General Weather - all topics not current severe weather.

[Jimmy Deguara]

The January 27 2010 and January 28 2010 storm events are events worthy of mention, further discussion and investigation given the rare radar echo structures observed - namely hook echos. Furthermore, the location, close to a major populated area Sydney makes it more significant. Although no evidence of tornadoes have been observed until this point (and probably won't be), the events still are of concern given any number of cells could have become tornadic.

The January 27 2010 Dryline Supercell Outbreak with hook echo radar signatures
 
Although I don't have time at this point to research archives of the datasets, the 27th January 2010 produced several storms in the morning in the vicinity of the Central Tablelands and Central West Plains. A few of the cells in particular near Oberon and Orange moved east into a moist and very unstable environment. With a deep moist layer advecting westwards, shear profiles in the region near the southern parts of the Central Tablelands bordering Lithgow Jenolan, and the western part of the Wollemi were favourable for supercells. These storms became surface based and exhibited hook echos.

The first storm denoted as Storm A develops and quickly became severe, changes direction and produces the first hook about 40km south of Jenolan. The time period that best matches this behaviour is as follows

Begins 03:18 27/01/2010 UTC

Ends  04:24 27/01/2010 UTC


The second storm named as Storm B develops produces its hook towards the end of the life cycle of Storm A

Begins 04:18 27/01/2010 UTC

Ends 04:36 27/01/2010 UTC

A third storm we will name Storm C develops a hook after 04:30 27/01/2010 UTC and last perhaps until about the 05:00 27/01/2010 UTC time frame. This is the classic supercell complete with wall cloud and precipitation RFD cascade I intercepted. The base was visually rotating and this one was comparitvely less impressive or long lasting in terms of radar signature!

Storm C


A fourth storm denoted Storm D develops to its immediate NNW and cramps Storm C perhaps limiting its supply of inflow and eventually they become embedded and join into a complex with another Storm E now south of Kandos. This complex eventually moved and perhaps develop an HP supercell structure heading north along the range towards Merriwa - perhaps tracking a boundary until 09:42 27/01/2010 UTC.


Base and possible wall cloud of Storm D


Storm E situated south of Kandos north east of my location



Both storms C and Storm D crossed the Lithgow - Mudgee road and dropped hail perhaps to at least golf balls (not measured) or larger based on stripped leaves observations!

The January 28 2010 Supercells with significant hook echo signatures

With ample moisture once again in place over the coastal regions near Sydney the Hunter and Southern and Central Tablelands, an upper trough of sorts or cooling depicted on the models provided the basis for the development of significant supercells in these regions (Michael please provide the afternoon soundings for Sydney on both days then delete this message).

After multiple non-severe storms developed and tracked across the area, the first supercell We will call Storm F became anchored in the moisture south of Katoomba and tracked left of the easterly steering flow consistent with supercell behaviour - intense echos, slower storm motion in this case. Unconfirmed reports of hailstones to the size of oranges were possibly reported near Springwood and hailstones to 2 inches reported in Winmallee and W of Medway.

A second storm named Storm G develops and moves left developing a hook echo by 06:06 28/01/2010 UTC passing directly over Colo Heights. Significant wind shear couplets are observed on doppler radar just prior to Colo Heights. According to Harald Richter, the storm exhibits a mesocyclonic eye at some point in the vicinity of Colo Heights indicating a singificant circulation.

Storm F continues through the Wollemi National Park and exits into the Hunter Valley region. 5cm hail was intercepted from another storm that moved from Putty the one we got to Branxton.


At 06:42 28/01/2010 UTC, a double hook echo is observed on radar and this coincides with the time of the video taken as Nick and I and the ABC crew pass through most likely the second hook echo looking into the periphery of the first hook. Time of the video is adjusted to 5:52pm AEDT.

hook echo base January 28 2010

Conclusion

There are at least 3 hook echos on the January 27 2010 outbreak of supercells. There are also at least 3 hook echos identified from the January 28 2010 event and in one case a double hook echo on the storm ner Colo Heights.  Hook echos are relatively rare signatures depicted on Autralian radar even in a 5 year return time frame. Who knows what the return period is for hook echos with such an event in Australian history. Moreso, what is the return period of a consecutive day event with multiple hook echo signatures experienced on both days.

