ASWA Victoria - April 2000 Forecast Outlook, Discussion & Report Page


Updated 1430AEST - 29th April 2000 - J ONeill
April 2000 Forecast Outlook, Discussion & Report Page ASWA Victoria
Date	Name	Information
29	Clyve Herbert	Update: marked pressure falls are occurring over SE SA & SW & central Victoria this morning. This may indicate that the trough approaching from the west may be intensifying which may result in stronger winds and the expected showers will probably remain scattered with isolated thunderstorms. Risks: possible vorticity along the frontal line may lead to cyclogenesis although this is a slight risk at the moment across SW Victoria. Also surface heating today across most of Victoria may add increased instability ahead of the appproaching front. If air pressure rises rapidly behind the front, it may indicate that a strong ridge is pushing across the head of the Bight as expercted. This will have a tendency to push low pressure systems to the SE.
29	Jane ONeill	Wildcard forecast (read yesterday's forecast first): A low pressure system was analysed at the surface this morning (7am) from a waving cold front in the northwest of the Bight. This system initially made its presence felt Thursday lunchtime in the 600-300hPa levels just of the coast of Perth. It should move ESE over the next 12 hours across SA & Victoria. Warm advection at 850hPa should mix down to the surface & keep the temperatures up in the mid to high 20's throughout the state this afternoon. Dewpoints are on the increase & strong to gale force winds and isolated showers with possible thunder this evening should make for a rather interesting night for Victorians. Get ready for the damage reports.....
28	Clyve Herbert	Okay, hands up all those who like high pressure systems!! Sydneysiders actually look for high pressure systems in certain locations, mainly in the south Tasman. Under these conditions it can drive in some serious showers from the Tasman. Personally I rather like the idea of this cousin of the Siberian high moving towards New Zealand, but knowing our luck in Victoria for the last 5 years it will probably amoeba its way right around the globe to reappear over Victoria in mid June! Anyway, back to more serious stuff......as expected, mid-latidude troughs and fronts have been peaking over WA. The West Australians been quite happy to rob us of our fair share of winter weather. It looks like this next set of cold fronts will move SE as they cross the SE of Australia. The first front should bring showers and patchy rain, mostly light falls, but several moderate falls are possible along the divide. The second front on Sunday should be accompanied by a belt of showers mainly in southern and mountain areas. The south Indian Ocean high is relatively strong and appears to favour a ridge towards the head of the Bight on Saturday and Sunday. Personally I'd prefer the ridge to move to the south of Tassie, but we can all dream....because if this occurs it'll cut off the current area of cold air and low pressure systems in the western Bight (this is a wish-list forecast!). Back to reality.... as this trough and series of cold fronts waffle off to Campbell Island, we'll probably be left to languish under a strengthening ridge across southern SA and northern Victoria Monday through to Wednesday. Thunderstorm prognosis: the 300hPa flow in front of the first front is not very cold, but there might be the risk of isolated thunderstorms on Saturday afternoon and night in western Victoria and along the divide & a very slight risk of a flash or two in the central district on Saturday night. Sunday looks a little better with the 500 - 300hPa temperatures falling significantly with isolated thunder possible with showers in the south and about the mountains. Regards, Clyve Herbert
27	Andrew McDonald	Neck-benders?? Hmmmm.....interesting Clyve, very interesting. Well folks, I think this weekend has some potential embedded in it. First of all I think we will see strong (possibly gale force) winds develop overnight Friday and into Saturday before the first front sweeps through as the pressure gradient increases significantly. Saturday seems like it will be a "run-of-the-mill" type frontal system where we will see cooler W'ly winds (also fairly strong) and some showers to follow. Sunday is showing a little more promise in terms of weather with a second front due. It is expected that the wind will shift around further to the SW and there should be some fairly unstable air following the passage of the second front. Cold air CB's are a possibility with 500mb temps possibly getting as low as -24C in the SW of the state. A fairly significant upper system will accompany this second front which again could make things more interesting. Current forecast charts show SW'ly surface flow of about 20knts and NW'ly 500mb flow (at a guess of 60knts) and NW'ly 300mb flow of about 100knts. I guess we'll have to wait and see what really happens but I suggest you keep an eye on the charts tomorrow and Saturday as there is potential for this system to get better (depending on which direction the low's finish up heading and how much they strengthen). Now going out on a limb. I think NEXT weekend we'll see another cold air system come through which has the potential to be fairly strong (and also the potential to dissipate to nothing). Keep watching the what's new page for a full and comprehensive report of Thunder Down Under '99 as I have finally got my act into gear and its on the way.
