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18 10, 2017

Major Centres benefiting from Rain Deluge!

Issued 1pm Wednesday October 18th 2017. Over the past 5 days, most of the major cities, towns, metroplexes from Townsville to NENSW have been largely benefiting from this rain event, something that sometimes doesn’t happen.

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Its easy to forget when looking at all the high rainfall totals, both daily and accumulative across the rainfall event, that the majority of people living in Queensland are situated in major towns, cities and metropolitan regions. These same regions, are the regions who have missed on the few rain events going around since Cyclone Debbie back in March and while its far more beneficial for people outside of the cities to be getting the rainfall… at the end of the day if it doesn’t go through the populated areas, then to a large extent – people feel disappointed.

So how much has fallen over these regions? granted for those across the Capricornia, Central Coast and Tropical North Coast there is still another 24-48hrs of rainfall to come.

  • Maryborough 293.2mm:
    – 105mm (Tuesday) & 232.8mm (Mon to Wed) are the highest daily and 3 day totals since January 2013
    – Monthly total of 416.4mm: One of the highest October totals in history + wettest month since January 2013

  • Hervey Bay 278.8mm: 
    – 183.6mm (Mon / Tues): Highest 2 day total since January 2013
    – Monthly total of more than 400mm is a new RECORD

  • Bundaberg (AWS site) 278mm:
    – 224mm in the past 2 days
    – Monthly total of more than 500mm (RECORD) has shattered the old record of 280.6mm (set in 1953)
    – Highest monthly total since January 2013
    – First time 3 100mm days (October 3rd, 17th, 18th) since January 2013

    Bundaberg AWS topping over 100mm prior to 9am Wednesday, October 18th 2017 via Weatherzone

    Bundaberg AWS topping over 100mm prior to 9am Wednesday, October 18th 2017 via Weatherzone

     

  • Gympie 238.4mm:
    – 92.8mm on Tuesday: Highest daily total since February 2015
    – 4 days straight of 40mm+ for the first time since January 2013

  • Nambour (Sunshine Coast) 216.8mm:
    – Monthly total now at 314.4mm (2mm shy of the October record)

  • Maroochydore (Sunshine Coast) 188.2mm:
    – Monthly total now sitting at 295mm which is a new RECORD

  • Gladstone 127.6mm:
    – 102mm overnight is the highest daily total since Cyclone Debbie

  • Rockhampton 118.8mm:
    – 102mm overnight is the highest daily total since July 2016

  • Brisbane CBD 69.2mm:
    – 52.2mm (Sun / Mon) is the highest 2 day total since Cyclone Debbie

  • Ipswich 58mm:
    – 40.8mm for Monday: Highest daily total since Cyclone Debbie

  • Coolangatta (Gold Coast) 56mm:
    – 54mm (Sun / Mon) is the highest daily & 2 day total since July

  • Townsville 41mm:
    – More rainfall in the past 3 days than the previous 149 days before that (May 20 to October 15 inclusive) combined

    Waterfalls coming down Mt Coolum on the Sunshine Coast yesterday (Tuesday, October 17th) via Mike Wykes

    Waterfalls coming down Mt Coolum on the Sunshine Coast yesterday (Tuesday, October 17th) via Mike Wykes

     

     

Now these are just the major cities under the rain deluge, granted places like Brisbane, Ipswich and the Gold Coast haven’t had the same impacts as areas across the Wide Bay and Capricornia, but in their own rights its been the best rain in a while. Highest totals have been noted (some very significant) outside of the major centres and we will post further about these!

Lenthalls Dam Spillway, Maryborough before and after via Robin Williams

Lenthalls Dam Spillway, Maryborough before and after via Robin Williams

 

17 10, 2017

Lan could be the Strongest Typhoon in 2017

Issued 4pm AEST, Tuesday October 17th 2017. Severe Tropical Storm Lan is forecast to become the strongest Typhoon of 2017 as it tracks towards Eastern Japan over the next week! Above image current satellite imagery via NOAA

Severe Topical Storm Lan is still rated weaker than a Typhoon as it sits East of the Philippines over the Southern Philippine Sea. Lan developed near the Island of Yap, and over the past few days has drifted slowly towards the West gradually strengthening. Over the next week 24hrs however, Lan is expected to veer more towards the North as it encounters a high pressure ridge over South-East Asia.

