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Some lovely (but very fast moving) supercells in the Hunter Valley. |
I was down in Sydney for a week doing some work, I may have had to work Friday – but was told on Thursday that I wasn’t required the following day, so I was able to chase! It was certainly looking good – a strong upper level cold pool moving north, with moist northerlies at the surface being dragged down to intersect. Shear was nothing short of awesome – and the system was extremely dynamic! The only problem was where to chase? My original thoughts lay to chase Sydney – but everyone told me I couldn’t chase there, it was impossible to do so with the roads. “Right, then, I’ll go south then.” To then get told I can’t chase either! So then I said “How about the Blue Mountains region?” “Nope.” Ok then…the Hunter? “Oh yeah, the Hunter is good to chase in!” (Well, I must say that my impression of chasing territory is somewhat to be desired given how disappointing the Hunter was to chase), but who needs great chasing area when you have absolutely mindblowing brilliant storms!?
I had organised to chase with a good friend of mine (Terry) – I wanted to catch up with him before I headed down to Melbourne the following day with Matt Pearce to attend the Monash Summer Weather School. I had to write a couple of reports in the morning for work – but once I did that I picked up Terry in Roseville from St Ives and then headed north on the freeway. We took the Cessnock exit as it’s quicker to go through Cessnock to get onto the New England Hwy than it is to go the way the signs tell you to. A storm had developed to our south – it looked nice, but there was also CJs to the NW of that which I thought might develop in a more pleasant area to chase in. A call from Doc (Matt Pearce) indicated the storm was strongly in the red – it didn’t look like it at that stage, but about ten minutes later it was taking on magnificent structure!!!
 
We jockeyed for position around the trees and discussed whether or not we’d make it if we headed back down the freeway. Some photos, footage and a quick bite of a sandwich and we headed back towards the freeway. The storm was moving SE – but from the angle I was watching it, I didn’t think it was going too far south, so thought we had a real chance! We headed south until the next exit, then headed west – we were getting HUGE drops on the windscreen from the RFB – quite an impressive one at that.
The anvil was spreading out overhead, but even as it spread out it was keeping a very cumuli appearance to it – I was quite impressed! Normally they tend to become quite wispy looking if they are blown by strong shear.
We headed near a town and then stopped for a bit to try and get some CGs on video – we got a few, but they occurred in between frames on the video! Soon the drops were getting massive – I was reciting to Terry how excited I was at the possibility of large hail! Sure enough, the first stones started falling – about one centimetre, but they didn’t get any bigger unfortunately! While it was hailing, Terry decided he had to go the toilet – “The toilet!? It’s hailing outside!” None the less, that didn’t stop Terry!!! Quite funny I thought (as per a few bellows of laughter on the video camera while videoing the hail). The storm appeared to be moving rapidly east, so we decided to head east too and get onto the freeway, and eventually head north. I got lost though and took the wrong turn, so it took about an extra five minutes to get onto the freeway.
One of the updraft bases was just starting to dump down as we got onto the freeway. The rain wasn’t heavy as such – but because we were driving so quickly into the massive drops it seemed heavier! As we emerged out of the rain it stopped suddenly – I glanced over to the east “OH MY GOD LOOK AT THE #@*(&@ WALL CLOUD!!!” There was a massive beast of a wall cloud hanging underneath to the main base! Only to have it go behind (what became a frequent frustration) trees!!!!!!!!!!!!!!!!!!!! I couldn’t get over how many trees lined the road. It was about five minutes until the next turnoff…still with trees.
The short glimpses I got of the wall cloud showed intense rotation – I could see the cloud moving faster than the car, while ragged bits of scud on the other side were FLYING the other way (combination of rapid motion & car forward speed). We did find a small clearing about 15 minutes later on a farmer’s property to which the wallcloud had weakened substantially, because the storm had gone out to sea.
 