25	Clyve Herbert	Good morning neck-benders!! Congratulations to the BoM Melbourne for their models (whichever was used) for forecasting the strengthening high that has appeared over our region this weekend. Forecast was for 1037 last week and current pressure reading is 1036. This large identity (or atmospheric process) will move slowly eastward during the next 2 days and probably weaken slowly. Long wave trough W of WA should edge eastward. Troughs and cold fronts at the surface over WA should weaken as they move ESE away from the upper long wave trough. The likely scenario is for a progressive invasion of mid-latitude fronts across the Bight finally reaching Victoria towards Friday-Saturday. At this stage, these systems don't look too good for precipitation. Expect cold nights inland with isolated frost pockets in the south with potential for fog overnight tonight in southern areas. Wildcard: massive cloud area over Queensland developing under a strong sub-tropical jet which has been connected to cyclogenesis near the south island of NZ. Slight risk of vorticity within the 300hPa flow over Queensland with the risk of cloud areas moving south. This is just a slight risk. Happy Fishing!!
20	David Jones	It looks like the SE will get quite cold over the early part of the long weekend with snowfalls likely to quite low levels in Tassie (possibly as low as 500m), and possibly Victoria and NSW. 1000-500 hPa thickness values are progged to fall as low as 528 in southern Tasmania Friday night (suggests flurries as low as about 300m), and possibly as low as 536 in southern Victoria (flurries to about 1000m). Unfortunately for Vic./NSW precipitation will probably be on the lighter side.
17	Jane ONeill	Expect a low to form southeast of Esperance in the next 24 hours and move EESE (I think you get the idea - this is a few degrees south of east) to track through Bass Strait or across the north of Tasmania.
17	Nick Sykes	I am really liking the general pattern over SE Australia at the moment. The high pressure ridges are tracking further north and are weakening, this is allowing lows/fronts to the south to move further northwards. The front due tomorrow is showing some signs of forming a fairly decent frontal band, which could see some heavier showers embedded in it, some cold air behind it. 540 line forecasted near northern Tassie. Risk of snow in Tassie highlands. Front due on Friday is showing more potential, with a stronger high settling back to the west, and a possible low forming east of Tassie, colder air will be allowed to be pushed north. Watch this system.
17	Clyve Herbert	Hello weather enthusiasts! Hands up all those who got thunderstorms the last several days!! Down in Leopold I got 2 out of the 3 days with rumbles, but unfortunately only 3 mm rain. Some of you may have noticed that the middle and upper temperatures are very low. Together with troughs and fronts and relative low level warmth, the interaction with cold middle & upper layers has resulted in widespread scattered thunderstorm activity, some of which produced hail in Melbourne yesterday. While the Melbourne chasers were rubbernecking looking for more Cb’s after a very benign summer, we may look ahead to the forthcoming week. The south Indian Ocean High SW of WA is relatively weak, also the ridge towards the Bight and western NSW is similarly weak. This has allowed high latitude low pressure systems to wander equatorwards into the southern Bight area and to the south of Tasmania. We will probably see troughs and cold fronts drifting into SE Australia over the remainder of this week with interluding shallow high pressure ridges. There is some risk of a deeper low pressure system moving towards western Tasmania on Thursday / Friday. Overall, precipitation should be mainly light and in the south and mountain areas although Thursday / Friday looks better with the risk of moderate to locally heavy showers and isolated thunderstorms.
16	Dane Newman (Report)	Just saw some CC lightning followed a few seconds later by thunder, its been fine all day here although some good Cb's observed during the day in an unstable west to northwest airflow. Doesn't look like we will get any rain from the cell to the south as it is now moving away.
