Graphics, explanations and animation on how they form.  How lightning is created and things you can learn and apply yourself when looking at thunderstorms.


   (currently under construction)                 (graphics courtesy NOAA)

   
keep visiting it's continually under construction!

THE INGREDIENTS

(1)  Moisture.
                                            (2) Instability
                                         (3) A lifting mechanism.


MOISTURE

Clouds are made up of water droplets so the moisture has to come from somewhere.  The 'fuel' for storms is moisture,  It can come by way of oceans, lakes, vegetation, wind and by a sufficient moisture  level at a certain atmospheric level over land. The temperature of the ocean plays an important role as wind carries the moisture, but is not the single one ingredient required.  Air heated over land will rise quicker than say cooler temperatures elsewhere in the vicinity, so the formation of storms in that particular area will be more dominant.  Troughs, convergence lines and fronts also play an important role where temperatures differ on either side.

In a nutshell a cloud is basically formed by a rising bubble or parcel of air that is lifted up into the atmosphere where it condenses and cools with height.  Warm air rises obviously, but the higher it goes, the cooler it becomes due to the colder temperatures it encounters.  It does not have to travel thousands of kilometres upward to reach what is known as its saturation point or dew point. This is where this bubble of air reaches its condensation zone and forms into cloud.  (Although the other terms that are used - LCL, LFC which mean Lifted Condensation Level, Layer of Free Convection)



 Once it is carried higher up it reaches an equilibrium area whereby it can't go up any further and must fall downward, so you then see it as rain drops or in extreme cases, hail.  This travel of the bubble or air parcel through the atmosphere is called the lapse rate.  This is where this air parcel increases in height but also decreases in temperature every thousand feet as it does so.  Lapse rates indicate to chasers how fast and how cold the parcels are rising and shows the temperature environment the parcel is entering.  It is a good indicator of instability in the atmosphere.  





           

    


    
INSTABILITY
Air is considered unstable if it continues to rise when given a nudge upward (or continues to sink if given a nudge downward). An unstable air mass is characterized by warm moist air near the surface and cold dry air aloft. In these situations, if a bubble or parcel of air is forced upward it will continue to rise on its own. As it rises it cools and some of the water vapor will condense, forming the familiar tall cumulonimbus cloud that is the thunderstorm.

Characteristics of an unstable air mass with warm moist air near the surface with colder and drier air aloft. Air that is forced upward will continue to rise, and air that is forced downward will continue to sink. (graphic shows this above on the right hand side)





LIFE CYCLE OF A THUNDERSTORM

(1) Growth stage

                                         (2) Mature stage

                                      (3) Dissipating stage.

 


During the growth stage this is where the storm rises to great heights, often up to 40-60,000 feet or 12+km.  The storm is updraught or inflow dominant meaning the air within the storm is rising on its own and has a good inflow of warm, moist air and mixing within the storm is consistent.



The mature stage is where the storm is self-sufficient and only requires available fuel to sustain itself, (although supercells are a different kettle of fish!)  It has an updraught (inflow) and downdraught (outflow) area within the core and this is the most dangerous period of the storm's life where it can produce strong wind, hail, flash flooding or even tornadoes.



The dissipating or dying stages of a storm is where the outflow winds cut off the incoming warmer, moist air that feeds the storm.  The outflow 'cold pools' surrounding the storm thus choking or depriving the storm of what it requires.  The storm becomes outflow dominant as opposed to inflow dominant.  You can see this as the storm appears to look weak as the rain falls and does not seem to 'grow' or look 'tight' and with no visible regeneration.  Rain seen falling around the middle or top of the storm into it is a good sign.


Hail

Cross section images show how hail is formed.  Hail is rare in Darwin but there have been chases where I've encountered hail from pea size to nail head size.  It does not sound impressive but for the tropics it is!




(Text courtesy NOAA for images above and below.)

This rain-free region is produced by the updraft and is what suspends rain and hail aloft producing the strong radar echo. (right)

  1. The hail nucleus, buoyed by the updraft is carried aloft by the updraft and begins to grow in size as it collides with supercooler raindrops and other small pieces of hail.

  2. Sometimes the hailstone is blown out of the main updraft and begins to falls to the earth.

  3. If the updraft is strong enough it will move the hailstone back into the cloud where it once again collides with water and hail and grows. This process may be repeated several times.