This veer towards the North is expected to push Lan into an extremely favourable environment according to all global modelling, which will allow for rapid intensification over open waters. Lan at this stage is likely to continue on a general Northerly path where it may near the Islands between Japan and Taiwan. During this track, Lan is likely to not only reach Typhoon strength, but Super Typhoon strength with the Joint Typhoon Warning Center forecasting a maximum sustained winds of 130kts (240km/h) and maximum wind gusts of 160kts (nearly 300km/h). Lan’s pressure may also drop into the low 900’s. This will comfortably make Lan the strongest Typhoon for Season 2017 in the Western Pacific!

Forecast JTWC Track for Lan, valid Tuesday afternoon AEST.

Forecast JTWC Track for Lan, valid Tuesday afternoon AEST.

 

Lan’s final track and potential landfall is unknown due to many variables and large margin’s of error, however global modelling is in agreement that the Northerly track will place Lan in the general vicinity of Japan on around Sunday (October 22) or Monday (October 23). Thankfully it appears at this stage that some slightly unfavourable conditions surrounding Japan may quickly weaken the system back to a lower graded Typhoon, however Lan is also expected to be a very large system with a huge range from the centre for its damaging wind gusts – this will mean the system may not need to make landfall for its effects to be felt.

Its important to know that the above text and forecast is based off current data and is subject to changes and alterations. We will continue to monitor this system as it develops over the next few days and issue any updates if required.

 

Forecast model prediction for Lan's track - valid as of Tuesday (AEST) afternoon.

Forecast model prediction for Lan’s track – valid as of Tuesday (AEST) afternoon.

 

17 10, 2017

Fog Formations in South-East QLD & What causes them

Fog is essentially cloud on the ground which reduces visibility to less than 1km and is often referred to as “pea soup”. There are several different types of fog, including radiation fog, advection fog, valley fog, upslope fog, sea fog and freezing fog. All types of fog are able to be visually seen once formed and all have one common effect which is to reduce visibility, in some cases down to less than 50 metres. Thick fog creates hazardous driving conditions and greatly affects other modes of transport such as aviation and boating. In this article we will look at the 4 most common types of fog which occur most frequently during the Autumn and Winter months in the South East Queensland region.

 

Radiation fog covers larger areas forming during the night and early morning when there are clear skies and calm winds. There has to also be high humidity and surface air temperature needs to cool to within 3ºc of the dew point. Ground surface heat which has built up during the day quickly cools after sunset with heat being released back into the atmosphere. As the earth cools the layer of air just above the surface also cools but it cools quicker than other air a bit higher up which causes the bottom layer of cool air to become trapped. The trapped air near the surface continues to cool nearing the dew point or 100% relative humidity then water vapour condenses into tiny water droplets and fog is formed. When sun rise occurs the trapped cool air and fog layer near the surface begins to warm causing a reversal in the process. Fog will tend to rise, lift and “burn off” as the surface air is warmed further, air temperatures in the lower atmosphere and surface are equalled out while the dew point seperates causing the fog to evaporate.

Radiation Fog

Radiation Fog

Radiation Fog photo credit James Chambers

Radiation Fog photo credit James Chambers

 

Valley fog is concentrated into smaller areas between hills and mountains during the night and early morning which can occur more frequently than radiation fog due to local environment assistance. The principles of valley fog formation remain the same as the radiation fog process however due to cold air being more dense than warm air it sinks down the surrounding slopes concentrating into low areas. This is known as cold air drainage which feeds in extra amounts of cold air from surrounding higher elevations down into the valley where there is less escape.