I encourage your input and discussion. This is an advanced scientific and factual based discussion. Please do not input thoughts that are uneducated guess work. Please do point out observations out time and/or location specific observations that are backed up by reliable sources. If not enjoy the read. (Any poorly researched or unreliable posts will be removed from this particular discussion. Any questions, please start a separate thread in General Weather - no general questions regarding terminology please. If you are unsure, contact the moderators.)

Regards,

Jimmy Deguara

[John Allen]

Im going to weigh in here with a consideration of the Aerological profile. One problem with this analysis is sydney is unavailable for the events in question, hence im going to use Williamstown, and modify the 00UTC profile to obtain a more appropriate rendition. I should note that the Wagga Wagga sounding is probably not too bad of the environment when daily heat is added (10UTC this airmass was likely passing over) on the 27th. Note that ive used the quick calculation to dewpoint along with the 3pm temp and Rel humidity.

So here is the original sounding, with the previous days show in light colour and hodograph.

Note that the original sounding had around 1900 CAPE, and a convective inhibition (CIN) of 60 J/Kg, LI -5.18, and very much veering shear in the lower atmosphere. Shear strength was also good deep throughout the atmosphere.

So for the 27th: T = 26.9 Td = 22.3.


Suddenly we have a significantly more dangerous profile:
CAPE : 2925 J/kg
CIN : 16 J/kg
LI: -7.18C
LCL and LFC have lifted somewhat from the unmodified sounding, but this probably isnt factual given the modification.

Even not considering what actually happened on the day this is a very significant and dangerous condition for Australian thunderstorm. Purely based on this I would say certain that we have a highly unstable environment conducive to HP type supercells, with CAPE values well above the 95th percentile for Australian Severe Thunderstorm Environments (STEs) based on some research ive been doing. The shear available is deep and in the moderate strength category, suggesting a potential for supercells however with subsequent storms forming post split on the flanking line. The biggest point about the shear is the strength and veer in the lowest 1km, allowing the development of strong LLC and mesocyclone type structure. Freezing level is 643mb....with a significant dry slot, conducive to large hail development and supercooling, EL to 12km.

Day 2:

CAPE: 2004 J/kg CIN: 42 J/kg LI: -6.04 veering shear in the lower atmosphere. Not incredibly strong though, so maybe this increased during the day.

New sounding T: 27.9 Td: 23

CAPE: 4369 J/kg
CIN: 17 J/kg
LI: -10.22

So this environment is even more exceptional in terms of energy, shear is not sufficient to inhibit the development of additional storms, however low level shear means organisation of the mesocyclone, and depth shear is enough to produce HP supercells in a very unstable environment. FZL is lower on this day, suggesting a greater chance of giant hail events, this is also characterised by an EL height over 13km. In my current climatology a CAPE environment of this level is unprecedented for this area in 5 years.


Final comments on the observational data available:
While the soundings are not perfectly located relative to the formative environment it is clear that the atmosphere in this region was associated with well-capped instability in excess of the 95th and 99th percentile for localised severe thunderstorm environments of this part of Australia. This alone is enough to suggest the potential for an exceptional pair of days with the passage of the dryline.

In terms of shear, deep layer shear is probably not the most significant factor here, it is sufficient for supercells but not the primary reason for their formation. In fact it is probably part of the inhibiting factor for isolated incredibly strong tornadic thunderstorms. The shear is insufficient to provide regulation for the flanking line and outflow boundary developments, hence resulting in competing and complex storms for both days. In terms of lower level and 0-4km/0-1km shear however we have a very different environment, while the shear is not overly strong(which wouldve produced bow echoes in this environment), it is more than sufficient, and associated with significant directional shear within the lowest 4km. This was likely more than sufficient to result in the development of strong mesocyclones within the very intense updrafts produced by these STEs.