16	Debbie Parker (Report)	While Andrew was in Williamstown etc I was on the other side of the bay enjoying the spectacle. Saw a nice CG (around 14:20) hit the water just near Sandringham yacht club ('home' !!) with simultaneous thunder & heavy rain & winds that increased from around 10 knots to 25 knots in about 5 minutes. At about 16:00 or so another cell hit but I didn't get out taking photos until around 17:00 when I saw the next one heading right for me. I took a few shots from Picnic Point at Sandringham before moving towards Brighton - I got some nice shots of the rain curtain at sunset - little bit of mammatus on the leading edge - and managed to finish off the film & wished I'd had more!! Not a lot of lightning/thunder in any of them but great nonetheless.
16	Lyle Pakula (Report)	I was practically in the same area as Debbie. I'm wondering if, at about 4-5, you noticed the cell moving SE over Sandringham/Mordialloc start rapidly back building, just as its tail passed over the beach? The little cell over the far side of the bay was quite picturesque - no lighting spotted but with the sun setting and the big ships cruising in front view of the rain curtain - looked very nice. The mammatus you spoke of was the first mammatus clouds I had ever seen.
16	Chris Gribben (Report)	Didn't really take much notice of the day until about 1pm when I saw a mass of thick black cloud to my south. I got online and read a couple of emails about there being thunder as well as Nick telling me on IRC he heard some. I ended up heading out about 3.30pm to Doncaster Shoppingtown and filmed a few cells on and off for a while. The storms were high based due to the low DP. One of the lowerings I saw on a cell over about Malvern seemed to have rotation but it is unclear and the video I took of it will have to be studied to confirm this, it certainly wasn't approaching true wall cloud stage or anything. Caught a few decent CGs as well but missed a heap more. My interest then turned to a cell over Melbourne airport about 5pm. Saw some great CGs out of this cell but as it got closer it seemed to lose its strength. I left Doncaster to head home (about 5 mins - very handy <g>) and it started to rain the drops were very large and I was considering the possibility of hail occurring. As I drove through the rain there was an incredibly bright flash followed INSTANTANEOUSLY by thunder. There was literally no gap and the CG strike had either hit a power pole right next to my car or it hit the car itself! I was fine until about 10 secs down the road when it sunk in - hehe. Certainly an experience and by far the closet CG I have experienced or hope to. I was shaking slightly by the time I got home but the adrenaline was certainly there. I just wish I had got it on film or something somehow now. The strangest part of it was the fact the thunder wasn't very loud which leads me to believe that I was almost in the channel path of the strike. Anyone have thoughts on this? Anyone else got stories of close strikes? All in all a great day and fantastic to have such weather in April which has been boring for the last 5 years.
16	Nick Sykes (Report)	Woke up about 9 and had a look outside and automatically thought storms, that beautiful cloud was castellatus. Went on chat for a while but was in need of sleep so went back to bed. At midday I woke (I was planning on 1/2 an hour) and jumped out of bed to see what had developed. Was pleasant to see some nice pileus out to the west and a nice Cb to the east. I quickly checked radar and sat pic for the latest. Some nice cells were evident on radar and some nice cloud tops were evident on the satpic in the SW of the state. I decided I would head down the SE Freeway. Before I could do anything, my brother came and asked if he could borrow the car to get an oil filter, the one he had brought was the wrong type. So the chase was delayed. I spent this time drooling over the sounding which showed a very cold atmosphere as Macca has already mentioned. A nice cell came over my place early afternoon (green on radar) and dropped some very heavy rain. Heard some nice claps of thunder but saw no lightning Mid afternoon had arrived and my other brother had come over, so we decided to go out in my brother's car for the chase. At this stage we decided to head towards the NE out towards Doncaster. On the way a beautiful looking cell had developed to the NW over the city. The way we were heading showed little promise at this stage so we decided to head towards the city cell (was later to be found to be St Kilda with red). As we approached the features