Yabba North & Katamatite Supercells

Andrew McDonald ("Macca")

18th December 2003

This day was an interesting day. The BoM had been forecasting storms in Melbourne for three or four days of this week and it excited a lot of Victorians with the possibility of that many storms in Melbourne in such a short period of time (our memories drifted back to November 30th - Dec 3rd 2003). High DP’s had plagued Victoria for the last few days and this day was no exception. On the morning of the 18th, a band of rain drifted across Victoria and cleared by around midday leaving very humid conditions in its wake. DP’s across the state were between 18C and 22C however cloud was keeping the temperatures down. A slow moving surface trough was sitting from Robinvale to King Island at around midday and at the same time an upper level trough was situated over the far SW of the state around Warrnambool to Naracoorte at the same time. The upper trough was relatively sharp, meaning that the upper levels were destabilising quite rapidly and the upper levels winds were generally from the NW from about 800mb (25knts) up to 400mb (50knts) with a W’ly jet above that getting up to 70-80knts. Below that, N to NE’ly winds were feeding into the trough at 15-25knts. I think the trough may’ve started to tilt positively and deepen somewhat during the day as it moved across Victoria, meaning the surface winds backed from N to NE during the day and strengthened!!!.

I was very fortunate this day in a way. I had to work and didn’t expect to be able to chase. My client was located in Carlton (just N of the CBD -  within walking distance of my office). I had been working there all morning listening to the rain (which stopped at about 11am) and wondering whether the forecast storms would occur behind the rainband or if the rainband was supposed to contain the storms. I figured the first option was a little more likely. I had to make my way back to the office during my lunch break to pick up some files for the afternoon (about a 40 min round trip) and I took my laptop with me so I could have a brief look at things from the office. On my walk back to the office, the cloud was breaking up and a few patches of sunshine were running around pushing the temperature up. The humidity was quite oppressive. A quick check of observations and the radar during my break showed a NICE line of storms forming to the NW of Melbourne moving towards the CBD!!! I thought I was in luck with the idea of copping a direct hit whilst at work. I grabbed my files and headed out the door on the 20 min walk back to the clients premises in Carlton thinking I had plenty of time to make it back before the storm hit.how wrong I was! - about half way into my walk it hit. Not overly heavy at first, but with about 5 mins to go, down it came. Torrential rain absolutely drenched me and my work bag, my suit and I were saturated. My manager took one look at me and suggested I head home and do the work from there (I ended up having to work late the next night to get it done). I wasn’t going to complain <g> so I jumped on a train and was home by about 3:45pm. It had rained for the entire journey home and my walk home from the station had nice rumbles of thunder every minute or so but it was now completely cloudy and I figured the day would be over. I took one look at radar and nearly crapped myself. A solid line of pink and red (40-100+mm/hr) storms were sitting from Pakenham to Castlemaine and a large isolated storm was sitting just N of the line near Bendigo. Fortunately I had all my chase gear in a backpack so I got changed into some dry clothes and grabbed by chase gear and was out the door in minutes.

The storms were only moving at about 35km/h and I figured a trip up the Hume Highway would allow me to overtake the line around Kilmore and then see what happened from there. I got caught in traffic on the Hume Highway at about 4:15pm but I eventually managed to get out onto the main part of the highway and into the heavy rain (which most people couldn’t drive in….). I punched through it just N of Kilmore and when I got a view to the W just after that I nearly died! A really nice flanking line, a BIG lowering (probably a wall cloud) and it was really really black behind me where I’d just driven. I grabbed some petrol and headed up to the Puckapunyal exit and turned off to the left to find a vantage point. It was now just after 5pm. The cell was JUST to my SW moving ENE and I found a quarry site which was fairly open so I stopped and grabbed some video and a picture (not worth showing) and the cell exhibited some weak rotation under the main updraft. The outflow blasted me pretty soon and the rain wasn’t too far behind it so I grabbed my gear and headed off (only noticing the "trespassers will be prosecuted" sign on the quarry gate as I left! hehe). I cruised E over the Hume Hwy towards Seymour and then took the turnoff to Mangalore, stopping briefly for some more video as the cell began to "line out" however it was still fairly impressive on the N end. The inflow on the N end was impressive into this cell and it was clear that it was going to keep going for a while however I received a call from David Simpson who told me there was a massive cell heading towards Shepparton. My brain immediately clicked ! this was the cell I had seen on radar from home that was near Bendigo.it was obviously still going and still going STRONG! I left immediately and headed N (bad move on my part to stay on the Mangalore road - I should’ve headed back to the Hume Hwy). I noted some minor flash flooding in Avenel as I made my way back to the Hume Hwy. My plan was to get to Euroa and then head NNW towards Shepparton, knowing that I’d have to drive through the storm at some stage.