In terms of the actual event data, I may be able to provide a much improved sounding and convective variable summary given the latitude/longitude locations and time of the incipient events based on MesoLAPS operational/forecast data from which I can derive soundings. This would be placed on a 12.5km grid giving a better *proximity* sounding.

Jimmy, in terms of rotational direction and storm development, did we have a left rotational member dominant or a uniform splitting supercells? Would you say the storm E/D complex was a singular large supercell with in a MC cluster, or more of a bow-echo structure?

Have you spoken to Harald Richter regarding gaining multi-level profiling of these storms from the Doppler?

[Jimmy Deguara]

John,

That is a very detailed analysis of the events. Thanks for the inpout.

Jimmy, in terms of rotational direction and storm development, did we have a left rotational member dominant or a uniform splitting supercells? Would you say the storm E/D complex was a singular large supercell with in a MC cluster, or more of a bow-echo structure?

The first supercell Storm C I observed I cannot tell if it was a split but the well formed formation suggests it was the dominant if a split occurred.

What you may find interesting in terms of further discussion are the timelapse. The first one is obviously a left mover with clockwise rotation about the wall cloud and RFD precipitation cascade.

The second supercell I chased Storm D certainly showed signs of a wall cloud but timelapse from my perspective does not clearly show rotation in any direction. Was there undercutting? I will place this online in due course for further discussion.

I have the opinion that Storm E developed with a left mover structure with no splitting. It had a left flanking line with a large base. I cannot confirm rotation or supercell status with this event but the initial phase of develop of the updraft from a cumulus stage showed clear signs that the storm was already willing to rotate.

Another point I would like to add was that there possibly was a moisture gradient north of these cells. The storm near Mudgee was definitely higher based even taking into account the drop of 500 metres in elevation. I couldd clearly see moisture being advected into the the cumulus stage development of Storm E.

Sadly, I did not continue to chase the complex of cells C D and E as I was hoping for an isolated cell that turned out to be the Mudgee event. Less competition - better chance of survival.

Regards,

Jimmy Deguara

[nmoir]

Though i doubt they will add much to the discussion here are 3 images from the 28th , the first being the supercell which went through Hazelbrook , you can see the beavertail . the 2nd and 3rd images are taken at the same time as jimmys video just north of Colo Heights under the base

[Michael Bath]

The radar loops from Terrey Hills radar can be accessed from the links below. Switch to broader scale or Doppler images as necessary.


128km Radar Loop for Sydney (Terrey Hills), 02:00 27/01/2010 to 08:00 27/01/2010 UTC



128km Radar Loop for Sydney (Terrey Hills), 00:00 28/01/2010 to 10:00 28/01/2010 UTC



Sydney Soundings. Afternoon sounding for the 27th is not available but you can see the previous trace on the morning of the 28th.

[John Allen]

Going to the radar imagery for the 27th first, (the important material, 0300-0700 UTC 27th Terry Hills 128km, 0300-0800 UTC 27th Terry Hills 256km.):

Cells: On preliminary analysis I would assess there to be a minimum of 10 Supercells during this event, possibly 3 more at later stages. Interestingly we have multiple SC modes and types:

1: Warragamba Dam Classic Left SC: Definite hook and left moving SC. This storm commenced around 3UTC, and collapsed on interaction with the Blackheath around 5UTC...but it wasn't the Blackheath storm that stopped this storm continuing, it exhibited extremely strong left moving supercellular structure and very intense returns with MC convection along its flanking line before what appears to be a new storm trying to form upwind collided with the Warragamba and Blackheath/Jenolan SCs as an outflow boundary. This storm underwent a split of a dying right moving component at around 3:30UTC. This storm had significant doppler returns in terms of a couplet.