ValleyFog

Valley Fog

Valley Fog

Valley Fog

 


Upslope fog occurs on higher elevations and ranges at any time of day or night. This type of fog forms when warm moist winds (Easterlies in our case) are forced up the slope of a mountain. As the air mass rises higher up the slope, the air pressure lowers, the air expands, and it cools to reach its dew point causing condensation and fog formation. Upslope fog can be long lasting during daylight hours especially if there is cloud cover above to block the suns heating. Locations along the Great Dividing Ranges such as Toowoomba are most prone to these types of fog.

Upslope Fog

Upslope Fog

Upslope Fog and Valley Fog

Upslope Fog and Valley Fog

Lake fog also known as steam fog occurs over lakes, dams and rivers where the water temperature is much warmer than the air temperature. Water vapour rises from the warm water surface then once becoming mixed with, and rapidly cooled by surrounding air, it condenses into tiny water droplets forming fog. Light winds and a large temperature difference is required for the development of this type of fog which mostly occurs at night or the very early morning. Interesting to note that due to phsyics the fog will never be allowed to reach the water surface!

Lake Fog

Lake Fog

17 10, 2017

Can Hail occur at night?

Its a common conspiracy that hailstones or hailstorms cant occur at night. Why this conspiracy has come about is unsure, it could be from the lack of hailstones people see, who knows… But this will answer that question and explain a bit about it.

Hail hitting Inverell after dark in October 2017 via Ali Marree

Hail hitting Inverell after dark in October 2017 via Ali Marree

 

The short answer is yes. Hail does without a doubt occur at night. I myself have chased several hailstorms after dark in Australia, and countless ones in the States – where I have even been under tornado warned Supercells at 2am which were warned for tennis to softball size hail! So from my own personal account (Thomas) I can assure you, hail does occur at night. That along with the thousands upon thousands of images and videos sent into Higgins Storm Chasing each year showing hail at night.

Its a bit of a mystery as to why people believe it doesn’t happen, but there is some science which can support people’s beliefs to a degree, but also explain the hail production process.

Hail West of Coolgardie, Northern NSW via ABC News

Hail West of Coolgardie, Northern NSW via ABC News

 

 

Hail occurs as water droplets are suspended above the freezing line, within the thunderstorm’s updraft. As time progresses, these water droplets freeze and as time continues… the stones grow bigger and bigger until the updraft’s strength can no longer maintain the weight of the stone. Thats when they fall down to Earth. A key characteristic of a thunderstorms updraft though is heating.. heat and humidity are key ingredients in making thunderstorms, however once the sun drops below the horizon… that heating element soon becomes non-existent and thunderstorms require other means to replace that heating process. The less heat, the weaker the updraft strength and overall cloud height. The lower the clouds, the smaller the area is below freezing (0ºc) within the thunderstorms updraft. The smaller the area, the less hail potential there is. So to a degree, some people may be thinking along those lines and while there is some merit in that argument… Hail (and large hail for that matter) does still occur. The thing is, day and night really have nothing to do with hail… hail is solely reliant on the updraft strength of a thunderstorm and the freezing potential within that thunderstorm (or the energy within the frozen air) – as long as those attributes are occurring, then there is no reason hail cant occur, especially within severe thunderstorms.

Illustration of how hail forms via NOAA

Illustration of how hail forms via NOAA

 

 

16 10, 2017

What are Microbursts?

Microbursts and macrobursts are potentially one of the least understood threats that regularly occur through the Australian Thunderstorm Season. By definition, they are both the same, there are just some very minute characteristics which differ between the two. Microbursts are essentially the more common of the two. So what are they, how do they occur and what are their threats?

 

 

Microburst over Phoenix, Arizona in July 2016 via Jerry Ferguson

Microburst over Phoenix, Arizona in July 2016 via Jerry Ferguson

What are they?
Microbursts and macrobursts are very intense downdrafts that occur within severe thunderstorms and supercell thunderstorms. These downdrafts surge from the clouds, down to the surface where the winds then hit the surface and spread out in a 360º fashion. The ferocity of the wind likely exceeds the damaging threshold of 90km/h, and its a strong reason for many thunderstorms becoming severely warned despite their tame appearance. Essentially… while the winds may seem tame, the conditions are favourable for a microburst or macroburst to occur at any moment. Stronger microbursts and macrobursts can exceed 125km/h winds (destructive criteria) and can even mimic the damage caused by tornadoes.