  4. In all cases, when the hailstone can no longer be supported by the updraft it falls to the earth. The stronger the updraft, the larger the hailstones that can be produced by the thunderstorm.






Wind shear from the storm is caused by the outflow of wind as it cycles down the storm's core.  You may have heard of aircraft avoiding thunderstorms?  This is the main reason apart from the lightning. Whilst the outflow may be a certain speed at one level, it may be higher at another and you can have several areas of outflow from large storms.  Downward traveling wind and aircraft don't mix!  Gust fronts are the effect of this outflow wind and it's what you feel just before the rain comes.





There's different types of storms and these are explained on another page on the site, but just for interest here I've added some more info.

single or pulse storm




multicell type




The most common storm in Darwin is the single or pulse storm, meaning they have only one 'cell' to their makeup. These have one updraught and one downdraught, that's it.  The water droplets remain within the storm until they are no longer able to be kept buoyant by the rising updraught and the weight of them has them falling back into the storm's inflow turning what was a nice fuel source into a wet soup.  This is why they are short lived.  In Darwin they only survive for around 40 minutes on average - some more, some even less.

Multicell storms are often referred to as cluster storms.  This is where dissipating storms at the front are being replaced by maturing storms behind.  They are known as backbuilding storms or stair-step storms also. They are  very common in Darwin and excellent to chase


Squall line storms

Squall line storms can be regular and do surprise locals early in the morning as nighttime heating enables the lines of storms to collect together over a very large area and move into Darwin.  During the day they are visible as shelf clouds as the storm spreads out horizontally.  Strong winds and heavy rain usually accompany these lines and an abundant amount of lightning can be experienced also.  Squall lines in Darwin travel from as far as the Gulf of Carpentaria from our north-east hundreds and hundreds of miles away and take several hours to reach us.



Supercell storms

Supercell storms are not indicative to our Darwin climate or atmospheric conditions.  Although we can get them during cyclonic activity they are rare to extinct in our tropical region.  Some severe storms have the appearance of a supercell and may produce rare hail but in fact are nothing close to what a supercell is.  Supercells are categorized as rotating thunderstorms and with a distinct mesocyclone.  Supercells are self-sustaining monsters that require totally different conditions - and in fact create their own conditions once mature!  They can be what's known as cyclic whereby the regenerate at an alarming rate and have multiple inflow/outflow areas and an 'exhaust' to vent unwanted/unfavorable air from within itself.


(Supercell photo credited to Rob MacDonald, Manitoba, Canada)



Lightning

Lightning is the most observed phenomena we associate with thunderstorms.  Whilst we know what makes it happen, there is room for debate on several other aspects to it.  Each day somewhere on the planet over 2,000 strikes occur,  Pretty impressive when you think about it.  Lightning carries with it all the ingredients to either destroy vegetation or enhance soil properties simply because of its composition.  There are many types of lightning and I won't go into the details of what they are, but this portion of the page will show you how it happens.


  

A channel of negative charge, called a "stepped leader" will descend from the bottom of the storm toward the ground . It is invisible to the human eye, and shoots to the ground in a series of rapid steps, each occurring in less time than it takes to blink your eye. As the negative leader approaches the ground, positive charge collects in the ground and in objects on the ground.




This positive charge "reaches" out to the approaching negative charge with its own channel, called a "streamer" . When these channels connect, the resulting electrical transfer is what we see as lightning. After the initial lightning stroke, if enough charge is leftover, additional lightning strokes will use the same channel and will give the bolt its flickering appearance.


                           


 

Lightning....

  • Causes an average of 80 fatalities and 300 injuries each year.
  • Lightning occurs in all thunderstorms; each year lightning strikes the Earth 20 million times.
  • The energy from one lightning flash could light a 100-watt light bulb for more than 3 months.
  • Most lightning fatalities and injuries occur when people are caught outdoors in the summer months during the afternoon and evening.
  • Lightning can occur from cloud-to-cloud, within a cloud, cloud-to-ground, or cloud-to-air.
  • Many fires in around the world are started by lightning.
  • The air near a lightning strike is heated to 50,000°F--hotter than the surface of the sun!
  • The rapid heating and cooling of the air near the lightning channel causes a shock wave that results in thunder.

 



  The best way to remember how close lightning is to you is this rule!