Thunderstorm Cell Variants?
- Supercell
- Multicell
- Single Cell
- Squall Line
Spectacular weather associated with thunderstorms?
- Heavy showers
- Hail
- Squalls
- Downbursts
- Windshear
- Lightning
- Tornadoes
Conditions Required for Thunderstorms
- Atmospheric instability
- High Humidity
- Trigger
Examples of triggers for thunderstorms?
- a cold front
- terrain (orographic ascent)
- heating (thermals)
- heating by advection
- convergence of air (trough)
Three stages in a thunderstorm’s life cycle
- Cumulus/Developing
- Mature
- Dissipating
Elements of Cumulus/Developing stage of thunderstorm life cycle.
- Strong up-draughts - 5000fpm +
- Temp within cloud > outside;
- Above freezing level supercooled water or ice
- Lasts 10-20 minutes
Elements of Mature stage of thunderstorm life cycle
- Near the tropopause the Environmental lapse rate decreases
- ‘Anvil’ top may appear
- Precipitation particles can no-longer be held by up-draughts
- Falling precipitation causes down draughts
- Downbursts may occur beneath the cloud
- Out-flowing cold air causes mini-cold front
- Roll-cloud may appear ahead of storm
Elements of Dissipating stage of thunderstorm life cycle
- Precipitation occurs throughout the cloud
- Heaviest precipitation at the start
- Lightning disappears
- Hail (GR) unlikely
- If widespread TS existed, Ns, As may exist after.
Total typical lifespan for a thunderstorm?
30-60 minutes
Explain hail.
Hailstones form in the upper portions of a thunderstorm when super-cooled water droplets freeze onto ice crystals, which then grow in size as they are held aloft by updraughts within the storm.
True of false. Most hail does not reach the ground.
True. It melts during descent and falls as rain.
Almost all ______________ contain hail.
Cumulonimbus.
When does hail fall?
Hail falls when it becomes too large to be supported by the storm’s updraught or when it moves outside the storm’s updraught area. Hailstones can grow to the size of an orange in a storm with strong updraughts.
Where could small hail be experienced?
Small hail could be experienced below or clear of the thunderstorm as it could be thrown out of the top of cumulonimbus cloud and carried along by strong winds, sometimes several miles.
Where does large hail typically fall?
Large hail needs strong updraughts to remain aloft and therefore falls near the cumulonimbus, usually from the base.
Thunderstorm descriptors.
ISOL Isolated - individual clouds
OCNL Occasional - well separated clouds
FREQ Frequent - little or no separation between clouds
EMBD Embedded - within other clouds or layers or concealed by haze
What is a down-burst?
A sudden down-rush of air accompanying precipitation (SH GR SN) from a mature CB
What is the difference between microbursts and macrobursts?
- Microbursts - area less than 4km
- Macrobursts - area greater than 4 km
What are some clues suggesting a downburst?
- Virga
- Lowering and/or bulbous cloud-base
- Dust rings on ground
- Dark rain shaft
- Mammatus
