Thunderstorms

[Ref #Understanding Weather & Climate, Books a la Carte Edition (6th Edition) ISBN-13: 978-0321773227 #Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 12-22]

What’s Thunder?

The tremendous increase in temperature during a lightning stroke causes the air expand explosively and produce the familiar sound of thunder;

Not all lightning produce sound – Heat lightning – lightning without thunder (have light no sound)

Notes:

  • Rule of thumb – count the number of seconds between the stroke and the thunder, then divide by three (or five), the result is the distance of thunder in kilometers (or miles) [Explanation – this is because of formula: “Speed = Distance/Time” and the speed of sound is 0.3 km/s (0.2 miles/s)]
    example:  lag between the flash and the sound is 3 s, then the thunder is around 1 km (0.6 miles) away
  • Also, nearby thunder – a loud, brief clap sound; short time lag between lightning and thunder
    (more distant – continuous rumble; long time lag even no thunder)

Two (2) main types of Thunderstorm

  1. Air mass thunderstorm
  2. Severe thunderstorm (Steady-state thunderstorms)

Notes: Tornadoes is actually a sort of thunderstorm!

 

Source: FAA-H-8083-25B Page 12-23

Basic 3 stages of a thunderstorm – developing, mature and dissipating

Developing stage, also known as ‘Cumulus stage”requires 3 factors –

  1. unstable air (instability),
  2. uplift (lifting processes) and
  3. water vapor (sufficient moisture)

The atmosphere becomes humid enough that newly formed clouds do not evaporate but instead undergo considerable vertical growth.

Continuous strong updrafts prohibit moisture from falling.

Developing stage lasts for approximately 15 minutes.

 

Mature stage is the most violent time period of the thunderstorm’s life cycle. Mature stage is acknowledged when when precipitation (heavy rain or hail) begins to fall, which create a downward motion of the air. Updrafts dominate the interior of the cloud, while Downdrafts occur inside as well as just outside it. The mature stage is the most violent time period of the thunderstorm’s life cycle – vilolent turbulence all exist within and near the cloud. The entrainment suppress further uplift. In a simply explanation, the top of the cloud spreads out and takes on an anvil-like shape. Then, the storm enters the dissipating stage.

Notes:

Entrainment

  • is the process that especially active along the edges of growing clouds
  • suppresses the growth of clouds by reduce the buoyant
    draw the ambient unsaturated air into the parcel at their margin, and thus causes some of the liquid droplets to evaporateconsumes latent heat and thereby cools the margin of the cloud

 

Dissipating stage is the time when the top of the cloud spreads out on an anvil-like shape – the appears washed-out – glaciated areas consist entirely of ice crystals (no liquid droplets). In addition, precipitation start to diminish.

 

Air mass thunderstorm

  • Least destructive
  • very localizedwithin uniform air masses (not occupy the entire air masses)
  • 3 Stages – developing, mature, dissipating

Severe thunderstorm/ Steady-state thunderstorms

  • Over a large area
  • Require wind shear for the formation
  • Mesoscale Convective Systems (MCSs) = Multi-cell thunderstorms – may have several clusters;
    Multi-cell thunderstorms have lifespans from 12hrs and even up to several days

    1. Squall lineslinear bands
    2. Mesoscale Convective Complexes (MCCs) – oval or roughly circular clusters
  • Supercells – intensely powerful storms that has a single updraft zone

Air mass thunderstorm → MCSs (Squall lines/MCCs)  → Supercells

 

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