should treat models as sophisticated barometers and then keep looking at the sky.
5	David Jones	The damn models have done it again with the coming low system for SE Australia, and decided to change quite considerably from yesterdays runs. Instead of an intense low developing near central Victoria, with widespread sub 540 thickness values over the Victorian highlands/NSW (read heavy snow), they are now spinning up a much warmer low further north and east, to lie near the Southern NSW coast on Saturday/Sunday. The rather dramatic swings back and forth in the model predictions over recent days, suggests that much uncertainty exists in what exactly will happen over the weekend for those in the SE.... I guess the only safe bet is that some parts of the area will be subject to heavy rain, while most areas will be subject to strong winds. As for snow this could make the season, or leave us skiers waiting for the next system to fire things up......
4	.	Image of the developments in SA & the Bight today - courtesy Ben Quinn (ASWA - Qld)
.	.	Grafton radar loop (1410 - 1510 AEST) JCU IR movie (2nd & 3rd July)
3	Rod Aikman	With all the discussion about where the various models place low pressure centres, cold air pools, and wrap around cloud bands and the like; one thing I think is fairly certain: there won't be much rain in this system for areas of Victoria north of the dividing range, with the exception perhaps of the North Eastern district. There is a complete lack of tropical - extratropical interaction over the continent at present, and this will limit any significant prefrontal cloud band development. Extensive prefrontal cloud bands are essential with this type of secondary frontal wave low to produce significant rainfall over the interior ie. Murray Darling Basin. The only exception to this is if a low circulation happens to develop over Northern Victoria, and then cut-off; however I don't think this is all that likely.
3	Clyve Herbert	There has been a marked change in the atmospheric set up over south-eastern Aus over the past several days, the development of this system and its location will be critical in respect to where enhanced rainfall will occur, it's also possible for a surge of cold air to wrap around at some stage. It's also interesting to note a progressive westward motion of a region of cyclogenesis which over the past 3 weeks has favoured either west or east of New Zealand to near Victoria this Friday. Have you noticed the reverse upstream intensification process over the broad scale? at other times. Looks to be conditionally unstable over most of the eastern parts of NSW and southeast QLD, there could be some reasonable to decent CB developments over these parts today especially the northern Tablelands
3	David Jones	Of course, to keep us on our toes the new batch of progs have started coming in and these show some variations to the scenarios. Most notably, the UK is turning out a rather warm but impressive bomb for Friday, with a pressure drop (due to development rather than advection) of some 25hPa in 24 hours near Gabo Island (central pressures around 985hPa). Both GASP and UK now develop a strong warm and moist wrap around on the southern side of the low, with core thickness values approaching 550 gpdm near Bass Strait late in week or weekend. The cold pool associated with the lows is progged to hover near southern NSW through the event, with a quite remarkable baroclinic zone to its south with (for example) 850 hPa temperatures being around 8C warmer over Bass Strait/Tassie than southern NSW on Friday night. IF GASP and UK are right, this system could be a serious rain producer... in fact their would seem potential for a "very heavy rain" situation in the usual spots (Otways, south Gippsland Hills, NE Tasmania etc.) depending on the exact placement of the low and resultant onshore flow trajectories. As for snow.... it look bad for Tassie but probably very good for NSW. Victoria is anyone's guess?
3	Lyle Pakula (Colorado)	Looking at the SST's and the upper level trough forecast to come across, the models are producing a BOMB - rapid cyclogenesis off the East coast. Everything looks spot on and the system should 'stack up' off the east coast with a closed circulation right to 300mb. The system is forecast to cut-off from the main baroclinic flow with a strong ridge building and intensifying over the WA region. Considering the momentum that low is going to have, it's going to spin for a while, coupled with the high, I would not be surprised to see several fronts move straight up from the south over the next week or more, it's going to be wild! And for the storm chasers, it's all going to start with some possible cold air thunderstorms coming off Bass Strait with possible waterspout sightings definitely on the cards! Wish i was there... Back to the snow issue..there could be some seriously good snowfalls. I'd be looking for 50cm in Baw Baw and probably a little less in the central Vic alps. But this is only for the first wave of the system. If the cut-off low sits there and the high over WA cooperates, expect continuing snowfall, to very low levels, late this week and into next weekend (that's out past 144hrs). If this all goes, and judging by the ECMWF, there is a good chance that the long wave is going to cooperate, a storm total of 1m across most of the alps is definitely not out of the question. This would be a replica of the storm that dropped 1m+ in May 2000. Here's hoping everyone! For the pessimists who want to keep their feet on the ground, there are some modes of failure to consider. The 500mb vorticity looks good for cyclogenesis but it is 'thin' in that it could be hit or miss as to whether the surface low will form north enough to couple with the upper level trough. I only mention this to mention it. I do not think this is an issue at all and current obs already have the 'kink' forming on the leading edge of this cold front. Not to mention that the upper level motion seems to have been pushing nicely across the region to set-up for coupling. Rain could be a real issue for a day or so as the low intensifies but, again, i think this will only be an initial occurrence and cold air will swing through to keep the snow coming! All in all, this is a very exciting system and the forecast patterns are looking good for a very long lived snow event.
2	Laurier Williams (NSW)	The EC now agrees with GASP and MRF in predicting a moderately cold outbreak over Vic and NSW for late Thursday or Friday. The circumstances, however, are unusual, and there's a chance of snow along the eastern parts of the Great Divide in NSW, and possibly widespread in Victoria. All three models are consistent in predicting a low to form south of New Caledonia and east of Brisbane during Wednesday, then to move steadily SW to eastern Bass Strait by late Friday before shifting away to the E or SE. Meantime, a high in the Bight ridging SE will drag colder air up from around 50S over the southeast. Differences in treatment start to appear here. EC has a substantial cold pool with central thickness of 534 over about Young at 12z Thursday, then washes out to a broad upper trough lying from Adelaide to Brisbane around 542 by 12z Friday. EC drops the surface low to ~~990hPa just east of Gabo Island 12z Friday, then moves it slowly east and deepening on Sat keeping winds mostly SW over Vic and NSW. GASP develops 2 low centres by Thursday night, one south of Lord Howe Island, and another south of Adelaide, which have merged into a 994 low in eastern Bass Strait by Friday night. Consequently, the colder air tracks farther west and north, with a central thickness of 532 over Adelaide on Thursday night and 531 over the western Northern Tablelands of NSW by Friday night. Winds over Vic and NSW are mostly westerly, but GASP has 10 to 40mm of precip over eastern Vic and the NSW Southern Tablelands for the 48 hours to Sat night, and 5 to 15 up into the Central Tablelands. Snow hounds will be cheering on the local model! MRF keeps the low farther east and shallower, but still has Victoria and much of southern and central NSW sub-540 thickness by Friday morning. Precip totals are pretty light, however, in a SW flow. NOGAPS is similar, but doesn't develop a low centre; rather has a deep trough extending down the NSW coast at this time, and, like MRF, little precip. Significantly, none of the models has any SW or S jet development during the period, so it won't be a true polar outbreak as air will mostly be arriving from around 50S. However, the potential for interaction between the ECL and colder air at last gives us something interesting to watch.