of the cell became evident. A very nice base with some ruffled scud. A well defined precipitation curtain had developed. We headed just shy of the main rain curtain to miss the worse of the rain, earlier in the day it was evident that any rain from these storms would be very heavy. That was all good and well we still got some very heavy rain. Didn't hear any thunder while chasing this cell. At this stage it was getting pretty late and my brother had to get home. Got home and that cell we had chased was putting out some nice rumbles of thunder, which goes to show it is very hard to hear thunder when in a car. Overall a very nice day, the main feature of today's storms would have to be the size of the rain drops, I have never seen them so big in cold air storm before. Radar of today's storms can be viewed here http://members.xoom.com/nsykes/radarapril16.gif and see my sat pic site for the sat pic animation. It can be reached at http://www.sesatpics.web.com/
13	Clyve Herbert	Brief update... Cold front & trough expected in western Victoria overnight & early tomorrow. Moisture loading ahead of this front is quite good. Good directional shear apparent over central Victoria this afternoon. ie: surface - 30deg backing to 260deg at 300hPa. Although the front is weakening, it should be accompanied by a band of rain with isolated, and possibly scattered thunderstorms. Risks: possible vorticity over SE SA & W Victoria Precipitation should mainly be light with possibly moderate falls in areas affected by thunderstorms. Front should continue to advance across Victoria, eventually crunching against the High in the Tasman (the front moving through the Bight and into SE Australia has been a good example of longitudinal (N-S) and +longitudinal (NE-SW) fronts). Thunderstorm forecast: air at 300hPa is sufficiently cold & lapse rate potential is moderately good. Isolated storms along frontal boundary, possibly becoming scattered at times. Outlook: ridging should push toward head of the Bight & western Victoria with the high becoming established in the Bight through early next week. Weak front should affect southern areas Sunday through Tuesday.
12	Nick Sykes	Friday is showing some promise atm. LI's are forecasted to be in the -3 to -4 range in northern Victoria on Friday afternoon (-1 to -2 in Melbourne). 500mb temps over central Vic are at -17and -44 at 300mb, which is nice. The models are also going for decent precipitation with this front, mainly on the northern slopes. The front moving across Victoria which should provide the lift to trigger some decent storms. Plenty of moisture in the lower levels after all the rain to our north. Front looks good atm on the sat pic but is forecast to weaken, hopefully it holds together long enough to give us some action.
11	Clyve Herbert	Hello weather enthusiasts!! Continued abundance of mid & upper level cloud over interior Australia appears to be moving SE associated with a strengthening upper level trough. This is good news for western & northern Victoria with light to moderate falls of rain developing in these regions tonight & tomorrow and extending into the central district, west Gippsland and the mountain regions later tomorrow and tomorrow night. At this stage falls appear to be light to moderate but will be useful in following up from heavier falls last week. The strong high in the Tasman will remain slow moving and will maintain above average temperatures throughout this period directing mainly NE to E flows across south eastern Australia. This rain area should pass to the SE and weaken Friday however a mid latitude trough and associated cold front should reach Victoria Friday night with further patchy rain and isolated thunderstorms followed by a colder southwesterly airflow. Risks: the large area of cloud moving from Central Australia to SE Australia may be associated with the development of a low in NW Victoria tomorrow. If this occurs, precipitation will be heavier. This is however, only a slight risk. At this stage, the cold front due on Friday night in Victoria may weaken as it crosses the state. The high pressure area should push into the Bight on Saturday. Thunderstorm forecast: the disturbance moving into Victoria on Thursday is associated with more stable upper level conditions. The stability appears a little too high for major storm activity at this stage. Isolated middle level thunderstorms are possible with this system particularly in western & northern areas. (interestingly, the upper layers remain rather cold at 300hPa). The prospect for thunderstorms on Friday night is a little higher.
