Australian Severe Weather Forum

NSW 7th to 9th December 2007 ( Forecast )

I think it is time for some discussion about the weekend prospects. I for one are very keen. At this stage the Mudgee to Dunedoo corridor along the Black Stump way and onto the Golden Hwy looks good over the weekend, but as always this may change with the last forecast before hitting the road.

GFS has been rather up and down, but has been consistently holding onto Saturday and Sunday as days to watch.

It has been a long time since I have seen CAPE values consistently over 3000 for such a large area.

The only worry I have is that the CAPE values have been modeled on 21C dew points, that is NOT going happen until rain falls. I think the TWC model is much more realistic in regard to dewpoint being closer to 16C.

Anyway it will still be an interesting weekend, wind shear will be much better than it has been of late. I think surface winds may be better than models indicate so shear could be interesting.

Hi Michael,

I too am quite interested in this coming weekend.  So much so that I'm leaving Brisbane tomorrow evening and starting my trek south. 

I don't have too much to add apart from a comment about the DP's.  I'm a little skeptical about the 21C DP's but I think by Saturday we'll see well mixed DP's in the 18-19C range as far S as central NSW.  DP's over southern QLD today have held in the 17-19C range even in the more elvated regions of Oakey, Toowoomba and Warwick.  These DP's held throughout the day indicating they are quite well mixed (ie not drying out much during the peak heating period of the day).  Of interest was the DP at Dalby this afternoon.  At 1pm it was 30/19.  By 3pm, the temperature had dropped to 29C but the DP had increased to 21C.  This mixed out in the few hours after this but has been sitting in the 19-20C range since.   This is quite encouraging as this moist air will advect southwards over the next 36hrs.

Shear is another interesting factor on Saturday (and Sunday).  GFS is doing some strange things that we don't see much of here in Australia...a low level jet!!  Sure its *only* 20-25knts but that is pretty good from where I sit.  Not only do we have one, but it is from the N (as opposed to the usual NW).  Sitting over the top of this is a moderate mid level jet with 700mb and 500mb winds getting into the 30-35knt range and both of these are from the NW or WNW.  And then up to we have a very tidy 80-90knt jet nosing into the area of interest. 

Two concerns for me.  The first being the cap.  Forecast soundings are indicating it could be quite strong with convective temps currently needing to push up to 33-34C to get things kicking.  The other concern is cloud.  There is quite a bit of this over SA and up into the NT.  GFS picks this up with hefty 500mb RH's currently mirroring this cloud band.  During tomorrow, this moves rapidly eastwards and clears most of NSW by later tomorrow night.  However, GFS has another burst of mid level RH (ie cloud) pushing down into NSW on Saturday.  It looks a little strange (possibly an anomoly) however time will tell. 

If it was Friday night and these models were for tomorrow...I'd be heading a little further W than Michael and probably sit somewhere like Trangie or even Nyngan. 

I have no doubt we will all be refining our forecasts over the next 24hrs and although Michael and I have already gone into a bit of detail, I encourage others to post their thoughts on this system.  You may only be able to chase locally near where you live but if you think it is a chance of a storm or two, post your thoughts - nothing like some good discussion before a decent storm outbreak. 

Today ( Friday ) and CAPE values just west of Nowra are well.................as good as get on the plains. Of course Nowra is not the plains in other aspects, but if a 15-20 knot NE wind can get inland to say Marulan it could given the other atmosphere winds be very interesting. a weak SE change is an added interesting feature - especially if winds go NW earlier in the day and the moisiture went thin.

Concerns - there is an ugly, ugly cloud band.

Getting very excited about today.I somehow scammed the day off work,so i'll be chasing somewhere. Given the amount of shear, and instability on the ranges,I think everywhere should get storms today including the coast.So having said that im very tempted to stay put today given the amount of CAPE just west of us here in Nowra. This area has had a hopeless season with a lack of quality storms,hopefully things will change today. The tracker already picks up a very lightning active storm just west of Wagga Wagga heading straight for Albury. The ugly cloudband should arive early to mid afternoon, hopefully this doesent ruin things.

Looks like the first 2 customers today are heading to just south of Wollongong from WNW and Newcastle.

I don't need to ad much to the comments already made but I think today we should see storms joining into a squall line considering the reasonably linear nature of the winds aloft being generally westerly. And it allready looks like this is happening on radar atm. I'm keeping close to the Katoomba/Lithgow area as storms will push through Sydney with such strong shear.

I would predict though that there will be isolated cells pop up before the line around the Lithgow/Bathurst corridor which could well produce some 3-4cm hail.

Jeff.

Update: The line of storms currently west of Canberra are moving quite fast, probably around 80-100km/h so very hard to chase.

This afternoon's storm was unusual to say the least. I had been at Parramatta where it was gradually getting cloudier and feeling like rain, but with no big anvils or anything visible. Started hearing reports on the radio that the storm had just hit Campbelltown and it was bucketing down, and just beat it home.

