Category Archives: Tornado

Tornado, tornadoes in Australia and Tornado Alley

Types of Storms

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Types of Storms

There are four main types of storms that most storms can be categorised into:

Single Cell thunderstorms

Single cell thunderstorms are those thunderstorms that develop independent of other thunderstorms. They simply go through the development stage, the mature stage and then dissipate without creating other cells. They may develop over a mountain or isolated hill. Single cell thunderstorms are not recognised as being very severe but occasionally, some larger single cell thunderstorms may develop with varying types of severe weather.


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Multicell thunderstorms

Multicell thunderstorms are thunderstorms consisting of several cells adjacent to one another in the various stages of development.

In most cases, thunderstorms tend to develop in adjacent clusters called multicells. However, multicells tend to go through several stages of development that allow for a longer life span. As cumulus develop, the dominating cumulus begins to grow into large cumulus eventually to produced light precipitation. As this precipitation and corresponding downdraft descends, evaporative cooling (evaporation is a cooling process) causes the air to accelerate towards the ground and flow outwards. In certain conditions, the descending and out flowing air can act as a wedge as the colder out flowing air undercuts the warm moist air in the regions surrounding the main cell. This can have the effect of intensifying updrafts of surrounding cells. These cells grow into their mature stage and also send down precipitation and become the dominant cell. At the same time, the newer cell produces downdrafts that interrupt the updraft of the original cell. Consequently, the older cell will begin to dissipate. This process is so efficient that the storm can last for up to a few hours or more with a continuously changing structure.

Stages in multicell development

Because of the unusual structure of multicells, the developing and dissipating process causes the storm to have a motion veering slightly at an angle to each cells line of motion. In other words, if for example the cells are moving east, multicellular development on the northern side has the effect of veering the overall storm to the northeast. An observer located to the east of the original cell will notice the original cell dying and the newer cell with precipitation developing to the north. The main precipitation will miss the observer.

This peculiar motion of multicells has confused and still confuses many people such as farmers into thinking the storm has 'changed direction' or 'come back again'. This confusion is due to the newer cell developing in a region on the side or even towards the rear side of the storm. Rapid development at the rear can also make a multicell appear to move in the opposite direction. These storms represent the best examples of ever-changing systems.

Multicell thunderstorms can become severe and depends on how efficient the arrangements of the downdrafts and updrafts. All types of severe weather can be experienced from severe multicells including giant hail, severe winds and tornadoes.

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Squall line thunderstorms

Squall lines are systems of thunderstorms arranged in a line. This line can extend for several hundred kilometres. Squall lines are normally very severe and produce some of the strongest straight line winds. It can produce other forms of severe weather even weak tornadoes.

To a certain extent, a squall line resembles a long system of multicell thunderstorms. The development is occurring on one end and dissipation is occurring on the other. However, in between these ends, the storm is very similar with a large anvil extending well ahead of the main body. There are no separate cells as is the case for multicells. As it approaches, a shelf cloud is normally observed with an extensive precipitation cascade. An approaching squall line is very dark and very spectacular. As it approaches, an observer will notice the strong updraft flowing into the storm band. A brief lull in the wind will be replaced with a sudden blast or squall of wind from the storm in the opposite direction (the downdraft). Moderate to heavy precipitation occurs near the downdraft. The precipitation will gradually decrease. The rear section is usually less spectacular but consists of a back anvil.

Squall lines develop as a result of a line boundary where warm moist air is undercut by colder air. Consequently, the downdraft flows down just behind the updraft. This is the reason why the shelf cloud develops. The cold air flowing downward condenses some of the water vapour contained in the updraft.Shelf cloud  lightning 13th October 2014

Squall lines move mostly at right angles to the direction of the cloud band. There is no confusion as in the case of the multicell type. At times, they can move quite rapidly.


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Supercell thunderstorms


Supercell thunderstorms
are the largest and the most severe of all types of thunderstorms. In fact supercells are so large they show up on a satellite photograph in the shape of a tear drop. Other types of severe thunderstorms also show up on satellite but individual cells are more difficult to make out. Most of the large tornadoes and giant hail events are spawned by supercells. They are also known for producing very severe straight line winds. The reason why supercells are the most severe is because of their rotating structure. The updrafts spiral into the storm and are not interrupted by the downdrafts which descend from a separate region of the storm.

 

Features and behaviour of supercells

The supercell itself is mainly one large cell. Because of the powerful updraft, the anvil extends a long distance ahead of the main body of the storm. The side anvils in particular are very thick and crisp. Towards the rear of a supercell thunderstorm, a dome protrudes above the top. This is also a result of the powerful updraft shooting through the inversion. The rear section of the supercell consists of a flanking line: a line of cumulus cells decreasing in height away from the main cell.

Various sections of a supercell consist of the different types of precipitation. Medium sized hail exist near the gust front with large to giant sized hail in the central section. This is often known as the hail shaft. The region where the flanking line meets storm is where wall clouds and tornadoes normally develop. Not all supercells produce wall clouds or tornadoes. These only develop when conditions are ideal. Tornadoes and wall cloud development are discussed further in the section on tornadoes, water spouts, land spouts and dust devils.

Unlike other storms, once supercells develop they produce their own energy. They are often regarded as mesocyclones. They do not require cold fronts or other forms of uplift to maintain their updrafts. Because of this efficiency, they last and may produce severe weather for several hours.