 

 

There are different forms of microburst’s and macroburst’s bursts also. You can have dry ones, which are far more common through inland parts of Australia and wet ones, which are far more common closer to the Coast and where high levels of tropical moisture are present. Dry ones typically resemble pure wind while a burst of very intense, frequent lightning may also occur near the its taken place. Wet ones of course have the wind, but are also accompanied by very heavy, potentially torrential, bursts of rainfall which will likely cause localised flash flooding. With wet micro/macro bursts, the visual appearance can resemble a rain bomb dropping out of the sky. 

 

Credit: Peter Thompson who sent these photos into Higgins Storm Chasing in January 2015 of a wet microburst occurring 80km North-East of Roma

Credit: Peter Thompson who sent these photos into Higgins Storm Chasing in January 2015 of a wet microburst occurring 80km North-East of Roma

What are their threats and characteristics?
Microbursts:

  • Usually less than 4km in diameter (about the size of a typical suburb)

  • They last up to 15 minutes with maximum intensity lasting between 2 and 4 minutes

  • Winds of 90-125km/h are common and in stronger ones, winds may easily exceed 150km/h!

  • These winds can down trees and powerlines, unroof homes and push cars off the road / highway. Stronger ones may also cause further more significant damage to homes and buildings while being able to push large trucks off highways. 

Macrobursts:

  • Usually larger than 4km in diameter

  • They can last for more than 15 minutes, but typically are less than 15 minutes also, with peak intensity lasting up to 5 minutes

  • Winds of 125km/h+ are usually likely, with peak winds potentially reaching 215km/h!

  • Macobursts have the ability to cause significant widespread damage due to their (by nature) stronger and larger size. They have the ability to cause tornado-like damage with buildings suffering significant structural damage, powerlines and trees downed, cars and trucks potentially rolled or blown off highways. 

16 10, 2017

What is a Landspout?

The term landspout is only a fairly new terminology in the weather world after it was introduced in 1985. The definition of a landspout is a tornado that isn’t associated with a mesocyclone, so by definition… yes landspouts are tornadoes, they are part of the tornado family, however their mechanics are just slightly different in how they form.

 

Landspout near Lara, VIC via Dave Evans (May 2007)

Landspout near Lara, VIC via Dave Evans (May 2007)

 

Landspouts are typically weaker than tornadoes which are produced by supercells and are much harder to detect on doppler radar imagery as the mechanics don’t usually produce a hook-echo on radar, although a weak couplet can sometimes be detected – especially in stronger landspouts. Landspouts are usually as stated above, much weaker than your typical tornado with a rating of EF-2 or less on the Enhanced Fujita Scale although stronger landspouts may reach EF-3 strength. By definition of the EFS (Enhanced Fujita Scale) EF-2 strength is capable of bringing down large trees and unroofing homes and businesses or severely damaging less sturdier buildings such as caravans. 

Landspout observed near Brisbane Airport on March 17th 2017 via Matt Houston

Landspout observed near Brisbane Airport on March 17th 2017 via Matt Houston

 

A unique characteristic of landspouts is that they normally have a translucent tube and they are virtually identical to waterspouts with the only difference being one is over land and one is over water. Not all landspouts are visible, and it usually takes the inclusion of dust, dirt, loose items such as leaves and debris to make the tube become visible. Due to this, they can often be misinterpreted for dust devils however there is the difference that landspouts develop under unstable, showery or stormy conditions where as dust devils develop over more unstable and heat-oriented blue skies.

Landspouts aren’t exactly uncommon in Australia and many tornadoes can be often misinterpreted for landspouts as the differences from a visual perspective can be so minute.

Landspout tornado observed near Cummins, SA in March 2009 via the ABC

Landspout tornado observed near Cummins, SA in March 2009 via the ABC

 

16 10, 2017

What is a Rain Shadow?