9	Andrew McDonald	From what I've seen, most models are forecasting a surface low to form on or near South Western WA by Tuesday. Most models also forecast this low to intensify pretty rapidly. I'm interested in the effect this low could potentially have on SE Australia (especially SA and VIC) come Thursday/Friday. First of all there is potential for this low to produce some severe weather in far SW WA in terms of cold air supercells (high shear & low buoyancy) but as I don't know this area and how weather systems behave so this is a somewhat uneducated prediction. The effect this low will have on the SE states depends hugely on the movement of the system. Some models have this low heading SE so that it eventually passes S of Tassie. Generally, what usually will happen is that the low will spawn at least one (if not more) troughs/fronts which will extend northwards. If the low does move SE I think we will see one of these troughs extending into SA and VIC and depending on the moisture content of the middle layers we could see either a fairly substantial rain band or a line of storms. The storms (if it happens) could be very very nice with 500mb temperatures of -18C in most of Victoria and -20C in SW Vic forecast. NGP actually has this low pressure system heading almost due E. This would create amazing conditions in Victoria on Thursday and Friday with very strong winds, rain/storms and then very cold weather come the weekend. It could be a very interesting second half of the week in the SE states but I think we will have to wait until Tuesday before we get a better idea of the intensity and movement of this system. I am also interested in the cold air which is likely to be dragged up by this low pressure system. I think we could see our first real cold outbreak in the SE states by the weekend. Some models have the 540 line (thickness) steadily heading N of Melbourne by Saturday with the 528 line not all that far S. This cold outbreak has been on the cards since early this week and while I think it will be scaled back a little later in the week, we should still see our first decent snowfalls on the alps and some cold air CB's and possibly hail showers in Melbourne. This system could change Victoria's April severe weather hex. We haven't had a reported severe weather event in April since about 1995 (this could be wrong but I can safely say that April has been our most boring month in terms of severe weather in a long time).
9	Clyve Herbert	Weak trough in western Victoria. Potential: isolated thunderstorms & rain patches moving SE. Remaining warm. Interesting aspect is that the 300hPa temperature is still <-42C.
9	Jane ONeill	AREA FORECAST 082300 TO 091100 AREAS 30/32 PATCHY RAIN DEVELOPING N OF LAMEROO/BALRANALD WITH ISOLATED THUNDERSTORMS IN THIS AREA AFTER 05Z. ISOLATED SHOWERS DEVELOPING W BORDER AND EXTENDING E TO 144E BY 05Z. TROUGH TO W EXPECTED NEAR MILLICENT/WEBS 23Z, BORDERTOWN/COLAC/HUNTER ISLAND 05Z, BORDERTOWN/ WATSONIA/YARRAM 11Z. LOW CLOUD PATCHES SEA/COAST W OF TROUGH. Mildura is a forecast probability with 50% chance of storms between 3 & 6pm, and there are already congesting cumulus in the NW of the state. Swan Hill webcam is showing sizeable cumulus for this time of day (and year). Temps over Melbourne last night were: 850 9.8 500 -14.7 300 -42.5 Fairly dry through its depth over us last night, but we have an infeed from the north of moisture at the moment which should improve the outlook as the day progresses. Keep your eyes to the ranges around Melbourne.
5	Andrew McDonald	This ridge of high pressure will remain the dominant influence on our weather for almost the next week. I expect the high to eventually be pushed out of action by next Wednesday. Thursday or Friday next week currently looks to have a stronger cold front and accompanying cold pool behind it which could make things a little more interesting in terms of cold outbreaks. ATM this looks to be no May 15th 1999 but could produce our first real cold outbreak with cold air Cb's and hail showers.
5	Nick Sykes	Looks like we are in for an Indian Summer. All the models agree that S.E Australia will be dominated by high pressure for the next week. GASP has a high (1030+) parked just to the east of Vic early next week. Expect cool nights the next few as light winds and clear skies dominate. GASP, MRF, EC and NGP seem to indicate there could be some sort of upper trough around Monday next week, but looks weak.