I got to Euroa just before 6pm and managed to find my way through town to the Shepparton road (heading due NW for a while). As I drove, I noticed a nice looking cell with interesting structure off to my W. It was moving E and I was moving NW which meant that I got quite a bit closer to it over the next few minutes. In the end, I couldn’t resist so I stopped for a few pics and some brief video of the long flanking line base and a nice updraft region which soon exhibited wall cloud characteristics. Given the shear, I wasn’t surprised to see this structure but by this time I was close enough to the Shepparton action that I could hear loud BOOMS of thunder coming from further N.


I figured the cell further N would probably have uninterrupted inflow unlike this cell who’s inflow was somewhat killed by the bigger cell further N so I continued on. My road started heading due N (perfect!) into a dark precipitation area which was the back of the storm and I entered the precipitation at about 6:15pm and it got heavy rapidly. Very large drops of rain had me a bit worried about large hail on the N side of the storm but I only ended up hearing two or three loud thumps (sounded about 3cm) amongst the torrential rain. The rain rate probably peaked at about 120mm/hr or so and after about 10 minutes of driving through the rain I punched out the other side. I was greeted by a heavy green core to my E and what looked to be a line of outflow scud above me, and a nice developing base to my WSW. I worked out that I was just E of Shepparton (on the heavy vehicle route around Shepparton - a much quicker option than driving through Shepparton itself).

As I headed N around the E side of Shepparton, my view to the E got better and better and better. I soon realised that I was looking at a very large HP supercell with a very solid wall cloud and some amazing inflow. David Simpson informed me that both cells (the one to the E and the one to my WSW) were moving NE (woohooo!!! left movers!!!) and given that the cell was due E of me (probably over Pine Lodge) I had to get further N before I could head E. I took several pictures as I drove and also some AWESOME video to ensure I captured the structure of this beast. I managed to juggle the map, the camera and the steering wheel and picked out the road from Congupna to Katandra and Yabba North that would take me pretty close to this cell (it wasn’t far away - probably only 12km - but I wanted to be *really* close). The road headed ENE which was perfect. The cell was to my ESE and our paths were converging right on Yabba North!!! Luckily the 1-lane sealed road was quiet that afternoon as it enabled me to take more pics and video (nearly running off the road several times with excitement!!!!). The barrel shaped, striated wall cloud region was droolable!

As I got close to the cell between Katandra and Yabba North, the cell developed a cowcatcher inflow tail into the wall cloud!!! The inflow tail was about 100ft off the ground (literally) and it soon extended quite a way off to the NE. I was very excited by this stage and clear air CG’s started dropping out in front of the main updraft region.


I realised that my road was going to take me right under the wall cloud region and I was hoping to get a clear view of it before I got too close (I was only about 2km away now - hehe). To my dismay, a range of tiny hills (only about 50-80m high) blocked my view of the base!!! Normally this wouldn’t be a problem but as the base was soooo low, the hills prevented me from seeing it!!