Rain shadows are related to and caused by orographic lifting. The process causes the opposite effects of rainfall by orographic lifting, on the opposite side of the mountain rain and as a result, rain shadows are renowned for producing some of the driest climates on planet Earth. Luckily, Australia doesn’t experience harsh rain shadow and this is largely due to the way our Country is shaped, however we do still experience them and in more ways than one.

 

So what are rain shadows, how do they occur and how do they impact Australia?
A ‘rain shadow’ is the dry area on the leeward side (the side away from the wind) on a mountainous area. The orographic lift effect forces moisture up one side of the mountain, where it then cools and condenses on that same side. A rain shadow occurs when this takes place and the mountains whilst producing rainfall also block rainfall from occur on the other side and therefore the name “rain shadow” is adopted as the mountain is casting a shadow of dryness over one side of the mountain. The leeward side of the mountain can also be remarkably hot as the sea breeze becomes blocked and humidity levels plummet. 

Illustration of how a rain shadow works

Illustration of how a rain shadow works

 

 

Rain shadows are renowned globally for producing some of the driest areas on the planet, and while the list is far too long to describe every single one of them.. there are some highlights from the list which are remarkable.

  • The Himalayan Mountains contribute to arid conditions across Central Asia including the Gobi Desert in Mongolia

  • The Arakan Mountains in Myanmar create a phenomenal difference… 750mm of rain occurs annually across Central Myanmar, whereas on the Rakhine Coast (the opposite side of the Mountains) more than 5500mm of rain occurs annually

  • The Judaean Hills in the Middle East are responsible for the Judaean Desert, Dead Sea and the Western slopes of the Moab Mountains. 

  • The Atacama Desert in Chile is the driest non-polar desert on Earth due to the Andes Mountains blocking moisture

  • South-Western parts of Hispaniola, Cuba and Jamaica are in the rain shadow of the trade winds and can receive less as little as 400mm per year compared to the North-Western sides who see more than 2000mm per year and the Highlands who can see as much as 5000mm per year!

  • Death Valley, the worlds hottest location, is located behind the Pacific Coast Ranges and the Sierra Nevada Range. Its the driest place in North America. 

  • Yellowknife, the most populated city in North-Western Canada, is located in the rain shadow of the Ranges to the West

  • San Jose and adjacent cities are usually drier than the rest of the San Francisco Bay area due to the Santa Cruz Mountains 

  • The valley of the Vardar River and south from Skopje to Athens is in the rain shadow of the Prokletije and Pindus Mountains. On its windward side the Prokletije has the highest rainfall in Europe at around 5,000mm with small glaciers even at mean annual temperatures well above 0 °C, but the leeward side receives as little as 400mm.

  • Hawaii may see the biggest rain shadow of the lot, with an entire island in the rain shadow of another island. The island of Kauai records on average, 12,700mm of rain per year due to orographic lifting yet on the Leeward side of the East Maui Volcano, the Island of Kahoolawe is virtually desert. 

    The Tibetan Plateau is probably the best example of a rain shadow around the world

    The Tibetan Plateau is probably the best example of a rain shadow around the world

     

     

There are 4 known official rain shadows within Australia however they arent as significant as those above

  • The Central Midlands of Tasmania receives about 20% of the rainfall than areas West of the Ranges including Mount Read

  • Monaro is shielded by the Snowy Mountains in both VIC and NSW

  • The Western side of Port Phillip Bay in Victoria is shielded by the Otway Ranges. The area between Geelong and Werribee is the driest area in Victoria yet the Otway’s record on average 2000mm per year.

  • In Western Australia, the Great Southern regions are shielded by the Darling Range. Dwellingup records on average 1000mm per year, with Narrogin around 130km to the East of Dwellingup, seeing just 500mm per year. 