We later found out that the original storm actually split, and we got the northern/left mover – but apparently the right mover looked even nicer – I would have loved to have seen that!!! All this and it wasn’t even 3pm yet. We tried to find a lookout to the ocean, but the storms were really moving rapidly – later to be confirmed up to 90-100km/h!!! No wonder we never had a chance of catching up properly once we got near the storm.
 
There was a bit of a lull again, we decided to head west and see if anything would develop. Things were looking…well, dead! Storms to the NE in the Mid North Coast were firing nicely, while storms (supercells) to the south were also firing.
Normally the Hunter fires later than the Sydney region, so it was a patience game. I got a call from Matt Smith who had just finished work at 4pm. He said he would come out and meet us – we met up for a late lunch at Cessnock. A line of stratocumuluogestus was to the west, but it was really struggling and was needing something else. Well, it looked like it was struggling anyway – that may not have been the case! Five minutes later when we came out of McDonalds, there was glaciation! And ten minutes later, there were BEAUTIFUL backshearing anvils, boiling and exploded updrafts, mammatus, knuckles – you name it!!! I was following Matt, and we could also see a shelf cloud to the west – talk about explosive development!!!
 
 
I had nearly given up on the thoughts of more storms for the day. We continued on to the southeast trying to get views and stopping periodically for photos – it was just amazing to watch!!!
 
We got into this treed area, and I thought I saw a funnel near the wallcloud region, but then it went back behind trees. Terry must have seen something, as going back through the video he had videoed part of it in the car! While looking at the sky, I saw Matt slam on his brakes…I wasn’t watching properly, so then slammed on my brakes and then pulled in front of him. He was pointing to the funnel (now weakening!)
 
But there was still strong rotation in a prong-like area just to the NW of the main wall cloud region!!
We decided to keep on going – the storm was flying! I half jokingly-half seriously said to Matt “Becareful that you don’t drive into a tornado!” But there ended up being no threat at that…somewhat windy roads and a storm moving at the same speed as you (if not faster) certainly doesn’t mix! And before we knew it, the storm had moved out to sea!
 
We pulled up near Swansea and wondered whether anything else could develop. We could see some storms about 40-50km to our northwest. We contemplated heading for them, but then decided to wait where we were as they’d probably move on top of us in about 20-30mins! Sure enough they did…we got some nice CGs (a good flang too!) and some heavy rain. But it was all over in a few minutes.
 
