Thunderstorms Flashcards
Req for Thunderstorm
Instability
Moisture
Lifting Force (Trigger like low p/frontal/surface heating)
Squall Line Thunderstorm
100 miles long
Often ahead of cold front
Building Stage Of Thunderstorm
- Updraughts
- Deep instability/moisture making cumulus cloud grow
- Wind speeds up to 60kts
Mature Phase
Last 20 minutes
Updraughts and downdraughts
Marked by precipitation
Dissipating phase
2 hours
Downdraughts only
Energy of downdraughts overcome energy of Updraughts
Lose energy and slow rain
Cloud base lifting due to evaporation
Gust Front
20km ahead of storm - 6000ft depth
Usually first indication of TS coming
Cooler air from down draft
Forces warm air to rise condense and develop roll clouds
Shelf cloud
Associated with gust front
Humid air rises from cold sinking air
Microburst
4km wide and do not last more than 5 minutes
Dry or wet (precipitation)
Macroburst
Last longer than 5 minutes and affects a larger area
Usually between 3-5 miles
Entire cold air outflow leaves TS
Microburst Hazards
1 - Headwind/airspeed rise
2 - Airspeed drops/high rate of descent
3 - Sudden tailwind/Lower airspeed
Virga
Rain that does not reach surface leading to downdraughts from cool sinking
Hail
High risk of ice conditions that can damage airframe
GR/GS
St Elmo’s fIRE
Visible discharge on windscreen and airframe at night
Super Cell Thunderstorm
Upper wind condition allow shifting of CB
No reduction in strength from downdrafts as falls in different area
Self propagating
Charge Distribution in Thunderstorm
Positive charged in upper cloud
Negative charge in lower cloud
Types of lightning
Intra Cloud
Cloud to Air
Cloud to ground
Cloud to cloud
Characters of tornado
Winds speeds can exceed 200kts
Referred to as funnel cloud if not touching ground
Referred to as water spout if over water
Ground speed is 20-40kts
Last up to 30 mins
150 in diameter
Dust devil
Rotating air caused by surface heating in hot dry calm conditions
10-100ft wide
Reach up to 650ft
Avoidance Info For Thunderstorms
Avoid by 10 miles up to 20,000ft
Avoid by 20 miles all sides and 5000ft vertically when above 20,000ft
Airborne Weather Radars Measure?
Detect rain droplets as well as hail/snow
Reflectivity of precipitation depends on diameter and water content of droplets
Blue/Green - Weak
Yellow/Orange - Moderate
Red - Strong
Lightning that shows from one cloud to another
Referred to as cloud-cloud
How if lightning formed
Result from electrical charge becoming strong enough to jump from cloud to the ground
Types of Thunderstorms
Air mass (heat thunderstorms) - no front/local/move slowly
Frontal - fast moving
Squall line thunderstorm - 100 miles long
Orographic thunderstorm
Thermal thunderstorm
Wind shear
Variation in wind velocity/direction over short distance
Virga can be a warning sign
Thermal Thunderstorm
ELR increases with surface heating
As surface heat though day instability builds
Likely during warm days with clear skies
Air Mass Thunderstorm
Warming of lower levels within air mass when cool air mass moves towards warmer surface
Steepens the lapse rate triggering thunderstorms
Near coasts in summer
Frontal Thunderstorms
Cold air mass undercuts a warm air mass.
Develop ahead of a colt front
Where is lightning most likely
Within 5000ft of freezing level
Temperature between +10 and -10
Strikes a sharp edges like wingtip or nose - becomes part of lightning trajectory
Where is hazardous hailstones reaching the ground most likely to be experienced below CBS?
Continental areas of mid latitude due to the freezing level being lower around 11,000ft
How many tornadoes typically occur in NA each year
More than 1000
Warning sign of wind shear is
Virga