So whats the other way we experience them in Australia?
Rain shadows can also be evident through the snow version of them also. While not many areas receive snowfall in Australia, there are some that miss out due to Rain Shadows (or I guess snow shadows in this case). Snowfall occurs down to low levels in Southern Tasmania every year, however due to the way the systems move through, its common for Hobart and more importantly the Highlands of Hobart to miss out. These areas are usually much higher than the forecast snow levels, however Mt Wellington casts a shadow over the region. The same occurs in Canberra where the odd system may produce snow below Canberra’s elevation but the Brindabella Ranges to the West and Snowy Mountains to the South-West cast a shadow over the majority of the ACT and inevitably Canberra. 

Why this occurs is the same process where dry air becomes trapped over the leeward side of the Ranges, so while the temperatures are perfectly adequate for snow to occur not only in those areas, but much lower.. the moisture level is shocking and precipitation struggles let alone snowfall. 

Areas in Australia impacted by Rain Shadows via BOM

Areas in Australia impacted by Rain Shadows via BOM

 

16 10, 2017

What are Steering Winds?

When we talk about thunderstorms and rain events, a term which is commonly used is steering winds or steering strength. These are arguably some of the most vital winds for any given weather event – whether its rain, showers, thunderstorms, cold fronts, East Coast Low’s even heatwaves can be influenced not so much by “steering winds”, but the winds within that part of the atmosphere. 

Where are the steering winds?
Steering winds are the winds between roughly 850mb and 600mb in the atmosphere. The variation is based solely around what the clouds are doing as lower based clouds may be impacted by the winds more likely between 850mb and 700mb, while higher based clouds may be impacted more by the winds between 700mb and 600mb. The term “mb” stands for millibar and its a standard unit of measurement when looking at the atmosphere, while the actual value in feet or kilometres differs ever so slightly from place to place, the millibar value remains the same as a way of comparing. When looking at these heights, 850mb is roughly around the 5,000ft mark while 600mb is closer to the 14,000-15,000ft mark. Its highly unusual for clouds to be influenced that high in the atmosphere, but its not completely unheard of.

 

What are the steering winds?
The steering winds are the low to mid level winds in the atmosphere which dictate the direction of thunderstorms and rain-bearing cells. While all cloud patterns are steered, its these winds which are most vital to us as weather chasers and reporters, along with the general public as its these winds which can be the life and death of a thunderstorm day for YOU individually. 

On a good thunderstorm day, the steering winds will move at a reasonable pace, somewhere in the vicinity of 30-50km/h. At this kind of pace, thunderstorms should push through and last long enough that it isn’t a 5 second show. If the steering winds become slower than that, then thunderstorms will become slower moving and then other issues such as a capping inversion and heating hours come into play, and storms may not reach the Coast. If the steering winds go any faster, then for chasers it can be very hard to keep up with cells (especially when dealing with traffic and road networks) but the thunderstorms will also be very much a one hit wonder. Its not unheard of for steering winds to exceed 100km/h, even 125km/h. These are the kinds of winds that mean if you blink you’ll miss the storm. 

If the steering winds mix with turning with height, in other words the winds from the surface to 10,000ft, 15,000ft or even higher turn as the go up, then this is where stationary rain areas and stationary thunderstorms come into play. These are the kinds of localised cells which have the ability to produce flash flooding as the cells don’t move. 

 

What are the threats with steering winds?
The other thing to note with steering winds, is the stronger they are, the more likely the severe potential is as these are the most likely winds to be dragged down to the surface through microbursts and downdrafts. As these winds accelerate on a downward trajectory its very possible that damaging to even destructive winds may occur.

An example of rotation the steering winds which could cause stationary storms / rain areas, increasing the flash flooding potential. Image via BSCH for November 18th (AM) North of Goondiwindi

An example of rotation the steering winds which could cause stationary storms / rain areas, increasing the flash flooding potential. Image via BSCH for November 18th (AM) North of Goondiwindi

 

16 10, 2017

Explaining What an East Coast Low is

Australian East Coast Low’s are extratropical cyclones. East Coast Low’s (or ECL’s as their initials) are not known as cyclones because we (being the general public, weather presenters and reporters, or even official agencies) refer to cyclones as the warm cored systems that impact the Australian tropics. In retrospect however, those are technically called ‘tropical’ cyclones. East Coast Low’s typically develop outside of the tropical waters and off the East Coast of Australia. The number can fluctuate greatly from year to year, but there have been as little as 0 recorded in some  years and in 1978/79 there were 12 observed. Many of these arent too overly severe with minimal impacts either due to duration or intensity.. there is the occurrence every year or second year however that sparks interest as these systems have the ability to produce catastrophic damage.

