Thunderstorms are one of the most beautiful atmospheric phenomenon and also are one of the most hazardous conditions that producesevere turbulence, low level windshear, low ceilings and visibilities, hail and lightning .
Thunderstorms are formed by a process called convection, defined as the transport of heat energy. Because the atmosphere is heated unevenly, an imbalance can occur which thunderstorms attempt to correct.Three things are needed for convection : moisture, lift and instability .
Moisture—Sufficient moisture must be present for clouds to form. Although convection occurs in the atmosphere without visible clouds, think thermalson a warm afternoon, moisture not only is the source of a visible cloud, butalso fuels the convection to continue
. As the warm air rises, it cools, and thewater vapor in the air condenses into cloud droplets. The condensation releases heat, allowing
the rising air to stay buoyant and continue to move upward.
Lift—There are many ways for air to be lifted in the atmosphere. Convection,or buoyancy, is one method. Other meteorological methodsinclude fronts,low pressure systems, interactions between thunderstorms, and interactions between the jet stream and the surfaceweather systems. Air also can be lifted by mechanical lift,such as when it is forced up and over a mountain range.Regardless
of how the air is lifted, if the lift is enough to make the air warmer than the surrounding air, convection can continue.
Instability—In general, as you increase in altitude, the air temperature cools up to the top of the troposphere. Of course, around fronts, mountains and in shallow layers near the ground, this is not always the case.How fast air cools is a measure of atmospheric stability . Meteorologists refer to this vertical change in temperature as the lapse rate.Outside of extremes, the temperature generally decreases from between 2.7oF - 5.4oF per 1000 feet. If the actual rising air cools slower than the lapse rate, the air remains relatively warm to compared the surroundings, and it continues to rise.
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Three stage of Thunderstorm
Cumulus stage : it's charecterized by countinous up drafts . in this stage a lifting action initiates the vertical movement of air .
as air rises and cools to it's dewpoint water vapor condenses into small water drroplets or ice crystals . if sufficient moisture is present the water vapor latent heat of condensation which released during condensation procers wil provides energy for the continued vertical growth of the cloud . Because of strong updrafts precipitation usually does not fall . instead the water drops or ice crystals rise and fall within the cloud and growing larger with each cycle also may creates hail . in cumulus stage of thunderstorm updrafts as fast as 3000 f.p.m may begin near the surface and extend well above the cloud top .
Mature stage : Thunderstorms reach the greatest intensity during the mature stage. as the drops in the cloud grow too large to be supported by the updrafts precipitation begins to falls to the surface . this creates a downward motion in the surrounding air and shows beginning of the mature stage . downdraft may reach velocity of 2500 f.p.m . the down-rushing air spreads outward at surface producing a sharp drop in temperature a rise in pressure , strong gusty wind and wind shear
conditions . (wind shear is a sudden drastic shift in wind speed and/or direction at vertical or horizental plane . ) as the thunderstorm advances a rolling , turbulent , circular-shaped cloud may form at the lower leading age of the cloud which called the rolling cloud .
Dissipating stage : unlike cumulus stage a dissipating thunderstorm is characterized by predominant down drafts . as the mature stage progresses more and more air aloft is disturbed by the falling drops . eventually the downdrafts begin to spread out within the cell taking the place of weakening updrafts . Because upward movement is necessary for condensation and release of the latent heat energy the entire thunderstorm begins to weaken . during this stage the upper level winds often blow the top of cloud downwind , creating the familiar anvil shape . how ever the anvile does not necessarily signal the storm's dissipation .
Types of tunderstorms
Tunderstorms usually have similar physical features but their intensity degree of development and associated weather to differ . thay are generally classified as Airmass and Frontal .
Air mass Thunderstorms
Air mass thunderstorms generally form in a warm , moist air and isolated or scattered over large area . they are usually caused by solar heating of the land which results in convection currents that lift unstable air and are most common during summer afternoons or in coastal areas at night . Air mass thunderstorms can also be caused by orographic lifting . although they are usually scattered along individual mountain peaks . they may cover large areas . they may be embedded in other clouds making them difficult to identify when approached from the Windward (the opposite of Lee ward ) side of a mountain . Nocturnal thunderstorms can occure in late spring and summer during the late night or early morning hours when relatively moist air exists aloft . they are usually found from the mississippi valley westward . nocturnal storms cover many square miles and their effects may continue for hours at a given location .
Frontal thunderstorms can be associated with any type of front . those which occure with a warm front are usually obscured by stratiform clouds . you should expect thunderstorms when there is showery precipitation near warm front . in a cold front the cumulonimbus clouds are often visible in a continuous line parallel to the frontal surface .
Note : Squall line is a narrow band of active thunderstorms which normally contains very severe weather and is often forms 50 to 300 miles ahead of front .