Transcript Thunderstorms

Thunderstorms
Spring 2016
Kyle Imhoff
Atmospheric Stability
 A Matter of Stability
• bubbles of air vs. the atmospheric environment
• bubbles change temperature by either
– dry adiabatic lapse rate (9.8C/1km) (5.5F/1,000ft)
– moist adiabatic lapse rate (5C/1km) (3.5F/1,000ft)
• Environment lapse rate varies
– Stability - a measure of whether an air bubble
moves when prodded (heated or forced lift)
• unstable - moves and never returns
• stable - may move, but returns to same place
Atmospheric Stability
 Stable Air
Characteristics
– clear or stratiform
clouds
– generally light surface
winds
– smoke, haze, smog
accumulate
– Inversions are common
(morning fog)
 Unstable Air
Characteristics
– clear or cumuliform
clouds
– generally gusty winds
– lack of haze
– Thunderstorms can
develop if enough
moisture is available
Thunderstorms
 Thunderstorms always form in an unstable
air mass - and are associated with
Cumulonimbus Clouds (Cb)
 Most thunderstorms occur in the spring and
summer (with a maximum in frequency
around the solstice - June 22)
 The majority of thunderstorms occur
between 2-8pm due to daytime heating
Thunderstorm Evolution
 Initial Stage
– Cumulus to Mature
– Strongest Vertical
Motions (25 m/sec)
– Cloud grows from
15,000-35,000 ft
– Electrification occurs
– Downdraft starts
– Heaviest rain and hail
– Life span: 20 minutes
 Mature Stage
– Mature to Dissipating
– Weaker Vertical
Motions (5-10 m/sec)
– Cloud reaches
maximum height spreads out into Anvil
– Downdraft spreads far
– Lighter rain
– Less Electrification
Life Cycle of a Thunderstorm
Where Storms Form
 Formation Zones
– Differences in
Temperature and
Moisture
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Clear/Cloudy regions
Sea/Lake Breeze
Mountain vs Valley
Edge of Fog areas
Dry line - West U.S.
Large River Valley
T-storm Types
 Types of T-Storms
– Air mass, single cell
– Clusters
– Supercell (HP or LP)
– Squall Lines
– Derechoes
– Mesoscale Convective
Complexes (MCC’s)
Squall Line
Squall Line/Air Mass
Thunderstorms
Effects
 The Effects of
Thunderstorms:
– Gust Front
• Straight-line winds
– Derecho
• Microbursts
– Tornadoes
• Mini and Maxi
– Fujita Scale
– Flash Flooding
– Hail
• pea to softball sized
Severe Thunderstorms
 Four main ingredients:
– Instability
– Moisture
– Lifting Mechanism
– Wind speed changes direction/speed with
height (called wind shear)
Forecasting Thunderstorms
 Storm Prediction Center
– Issues watches,
outlooks, discussions
regarding potential
severe thunderstorms
and tornadoes
 NWS Forecast Offices
– Issue warnings on
severe thunderstorms
and tornadoes
Summary
 Thunderstorms come in many shapes and
sizes – all produced by convection
 Key ingredients are instability, moisture,
and a lifting mechanism
 Very difficult to predict timing and location
of thunderstorms
 Important due to their potential
socioeconomic impacts