 

View of the 2007 ECL on Satellite via BOM

View of the 2007 ECL on Satellite via BOM

 

Australian ECL’s, although varying in size, typically all contain one common characteristic… widespread heavy to very heavy continuous rainfall. These cold core cyclones develop anywhere outside of the tropics off the East Coast of Australia which is roughly between Gladstone and Mallacoota which is located near the NSW / VIC Border right on the South-East corner of Mainland Australia – any further South from here and you now have a Tasman Low which is once again a cyclone but formed under different circumstances to both tropical and ECL’s, and any further North and you have yourself a tropical cyclone. These systems are renowned for producing catastrophic damage not only along the NSW and Southern QLD Coastlines, but extensive damage through major populated areas such as Sydney, Newcastle, Wollongong and Brisbane. ECL’s have the ability to rapidly develop in a matter of hours, unlike other forms of cyclones which can take longer and are one of the biggest severe threats to NSW on an annual basis. These systems are most likely during the winter months when upper level support can play a role in speeding up the rotation and development of these systems, while the cooler climate can help influence them also (as they are cold cored systems). Its also quite common for several East Coast Low’s to occur within close proximity to each other as conditions remain favourable for continued development. 

 

Beachside properties on the brink of collapsing after an ECL in 2016 caused mass havoc off the NSW Central Coast. Image via Peter Rae

Beachside properties on the brink of collapsing after an ECL in 2016 caused mass havoc off the NSW Central Coast. Image via Peter Rae

 

Threats of East Coast Low’s?
East Coast Low’s pose both a wind and rain threat to Australian mainland. The rain is the most obvious threat and likely threat, due to the fact the system doesn’t need to be over land for dangerous rainfall intensity to occur. Onshore winds wrapping around the ECL can produce significant amounts of rainfall over localised areas in a matter of 24 hours leading to significant and catastrophic flooding. The winds can become brutal too, with gusts of 90-125km/h common and well in excess of 150km/h possible in the strongest ECL’s. The good thing about the winds is while the broad scale can be gusty, the strongest winds are typically isolated and much closer to the system – so if it remains well offshore, its not so bad. They can also produce hazardous, dangerous or even life threatening sea conditions – for both human life and vessel. Waves can capsize boats, the swell can cause dangerous beach erosion and the overall effects of the Coastal waters can be hazardous for swimmers and beach-goers. 

Waves crashing over a cliff near Sydney during an East Coast Low in June 2016. Image via Jacob Ze Zwart

Waves crashing over a cliff near Sydney during an East Coast Low in June 2016. Image via Jacob Ze Zwart

 

HISTORIC ECL’S?
There have been several historic East Coast Low’s across history, but here are some of the more significant ones.

  • August 20, 1857 – A sailing ship reportedly carrying 122 people on board was wrecked off Sydney, with 121 people confirmed dead.

  • June 1950: Sydney recorded its highest monthly rainfall total in history for any month due to a series of consecutive ECL’s impacting the region

  • August 5, 1986 – Greater Sydney saw more than 300mm in 24hrs from a dangerous ECL with Sydney Observatory recording a station all-time record of 327mm.

  • December 7 & 8, 1998 – 6 participants in the Sydney to Hobart yacht race were killed as treacherous conditions caused by a very rapidly developing ECL directly impacted the race.

  • June 2007 (arguably the most famous of them all). The Pasha Bulka ship was grounded off the Coast of Newcastle. 10 people died as a result of 5 ECL’s developing within a very short period of time and more than $1.4 billion in damages were reported.

  • October 14, 2014 – Winds of 161km/h were recorded off the NSW Coast as torrential rain from a dangerous East Coast Low hit Greater Sydney.