2: Blackheath/Jenolan Classic left SC: The right mover from this storms split died very quickly, which meant that the Warragamba SC was uninterrupted, This storm was a pigeon pair to the first storm, with a strong hooked echo and left moving characteristics. It collapsed on interaction with the same storm which killed the Warragamba dam SC. 4:00UTC - 5:30UTC.

3: Portland Classic Left SC: This one is an interesting Left mover, in that unlike the other left movers of the day, its formation was associated with the formation of a significant right mover. The left mover had a very intense precip core, and strong hook echo, and became part of the latter enormous HP complex. 4:30UTC - 5:45UTC. This storm had significant doppler returns in terms of a couplet.

4: Portland Classic Right SC: This is one I didn't expect to see, it formed and had a significant core and hook echo, however, the bias of the shear environ appears to have resulted in this storm becoming part of a multicell line structure, which formed from the remnants of the Warragamba Dam/Blackheath SCs and this storm. It probably would have continued a bit longer had the atmosphere in the area not been so cluttered. 4:45UTC-5:45UTC

5&6, Left weak Classic, Left small HP:Prior to the complex forming there are two very distinct SC storms formed north of Portland. Storm 1 has a relatively weak precip core, however produces a hook echo near Kandos, storm two exhibits an almost flying eagle structure and hook echo to the east of this first storm. However these storms are relatively short lived as the Portland Left Mover arrives to form a very large rotating complex.

7: Kandos strong left HP SC: This was simply an enormous HP monster of a Supercell. It was formed by the collision of 5,6, and 3, and produced numerous hook echo structures on its NW flank, possibly being a cyclical producer of mesocyclones (see radar loop, the mesos generating the hooks form along the NW flank. This was probably the most dangerous storm of the day, and I believe was tapped into the maximum vertical energy out there. This storm persisted for some time with strong reflectivities, before interaction with the Mudgee cell and the passage of the outflow multicell which formed from the right mover overtook it. This storm exhibited the strongest meso-cyclone couplet of the day, and I would not be surprised if It produced tornadic activity. 

8: Camden left LP SC: This was a very small SC structure that persisted from around 600UTC to 700UTC. This storm then collapsed due to competition, however while formed it did produced a significant hook echo and TVS. Its quite possible that this was not a HP variety SC. It existed at the same time as the complex HP formed.

9: Mudgee ? SC: This is an unconfirmable, it was messy, but did look to have a hook signature for a short period of time. I tend to believe this weak structure was a result of not receiving the same energy available to the east, and possibly a not as favourable Lower shear environ.

10: Wellington ? SC: This one is also detectable on the 256km radar, and is best viewed around 0600UTC. This was a persistent and rotating storm with intense returns, however it did not produce a hook echo, probably for similar reasons to 9.

11&12: These were two random apparent right moving storms (possible SCs) in a flow which was to the NE. Both exhibited small but intense precip cores, and occurred in the latest part of the piece. Both are visible on the 256km radar imagery towards the end of the period near Kandos. The northern of the pair forms from a right split off a storm following the Wellington SC. The Southern forms of the edge of a storm near Cumnock.

13: This is an odd one, east of scone on the 256km we may have had a stationary SC on a TP. This storm is strong on return, however when it eventually splits the right mover is dominant...with the storms dying due to interaction soon after.

So not only do we have a very primed atmosphere for SCs, but a variety of SC modes occurring simultaneously.
3 Strong classic left moving SCs with hook echoes.
1 Strong Right moving SC split partner with hook echo.
1 Weaker classic left moving SC, with hook echo.
1 Strong HP type SC left mover, with hook echo.
1 Large complex HP SC, left moving and possibly cyclical with multiple hooks and possible TVS.
1 Possible left LP type SC with discernable hook.
1 Possible TP type SC with uniform split, not hooked.
2 Messy SC structures with left moving components not hooked.
2 Possible weak right moving SCs no hook.

