Thunderstorms are formed by cumulonimbus clouds and are characterized by lightning and thunder. They develop when certain atmospheric conditions are met, such as unstable lapse rates and sufficient water vapor. Thunderstorms can be triggered by different mechanisms like surface heating, frontal lifting, orographic lifting, and convergence. There are different types of thunderstorms including single cell, multicell, and supercells. Thunderstorms pose various hazards to aviation like turbulence, icing, hail, wind shear, lightning, tornadoes, and microbursts. Pilots can detect and avoid thunderstorms using weather radar and visual sighting, and recommended distances of avoidance depend on aircraft altitude.

1. ThunderstormsThunderstorms
Thunderstorm is form of weather characterized by the presence of
lighting and its acoustic effect – thunder. The meteorologically-assigned
cloud type associated with the thunderstorm is the cumulonimbus.
Thunderstorms are usually accompanied
by strong winds, heavy rain, snow and
hail.
About 45,000 thunderstorms take place each day
The lightning from these storms strikes Earth about 100 times each
second.
At any given time, there are an estimated
2,000 thunderstorms in progress, mostly in
tropical and subtropical latitudes

2. Development of theDevelopment of the
thunderstormsthunderstorms
Lapse rate greater than saturated adiabatic lapse rate
extending well above the freezing level
Sufficient water vapor to form and maintain the cloud
A trigger action to produce the ascent of the air and
cloud formation
Necessary conditions

3. Trigger actions for thunderstorms
Orographic lifting
Frontal lifting
Lifting due to convergence
Surface heating - convection

4. Surface heating -Surface heating -
convectionconvection
 Difficult to forecast, especially location
 Mainly in the afternoon
 Intense heating over wide area

5. Orographic liftingOrographic lifting
WIND
Forced ascent of air by orography generates cumulus clouds
Cells are frequently obscured by layer clouds (dangerous for flying)

6. Frontal liftingFrontal lifting

7. Frontal type thunderstormsFrontal type thunderstorms
 Occur on a cold front or at occlusionOccur on a cold front or at occlusion
 Can be embedded in layer cloudCan be embedded in layer cloud
associated with the frontassociated with the front
 Can occur over land or sea and at any time ofCan occur over land or sea and at any time of
the daythe day
 Can be found in active troughs andCan be found in active troughs and
depressionsdepressions
 Often accompanied with a squall lineOften accompanied with a squall line

8. Lifting due to convergenceLifting due to convergence

9. Stability of the atmosphereStability of the atmosphere
 For convection atmosphere mustFor convection atmosphere must
be unstablebe unstable
Skew T diagram showing instability
in layer between 700 and 200 mb
Stability of the atmosphere depends
on environmental lapse rate

10. Types of thunderstormsTypes of thunderstorms
 Single cellSingle cell
 Multicell (multicell cluster)Multicell (multicell cluster)
 SupercellSupercell

11. Single cell thunderstormSingle cell thunderstorm
stagesstages
The meteorologically-assignedcloud type associated
with the thunderstorm is cumulonimbus
Most common; last for less than an hour; built-in self-destruct
mechanism; occur all year long, but mostly in summer; can produce
strong winds, lightning, hail, and microbursts; three stages of growth

13. SupercellsSupercells

14. Thunderstorm hazardsThunderstorm hazards
 TurbulenceTurbulence
 IcingIcing
 Rain and snow (water ingestion)Rain and snow (water ingestion)
 HailHail
 Down-drought / MicroburstDown-drought / Microburst
 Wind shearWind shear
 LightningLightning
 TornadoesTornadoes

15. TurbulenceTurbulence
 Severe turbulence may be experienced in andSevere turbulence may be experienced in and
around the cloudaround the cloud
 Severe turbulence can be found 15-30 milesSevere turbulence can be found 15-30 miles
down stream from a storm core (gust front)down stream from a storm core (gust front)
 In the cloud severe turbulence can be found at any level, theIn the cloud severe turbulence can be found at any level, the
strongest turbulence is near the top of the cloud (excess of 5000strongest turbulence is near the top of the cloud (excess of 5000
fpm)fpm)
 Dangerous particularly during take off andDangerous particularly during take off and
landinglanding

16. ICINGICING
 The rapid and strong up currents provideThe rapid and strong up currents provide
large and plentiful super cooled water dropslarge and plentiful super cooled water drops
 Clear icing is possible to -30 CClear icing is possible to -30 C
 Rime icing can occur on temperatures even belowRime icing can occur on temperatures even below
-40 C-40 C
 The worst region is between the freezing level andThe worst region is between the freezing level and
-20 C-20 C