There are several complex factors that influence severity of supercells. The main factors are the strength of the updrafts and the strength of the upper level wind speeds. Particularly severe supercells have strong upper level winds which, based on the structure of supercells, has the effect of strengthening downdrafts and updrafts of the supercell.

El Reno Supercell 31st May 2013 Revisited

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El Reno Supercell 31st May 2013 Revisited

Ok it's not hard to recognise this event - El Reno 2013. Just accidentally run the video and noticed a lightning bolt after someone reported from memory and the audio as well that there was a tornado at the time - ie the firs tornado from the El Reno event.
Anyone know where exactly it was. The lightning illuminates the base quite well . It seems there is a wall cloud in the region. Was the first tornado multi-vortex in nature and therefore not as clearly visible as a full condensation funnel?screenshot-from-2016-11-25-20-11-43 screenshot-from-2016-11-25-20-12-51 screenshot-from-2016-11-25-20-13-49 screenshot-from-2016-11-25-20-14-13

Significant weather event South Australia 28 – 30 September 2016

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Significant Weather Event hits southern Australia

During the period 28 to 30 September 2016, a significant weather event unfolded across southern Australia that resulted in numerous weather phenomena occurring including thunderstorms, hail events, possible tornadoes, heavy rain, wind and flooding.
adelaiderain

sarainfall1week

murray darling significant rainfall

Murray Darling significant rainfall

tasmaniarain

nswrivers28sep

 

Significant Weather Event hits southern Australia

During the period 28 to 30 September 2016, a significant weather event unfolded across southern Australia that resulted in numerous weather phenomena occurring including thunderstorms, hail events, possible tornadoes, heavy rain, wind and flooding.

South Australia was by far the worst hit state with thunderstorms causing significant and widespread power outages across most of the state. It appears that two tornadoes may have occurred although the location has not been identified.

Up to 22 electricity towers and three high voltage power lines were brought down and an inter connector to the Victoria power grid was shut down. A multiple loss of 275,000 volt power lines during significant storm activity is the cause of the widespread state wide power outages. Power was restored to most of the state Thursday morning.

Severe Storms and Heavy Rainfall

A significant thunderstorm passed over the town of Clare north of Adelaide that dropped 34.6 mm of rain with most of that falling between 3.45 pm and 4.30 pm on the afternoon of the 28 September. The storm dropped 18.6 mm of rain between 3.47 pm and 4 pm which is more than 1 mm per minute.

Storm damage occurred at Melrose in the Flinders Ranges, Blyth and Clare and the towns of Blyth and Cleve were affected by significant hailstorms.

Thunderstorms passing over the Adelaide Hills during Wednesday afternoon dropped 25 to 35 mm of rain. By 9 am 29/9/2016, rainfall totals across the Adelaide Hills ranged from 30 to 79 mm with the highest totals around Mt Lofty.

The town of Clare had 53.8 mm of rain till 9 am 29/9/2016 followed by a further 32.8 mm to 9 am 30/9/16 for a total of 86.6 mm.

Strong wind gusts also featured and a peak wind gust of 91 km/h was observed at the Snowtown weather station at 3 pm on the 29/9/16 and a gust to 89 km/h occurred at Port Augusta at 12 noon (29/9/16).

A small number of rivers or localities are in flood and major flooding is occurring at South Para Reservoir while moderate flooding is occurring at seaustraliaweatherHeaslip Road.

Flooding

The storms and rain has caused havoc in the Barossa Valley with flooding occurring in low lying areas

The weather system moved across much of New South Wales and Victoria but the dramatic events that occurred in portions of South Australia did not occur. Reasonable rainfall totals were observed across the highlands of North East Victoria and southern New South Wales but significant downpours did not occur. For the week ending 1/10/16, the whole of North East Victoria and Southern New South Wales had received between 50 mm and 100 mm of rain but this was spread across 7 days. This was enough to cause renewed rises in local rivers and streams and minor flood warnings exists for the Kiewa River.

There were renewed snowfalls across the higher peaks of south east Australia and the Mt Hotham weather station recorded a peak wind gust of 144 km/h. A weather station at Falls Creek registered peak wind gusts to 107 km/between 2.15 am and 3 am on the 29/9/2016. Such winds were limited to alpine regions only.

As the system passed over, a numbered of centres experienced peak wind gusts of 80 km/h or greater including Ballarat (Victoria) and Broken Hill (Western New South Wales).

Across the farming belt of of New South Wales, rainfall was not heavy but it was persistent. There was enough rain to aggravate a significant flooding situation on the Lachlan River. At the present time, a major flood peak is passing along the Lachlan River between Euabalong to the west and Forbes to the east. That is a separate event in itself but it is causing significant disruption to communities in affected areas as it slowly passes downstream. Further rainfall across the region only aggravates the flooding situation.

Much of Tasmania was impacted by moderate to heavy rain on Friday morning. For the week ending 1/10/2016, parts of north west Tasmania had received in excess of 200 mm of rain while 50 to 100 mm fell around Hobart.

The satellite photo of southern Australia from NASA Worldview (AQUA) with overlays acquired 1/10/16 is showing an interesting cloud feature swirling around the southern part of the country. The low was centred over north west Victoria. Tasmania is being affected by heavy rain while a surge of cold air and low cloud surges north into South Australia.

CREDITS

Bureau of Meteorology - (Data from various weather stations) acquired 1/10/16.
Bureau of Meteorology - “Water and the Land” for rainfall plots.
NASA WORLDVIEW - Satellite photo of southern Australia for the 29/9/2016.

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