One last stratocumulogestus became lightning active, before it was clear blue sky to our west.
We found out that Jimmy was in the Hunter, so we decided to meet up with him, and saw a nice sunset on the way to Newcastle.
We went to the Newcastle Leagues Club to grab some dinner and have a chat about the recent events, before we went home – complimented by some nice lightning to the distant east heading back down to Sydney on the freeway!
I was surprised in Sydney when I had difficulty trying to get fuel – all of the service stations were shut!!! Normally most of them are open 24hrs in Brisbane, but I did get fuel (thankfully), before getting back home just after midnight, to try and head down to Melbourne later on that day…
Synoptic Overview
This was an extremely dynamic situation - I only wish I had more time to analyse it before I chased. I had just worked near 40hrs over the past three days, and had been averaging 4-5 hours sleep a night. I had been going out or doing things at night, and was getting up just after 5am the following day! So I was a little tired, but I was also doing forecasts for a company so I did have an idea on storm potential - just not a severe storm potential.
One of my concerns was how close the westerlies would encroach - the were a substantial low level westerly component, with only the far east part of the coast underneath a N to NE wind direction. I thought then that it would be no point heading west, very close to the upper trough and low as it would be offset by the drier air. As it was, very little developed to the west of the ranges - in fact, some storms didn't develop on the ranges (as they normally do), they formed to the east of the ranges on the day - testimony to the dry air that was pushing in from the west. The sky often looked relatively dry, and at one stage during the afternoon I was becoming doubtful of whether we would see another storm - but the upper dynamics were extreme, and that litterally made supercells out of Stratocumulogestus!!!
A look at the relative humidity analysis also shows that there was drier air encroaching into the Hunter region - however this may have only played a minor roll as there were other factors that ended up giving Sydney the best show on this day. However, the Hunter does generally require moisture to penetrate further west - and this is probably the reason why the NW Hunter did not produce many storms - had it done that, then things may have been once again much better for us! But the day was already great anyway!
There was an intense 500mb cold pool moving up from the south, it was throwing -15C @ 500mb over Sydney, and dropping down to -20 in the Central Tablelands - the Sydney morning sounding showed Sydney experiencing -20C @ 500mb overnight, certainly a lot of strength in it! It was -13 over the Hunter, but a strong isothermal gradient existed across most of the region - this helped in the strong shear and also added in the dynamics of the situation (ie, previously stable environments were becoming rapidly unstable due to the rapid cooling in the upper levels as the cold pool progressed over). There was also a strong low pressure region - a very large area was under 1000mb - somewhat unusual, often during this time of year (February) such a low pressure would be associated with a heat trough, and potentially dry NW'lies, but that was far from the case. The upper forcing was strengthening a surface low near the surface, sitting to the NE of the main cold pool. The strong surface low also aided in low level forcing to produce thunderstorms and also very quick development of convection.
The 300mb chart also showed good support of steep lapse rates throug the entire atmosphere with -41C @ 300mb, a very impressive 300mb temp! It quickly increased to around -38C in the Hunter region, in what was another tight isothermal gradient, ensuring good shear in the upper levels also. There was a slight upper ridge at 300mb to the west of the Central Tablelands - this is from the lowering of the tropopause with all of the cold air. A glance at the 200mb temps shows the upper warm air around 200mb very well from the tropopause (-45C @ 200mb, around 10-15C warmer than what it should be for that time of year, even -60C can be seen to the southeast of the Central NSW region out to sea).
The 850mb charts showed an interesting temperature increase - well, it wasn't so much interesting as it was frustrating to take into account. 850mb temps were expected to drop down to near 12 degrees around Sydney! This was awfully cold, and made me think that the trough may move through Sydney too early - in the end it didn't, but the other thing I was concerned about was the lack of a weaker cap. 16-17C @ 850mb was located over the Hunter region, this helped cap the Hunter a bit later - but the Hunter really wasn't the region to be on the day - Sydney was, and this interested me as I thought that the Hunter could really have been the place to be, even looking at shear...
850mb shear was 15-20 knots from the W, not bad - 700mb shear was pushing 35 knots from the NW, quite good really if you combine both of these. However it was upon closer analysis of the 500 and 300mb levels that helped explain why Sydney did a fair bit better than the Hunter on this day (not that the Hunter didn't fair badly with a total of 3 supercells!) The 500mb charts showed a diffluent jet 40-45 knots over the Sydney region, it was also 40-45 knots over the Hunter region, but it didn't show any diffluence. Effectively Sydney sat under the 500mb right exit region of the jet which was cradling the 500mb cold pool in the Central Tablelands. The compactness and the upper cold pool assisted in producing the jet over Sydney, in many situations such close proximity to the upper cold pool would often have a negative affect on shear strength - but that certainly was not the case in this setup.
The 300mb streamlines show an even more pronounced delta region over the Sydney region, with 70-80 WNW jet - over the Hunter it was stronger (80-90 knots), but the delta/right exit region sat to the south of the region, and there was less diffluence over the Hunter region. Once again, the compact size of the upper low appeared to have contributed to bringing the jet closer to the upper low, and thus into the area of steeper lapse rates and higher uplift. A look at the vertical velocities (at the bottom) also shows that on the day, the maximum uplift was predominantly over the Sydney region. The uplift came from the lifting effects of an upper level low (on the NE side), combining with the delta region and diffluent jet to help produce strong rising motion over the Sydney region. Updrafts were able to be stretched - most likely contributing to part of the vorticity and rotation, and the good shear (backing from the NNE to the W in the lower few kilometres at a considerable strength) combined to produce many supercells and storms that began to rotate very quickly, before they had even developed fully.
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