Started with light rain and developed into a real downpour with high winds. It was like being in a hurricane almost. Add to that lots of lightning (mostly up in the cloud but some healthy CGs). At Rydalmere we managed 17mm in 15 minutes, the news report just on Channel 10 said Sydney got 20mm in 10 minutes. Looking at the radar it was moving at a healthy rate as well - probably just as well, if it had been slower the amount of rain and local flooding would have been worse.

Nice work Jeff - a few isolated cells did go up ahead of the line over the mountains. One of them is looking awfully nice on Newcastle Radar around Singleton at 1720EDT . Certainly looks supercellular with it's northwards movement compared to the rest of the cells moving east north east. Hoping some one is up there to get some footage.

Tomorrow is looking very interesting. I would like to see more speed in the lower levels as the turn is more than ample for Supercells around the Nyngan to Mudgee to Narrabri area. Could be an early start from Sydney with a lengthy drive ahead.

Unfortunately also the sad news that someone was killed by the storms that crossed Sydney this afternoon when a shop awning collapsed on him at Balgowlah with the weight of water, also bringing down a load of bricks. While we might enjoy the storms there is often a downside to them in property damage and at worst injury or death..

The great lightning shots we capture or supercells we see, might also be hurting someone else. That's not to say we shouldn't keep doing what we are doing, but maybe think twice with the comments about wishing for a good day of storms. Maybe temper that wish with "a good day of storms that don't hurt anybody"!

While there have been a number of large cells in other parts of the state today, here in Armidale we just got a quite-lightning-active storm. The conditions have been good for storms for a number of days now, but this evening's was the first storm we've had in a fair while. Yesterday the radar indicated a few storms between Armidale and Glen Innes, though I didn't get a chance to see them personally.
The storm this evening came from the SW; the centre passed over Tamworth, before the system weakened a little , and became more messy on the way to Armidale. The first picture is the radar image of the storm close to Armidale. There were lighting flashes every few seconds, though few seemed to be CGs. I did manage to get a few (slightly blurry) photos, which I have uploaded. When the storm passed over there was only a short period of heavy rain, and the whole system, at our place in the North of the city, only provided an additional 3 mm to the large total that is building for December and indeed the whole year. Looking at the radar, we only got the northern end of the elongated centre of heavy rain, though the Airport, south of us, only recorded 1.8 mm. The winds also got quite high with 83 km/h recorded at one point at Armidale airport.

Hi guys,

Not much to report really - I think overkill - lots of storms, not much competition and too much of an anvil. I did chase down near Camden with David Croan and Paul Graham who somehow got separated from me. With a phone call from Nick, I asked were their other storms developing after the squall line. He confirmed a cell near Cowara. So I gave chase trying to get over the mountains with the risk that it might collapse. That it did 30km still to go. Oh well gave it a try and then came back home - nice drive to near Bathurst:)

Here are a few pictures:

Storms approaching near Camden - my camera did not get wasted on it I can tell you:


Storm near Bathurst - perhaps the storm could have attained LP structure earlier - who knows - definitely breaking down by the time I got within view:)




Regards,

Jimmy Deguara

I have to say I was expecting a better looking squall line than what eventuated...oh well. Not overly fussed about tomorrow either with what I am seeing on the 6z run, particularly at 500mb. After a late night, I'll see how I feel, but at most Mudgee-Bathurst region.

Forecast 8th December 2007 and Report 7th December 2007

Good luck today everyone. For those who are fully commited to todays chase can you let me know how green it is now around Walgett! Probably going to be a really good day for you Shaun. I'm unimpressed with how much this event has been downgraded in the last 24hrs. Instability has moved further north and there is the risk of mid level cloud interfering with any low level flow.

My dark horse bet for today is Oberon-Bathurst-Lithgow. It has stayed south of potential cloudbands in every forcast and is still looking at decent instability with the added bonus of possibly lots of dry air aloft which combined with altitude gives a very reasonable chance of good hail, either in size or quantity.

Yesterday was a bummer in the end. I didn't venture into the Blue Mountains after all after seeing how much precip was falling ahead of the squall line. I was a bit out with the location of predicted isolated cells as they formed further east than Lithgow/Bathurst but the ones that did develop showed some nice albeit weak inflow charicteristics at times.

Here's hoping today is much better!

Jeff.

Hi all, just a few pictures of a lovely wake up at 130am or so this morning at home.Constant crispy thunder with lightning retina burnage at times, were fairly close! A vigourous line of storms swept through which i'm sure woke everyone up in Lismore.
 
 
 

Report 8th December 2007

Hi,

I decided to head to near Lithgow leaving here at 1pm. I was hoping that something could develop within the critical timing before upper level warming created havoc.

A storm did develop near Bathurst but rather than head near it I relocate from north of Lithgow to near Portland with a decent view of the base from here. The storm did approach and dumped some precipitation but weakened with more updrafts developing on the north end. I gave one last shot to get a better view given it was progressing slowly east. The last pulse showed some half decent structure and then with the dreaded warming signs about 5pm, I called it a day.

Some pictures:

North of Lithgow


East of Portland


North of Cullen Bullen


Regards,

Jimmy Deguara