17. Rain / water ingestionRain / water ingestion
 Large quantities of water can be present inLarge quantities of water can be present in
Cb down to temperatures as low as -30 CCb down to temperatures as low as -30 C
 Sudden ingestion of this water by a turbineSudden ingestion of this water by a turbine
engine can cause flame-out or damageengine can cause flame-out or damage
 High liquid waterHigh liquid water
content can affectcontent can affect
aircraft pressureaircraft pressure
instrumentsinstruments

18. HailHail
 Hail may fall from the overhang of a Cb anvil into clear air belowHail may fall from the overhang of a Cb anvil into clear air below
 Severe structural damage can result fromSevere structural damage can result from
hail encounterhail encounter
 The largest recorded hail – about 150 mm (6”) in diameterThe largest recorded hail – about 150 mm (6”) in diameter
 TheThe 3/4" size limit for hail is based on a study
of the "smallest size of hailstones that cause
significant damage at airplane speeds between
200 and 300 mph."

19. Down drought / gust frontDown drought / gust front
 Precipitation from thunderstorm is likely to bePrecipitation from thunderstorm is likely to be
accompanied by a marked down draughtaccompanied by a marked down draught
 GGust frontust front -- the leading edge of cool air rushingthe leading edge of cool air rushing
down and out from adown and out from a thunderstormthunderstorm

20. Microburst (downburst)Microburst (downburst)
MMicrobursticroburst is a very localized column of sinking air, producingis a very localized column of sinking air, producing
damaging divergent anddamaging divergent and straight-line windsstraight-line winds at the surfaceat the surface
Two types of microburst: Wet and dry microburst
Diameter of microburst: < 5 km

21. Wind shearWind shear
 Wind shear is a difference in wind speed and direction over a relatively
short distance in the atmosphere
Wind shear is considered to be severe if the horizontal velocity changes
at least 15 m/sec over distances of 1 to 4 km. In the vertical, wind speeds
change at rates greater than 500 ft/min.

22. LightningLightning
 Lightning can do considerable damage toLightning can do considerable damage to
radio equipmentradio equipment
 Aircraft is likeAircraft is like a Faraday cage, therefore ita Faraday cage, therefore it
cannot be harmed by the external electric shock.cannot be harmed by the external electric shock.
 Lightning itself indicates huge energy, therefore
it has dynamical effects as well which can shake
the plane heavily by hitting it.

23. Detecting lightningDetecting lightning
 LLightning detector is a device that detectsightning detector is a device that detects
lightning produced bylightning produced by thunderstorms. Therethunderstorms. There
are airborne instruments tooare airborne instruments too
 Near real time mapping of lightningNear real time mapping of lightning

24. TornadoTornado
 VViolent, rotating column of airiolent, rotating column of air underunder
Cumulonimbus cloudCumulonimbus cloud
 Most tornadoes have wind speeds betweenMost tornadoes have wind speeds between
40 mph (64 km/h) and 110 mph (177 km/h), are40 mph (64 km/h) and 110 mph (177 km/h), are
approximately 250 feet (75 m) across and travelapproximately 250 feet (75 m) across and travel
a few miles (several kilometers) beforea few miles (several kilometers) before
dissipatingdissipating
 The most extreme can attain wind speeds ofThe most extreme can attain wind speeds of
more than 300 mph (480 km/h), stretch more thanmore than 300 mph (480 km/h), stretch more than
a mile (1.6 km) across, and stay on the grounda mile (1.6 km) across, and stay on the ground
for dozens of miles (more than 100 km)for dozens of miles (more than 100 km)

25. Location and avoidance ofLocation and avoidance of
thunderstormsthunderstorms
 When flying by day, at fairly high flight levelsWhen flying by day, at fairly high flight levels
it should be possible to see and so avoid,it should be possible to see and so avoid,
the tops of isolated CBthe tops of isolated CB
 At medium levels, or where Cb are moreAt medium levels, or where Cb are more
frequent, thunderstorms may be hidden byfrequent, thunderstorms may be hidden by
other cloudsother clouds
 Airborne weather radar (AWR) andAirborne weather radar (AWR) and
stormscopestormscope

26. Weather RadarWeather Radar
 The simplest rule is not to fly into cloudThe simplest rule is not to fly into cloud
formations giving strong contours on theformations giving strong contours on the
radar screenradar screen
Different types of radar screens

27. Recommended distancesRecommended distances
from thunderstormsfrom thunderstorms
Aircraft altitudeAircraft altitude AvoidanceAvoidance
distancedistance
UsingUsing
airborneairborne
WeatherWeather
radarradar
0 – 25000 ft0 – 25000 ft 10 NM10 NM
25000-30000 ft25000-30000 ft 15 NM15 NM
Above 30000 ftAbove 30000 ft 20 NM20 NM
VisualVisual All altitudes 10 NMAll altitudes 10 NM