4	Andrew McDonald	I should've picked the low forming in the strong cold pool. Still - BoM seem to think it will move E to ENE across N Vic. ATM is is moving just slightly S of due E which would land it on Melbourne. Adelaide has had reports of strong winds and branches/trees down. SW and Central Vic has the possibility of storms overnight and early tomorrow morning. CAPE is about 400-500 in the SW and W at 10pm tonight and LI's of -3 to -4. AVN has the cold pool moving to the N of Melbourne but if it keeps its current heading we could see LI's getting down to about -2 to -3 here overnight. Even if it does move ENE we are still expected to get LI's down to about -1. The cold pool on the W side of the low is still quite strong and could produce some nice cold air Cb's tomorrow morning too with a very steep lapse rate from the surface to the tropopause. These were Mt Gambier's obs at 10am this morning... 850mb +9C 700mb +2C 500mb -15C 300mb -45C 275mb -50C These are the sort of temps moving across Victoria overnight tonight so its not surprising that the BoM have included the chance of storms overnight. Chance of storms overnight in the SW of the state - 40%. Chance of storms in Melbourne overnight and early tomorrow morning 15-20%.
4	Chris Gribben	The current GMS sat pic (07.30z) is very interesting in my opinion. Shows the low has developed in Western Victoria but what is more interesting to me is the fact that despite it being deep to 300hpa, the cloud from what looks to be an upper disturbance appears to be streaming in from the NW over it. I am unsure at this stage whether this low over about Mt Gambier will drag this cloud band to the south. If it does I suspect rainfall amounts will increase considerably as the upper level cloud wraps around the low. If it doesn't affect the cloud band then I concur with Clyve on the rainfall amounts and comments he made re this system. It is certainly a fascinating sat pic at the moment
4	Clyve Herbert	Expected cyclogenesis (refer March 30 forecast) which has taken place over SW Victoria, should move east overnight and tomorrow. System should produce moderate to good rainfall over western & central districts. Reasonably cold air at 300hPa. Risks: developing low moving towards the Tasman Sea may become an East Coast Low situation with moderate to heavy falls, possibly south of Sydney to Gippsland. Potential: possible stream flooding from Wollongong south to the Victorian border. Outlook for the remainder of the week: Large High south of WA should ridge towards Tasmania, with a new high budding off to move across on Thursday / Friday. Cut off low in the Tasman Sea should be slow moving.
4	Andrew McDonald	SHORT TERM OUTLOOK This rain band might eventually reach here sometime mid morning (ie about 7-8am ish) but I don't think we'll see much in terms of significant rainfall totals. I'd be expecting no more than 5mm in southern areas and less in the N half of the state (if any). It is the cold pool behind the front through that has me a little interested. The latest IR sat pic run showed this cold pool growing fairly quickly and, from what I could see, it looked to be heading due W which would land the middle of it over Melbourne. I don't think this will happen though. Firstly, I'd expect it to get caught up in the WNW Jet forcing it slightly SSE over Tassie and then once in the Tasman it will get rocketed northwards as the upper level low and surface low both intensify with stronger southerly flow around the bottom of the lows. It still could make things a little more interesting early Wednesday with some nice cold air Cb's already popping up in that cold pool and on the SW edge of the low pressure system which is currently sitting off Adelaide. AVN has forecast 850mb temperatures to get down to between +1 and +3 which should make things a bit interesting. Freezing level in that case would be down to about 5000ft and hail showers could be a possibility during the early morning on Wednesday with the cooler overnight temperatures at the surface too. Thickness is supposedly getting down to about 547 (according to both GASP and AVN) which isn't too bad for this time of year. It'll be interesting to see what happens. I'd put the chances at about 25% for some cold air Cb's and about 20% for some Cb's tomorrow as the front moves through the E half of the state in the afternoon. EXTENDED OUTLOOK By Thursday this system will be all but gone as the next ridge of high pressure moves in to the state giving us some COLD starts in the mornings - I'll be expecting overnight temps on Thursday night of low single figures in the outer suburbs of Melbourne (ie +1 to +3C). This ridge will move slowly over Victoria giving us fine days and cool - cold nights until it moves out into the Tasman by later Saturday. Sunday should be warmer with a light - moderate N-NW'ly with cloud increasing in the W later as a front crosses the state, extending to the E by Monday with cooler SW'lys and showers in the rest of the state Monday.