Category Archives: General Weather

General weather covering all aspects of weather from snow frost to severe weather and discussions on weather related terminilogy

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.

Giant Hailstones hit Sydney 18th February 2017

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Giant Hailstones hit Sydney 18th December 2017

Giant Hailstones hit Sydney 18th February 2017

Giant Hailstones hit Sydney 18th December 2017

Giant Hailstones hit Sydney 18th December 2017

A ferocious storm known as a supercell hit northwest and northern Sydney with hailstones up to 8cm smashed vehicles and skylights. The storm developed explosively near Bilpin and split with the eastern storm rapidly intensifying and moving east across the northern part of the city.




Large hailstones 4cm in diameter were first report from Londonderry and also Penrith and Richmond reported larger hailstones. The storm intensified and reports came in from Rouse Hill and Box Hill of significant hailstones to the size of 5cm in diameter as the storm rapidly moved east. Hailstones of 7cm was also reported at Glenhaven. the storm persisted and moved towards the Northern suburbs smashing homes and vehicles with more giant hailstones being reported. Serious lightning strikes also disrupted power across the region. This was the most violent hailstorm to hit the Sydney region since December 2007 when part of the region were hit by similar sized hailstones in Blacktown.

A change had entered the region which normally can deter storms from forming due to the cooler air at the surface. But temperatures across western Sydney and ample moisture persisted throughout the afternoon as the sun was allowed to continue baking the region. As the change moved inland, surface convergence along the change near Bilpin was able to break the solid lid on convection and an isolated storm developed. To rapidly exploded as it tapped the energy from warm moist air across the Sydney basin. Being relatively isolated allowed it to intensify to produce giant hailstones supported of course by upper cooling. 

More storms developed across the Illawarra and also the Central Coast with destructive warnings persisting until most of the storms exited the region.
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See : 128km Radar Loop for Sydney (Terrey Hills), 22:00 17/02/2017 to 22:00 18/02/2017 UTC


http://www.theweatherchaser.com/radar-loop/IDR714-sydney-terrey-hills/2017-02-17-22/2017-02-18-22

See : 64km Radar Loop for Sydney (Terrey Hills), 03:00 18/02/2017 to 22:00 18/02/2017 UTC

See : 128km Radar Loop for Wollongong, 22:00 17/02/2017 to 22:00 18/02/2017 UTC

Kyogle to Beaudesert Supercell – Lightning hits tree

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lightning hits a tree

Supercell - Lightning hits tree

Lightning hits tree. This is a longer version of the 3rd December 2016 Kyogle to Beaudesert Supercell. It was requested to me to provide a full account of the supercell from NSW through to Queensland. So I have put together a more in depth account of the chase beginning from Kyogle and on to areas north of Kyogle. Finally a better edit of the intense phase in Queensland from over the border through to Rathdowney where giant hail was reported. Next a lightning fest on approach to Beaudesert.

lightning hits a tree

lightning hits a tree

lightning hit a tree near the road 10metres away and then another in the field (which was filmed)! Please enjoy in full screen, HD and sound turned up!

It was a spectacular storm in its large size and very active lightning observed as well as significant hailstones. The storm being slow moving allowed for the relatively rare opportunity to chase in New South Wales and southern Queensland.

Staccato lightning

Staccato lightning

bell shaped updraft supercell

bell shaped updraft supercell

Supercell with very large hail

Supercell with very large hail

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