  • April 20-23, 2015 – At least 4 people were killed in the worst flooding to hit the Hunter since the 2007 ECL which grounded the Pasha Bulka. Torrential rainfall with more than 500mm in less than 48hrs caused historic flooding through the areas of Maitland and Dungog which isolated entire towns for days. 

  • April 28 to May 1st, 2015 – An East Coast Low produced a very dangerous slow moving thunderstorm over North Brisbane which produced more than 300mm of rain in 3 hours leading to historic and catastrophic flooding over areas such as Caboolture and tragically killed at least 5 people who were trapped in cars during peak hour traffic.

    Severe flooding through Dungog, NSW during the 2015 East Coast Low

    Severe flooding through Dungog, NSW during the 2015 East Coast Low

     

16 10, 2017

What are Wall Clouds?

Wall clouds are some of the most eye capturing parts of storm chasing, and are often the visual appearance that a thunderstorm (or likely Supercell if a wall cloud is present) is taking the next step to becoming even more dangerous. The wall cloud typically indicates where the area of strongest updraft is occurring and rarely producing any precipitation itself, but rotating wall clouds can be a clear cut indication of a rotating mesocyclone within the thunderstorm which can produce tornadoes, some of which may become strong and deadly.

 

Mechanics of a Supercell showing where a wall cloud is located

Mechanics of a Supercell showing where a wall cloud is located

 

Wall clouds are formed through a process called entrainment. This is when warm, moist inflow air, rises and converges. It overpowers the rain-cooled air which is normally associated with the downdraft of a thunderstorm. As the warm air entrains the cooler air, the temperature and dew points increase. As the air continues to rise, it becomes statured which then leads to a process of further cloud development occurring and sometimes this process leads to the wall cloud developing. The wall cloud will also develop at the base of a thunderstorm and may also develop through the formation of rising scud. Wall clouds never produce precipitation as they are in an area called a ‘rain-free base’. The wall cloud is a clear cut indicator that a thunderstorm has entered supercell mode as its the clear cut line between the updraft and downdraft. The separation of these 2 drafts is vital for supercell production as this separation causes the mesocyclone to develop and work in perfect harmony. As long as this process takes place, a thunderstorm will remain a supercell.. as soon as the downdraft and updraft become mixed, then the storm begins to weaken. 

Their structure is unique as they can be anything from minuscule in size (in the big picture) to absolutely mammoth (between 1km and 8km+). As stated above, they form in the warmer inflow region of the storm which is coinciding with the direction of the steering winds. In the Northern hemisphere, wall clouds typically form on the Southern / South-West regions of a supercell, however they normally form over the Northern or North-East regions of a supercell in the Southern hemisphere. 

 

Wall cloud captured by NZP Chasers

Wall cloud captured by NZP Chasers

 

Attached to many wall clouds can be what is known as a tail cloud, which is a ragged band of cloud extending from the wall cloud to the precipitation core. Another accessory is the flumen cloud which is commonly known as a beavers tail. This is formed by warm, humid inflow in a strong thunderstorm but can often be mistaken for a tornado. Despite the presence of a beavers tail normally being associated with tornadic risk, the cloud itself does not rotate. 

 

Tornadogenesis is most likely to occur when the wall cloud has a persistent and rapid rotation present. The wall cloud itself however typically precedes tornadogensis by roughly between 10-20 minutes, but depending on the atmospheric conditions present on the day, it can be as little as a few minutes or as much as an hour or more. Although rotating, strong, ominous wall clouds typically contain tornadoes (and strong tornadoes for that matter), its not the rotating wall cloud itself that produces the tornado. That process is left to the rear flank downdraft (RFD) which initiates the tornado production. In some cases, when tornado families are born (a supercell which produces several individual tornadoes), the wall cloud will often die and become reinvigorated, long enough so it can spawn another tornado and often if this process is occurring, it will occur while the current tornado is still active. This is known as cyclic tornadogenesis.

Image of a huge rotating wall cloud over Wyoming. Image credit: Colt Forney

Image of a huge rotating wall cloud over Wyoming. Image credit: Colt Forney