Clear air CG’s were now hitting all around me fairly frequently. I was at the base of the hills on the W side and the wall cloud was JUST on the other side of the hills. I had the option of heading over the hills at Yabba North but I knew the road headed SE just on the other side (into the slightly dangerous part of the storm) so I had no option but to go N along the W side of the hills to see if I could get a view (this was VERY frustrating!!). I did get video of the cell as I was driving N and the video shows the wall cloud looking like something you would be much more likely to see on the plains of the US. This was the last gasp for this cell as it soon dropped a huge rain/hail core right in front of the main updraft and it became enveloped in rain (I literally didn’t look at it for 3 minutes and when I turned around, it was completely gone - hehe). I continued heading N to Youanmite and then E to the Benalla - Cobram road which headed NW to Katamatite.

David Simpson kept me updated as to where the cells were and I knew I could head W and intercept the cell I had seen earlier just WSW of Shepparton. As I headed NW, the cell appeared out of the haze to my SW. It looked somewhat linear as I approached it but you could clearly distinguish between the updraft region and the outflow. I stopped just SW of Katamatite for a short while and shot some video and took some photos. The cell showed signs of weak rotation but it was clear that the main updraft region was strengthening with scud being lifted rapidly from very low levels up into the updraft forming a nice wall cloud. A big downburst came down to the E of the main updraft, clearly separating the inflow and outflow regions of the cell. This seemed to be the telling factor as rotation increased somewhat and the cell seemed to intensify more.

I was forced to move NE back towards Katamatite to get out of the light precipitation which had started to fall out of the anvil. I moved about 3km NE and was now sitting about 5km W of Katamatite on the Katamatite-Numurkah road. I was able to stay here for quite a while watching the supercell intensify further. The wall cloud showed clear rotation and with the setting sun under the flanking line made for spectacular video and photos. I could’ve stayed here but a few spits of rain encouraged me to move about 2km further W to get a bit closer. This minor repositioning made for much better viewing and no rain.

Strongish (~20ktns) NE’lys were flowing into the storm, feeding in warm, moist air into the storm and the wall cloud intensified rapidly over the next 15 minutes and headed right for me. (At the time, Yarrawonga AWS (about 30km to my ENE) was reporting 26/22 with 15knt NE’lys gusting to 22knts). The most rapid rotation occurred almost directly overhead (yes I was, in hindsight, way too close!) and it was not long after I spotted it and videoed it for a brief time (I wasn’t going to not video it - hehe), I grabbed my camera gear and hotfooted it out of there.

After reviewing the video of this, I noted two small needle funnels which formed in parts of the wall cloud but nothing of significance.

A quick burst of speed to the E (back to my earlier position) had me in another nice viewing spot. The structure got more and more picturesque and as the sun set, the light got more and more impressive.


The cell was clearly maintaining its rotating structure however the base and wall cloud areas just got smaller in size I kept following the cell to Katamatite where I continued E (now on a dirt road). The striated base was lit up in shades of orange and then pink and with the foreground of freshly harvested hay bales it made for AWESOME photos and video.


Eventually the dirt road I was on became far too boggy and slippery to continue with the car fishtailing all over the road. One particular part of the road was completely covered in water for about 50m and I was rather concerned about getting bogged. I managed to find my way out of the maze of dirt roads in the region and back on to sealed roads and I started to make my way home. It was now about 9:15pm. I had been watching these supercells for about 3 hours and I was very content with what had been a phenomenal chase.


Several people called me during the afternoon telling me how big and impressive the cells were on radar and I was lucky enough to be in the right place at the right time to document the storms. Huge thanks to all those who updated me throughout the afternoon, especially David Simpson and Anthony Cornelius.

I spoke to the BoM the next day telling them what I had seen and they commented that the second storm in particular had a large BWER (Bound Weak Echo Region) on radar and a very nice supercell signature.

MSL - 4pm  

Radar Loop - big but worth it!!

Radar loop of the afternoon / evening

To further images from this day

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