Of the supercells produced, 8 have identifiable hook echoes at some stage of the their life cycle. It is quite possible that there were more than this. It appears the storms on the 27th of January formed in a strongly convective environment with moderate deep layer shear, and moderately strong low-level shear characterised by a SRH of 155. This resulted in a large number of classic supercells during the early part of formation, with HP becoming the more dominant mode at a later stage. Unusually, and probably a result of the relatively weak veer to the shear components, right moving supercells occurred at least once during the event. Further to the south, and likely on the dryline boundary in more marginal environments a LP type supercell with hook likely formed. Finally later in the event a number of less defined SCs formed of various types, suggesting there was enormous potential for this type of storm mode.

I will follow up with the 28th when I get a little time to do so.

[John Allen]

This space is reserved for analysis of the radar loop dated 28/1/2010.

Initial perusal suggests a large number of individual supercells prior to a pair of significant bow echo type events.

[nmoir]

I had a pretty long day searching along alot of fire trails and tracks near to the area where a tornado may have been but the only damage i saw was some leaf and twig stripping on a trail 4km north of mountain lagoon near Bilpin. having a look from the lookout there i could see no damage or tracks but this is very rugged and remote territory.

[Richary]

Being away in Vic last week missed the action, but that storm that formed near Mittagong on the 28th late in the loop (amybe 08 UT) looks quite interesting in the way it spread after the initial core formed. While I wasn't specifically looking for storm damage on the drive back up the Hume on Saturday didn't see anything unusual - and would have noticed had there been an unusual amount of debris on the side of the road.

[David C]

Just one other point to add to the above good discussion. Notwithstanding that storms on the 28th were wet classic to HP, another factor which makes these events all the more interesting, as far as potential for tornadoes, is the richness of the boundary layer moisture. This can be seen on the various soundings above. Very low dewpoint depressions are evident - all the chasers out and about will verify that the bases were particularly low on the 28th, and probably the 27th too. In addition, and equally important, the last Sydney sounding pasted up above also indicates a low LFC -- certainly no lower than 2000m and I'd suggest somewhere around 1000m in the pre-storm environment.

Jonathon Davies has some nice articles on the relationship between these two parameters to the extent that the relate to the development of tornadic supercells.



http://www.jondavies.net/LLthermo.PDF

[Jimmy Deguara]

Hi David and John,

John - interesting analysis of the 27th January supercell outbreak.

Very low dewpoint depressions are evident - all the chasers out and about will verify that the bases were particularly low on the 28th, and probably the 27th too.

Given the elevation, you would have anticipated that storm bases would almost be on the ground but they weren't. There were not as low in respect to being at about 1000 metres but they were sufficient to be of concern given real time rotation and timelapse of the storm. Had the storm not had competition from further north, this storm may have come close to producing. At no time did the storm show evidence of weakening or transformation into an HP supercell system for the 20 minutes or more of observing it. Such a tendency to form classic - HP supercell is an all too familiar scenario in Australia. The competition with the other cell to its immediate north also did not help in the strength and temperature of the inflow which could have enhanced low level rotation. The development of a sustained RFD is to me an encouragin sign for organisation although no RFD slot could be observed at any time either. An important component also to be considered given the dry line development is that cold air ourflow was not an issue.

Furthermore, I have unconfirmed reports from the region near Cullen Bullen (perhaps those working in the mines). Cars that were hit by this storm may have had hail dents similar to the Blacktown supercell that occurred on 9th December 2007. So estmiates of hail size would be in the range of 6 to 8cm although no known actual measurements as yet (just this observation and also the leaf litter). This supports John's analysis of a very intense core.

Regards,

Jimmy Deguara

[Michael T]

Certainly an interesting event. Great analysis, makes for good reading. What strikes me, as David mentioned, is the quality of low level moisture. Rarely in Australia do we see discrete storms firing with such low LCL's. The 9th of December Blacktown supercell formed in a higher CAPE environment but the LCL was significantly higher from memory (temp/dp approx. 32/21??).