How to Recognize, Identify, and
Report Severe Weather

• Watch : conditions are favorable for severe weather
• Warning : severe weather is currently occurring in the area
• Watches and warnings are issued for: severe thunderstorms, hail, flash floods, and tornadoes

• Every Thunderstorm Needs:
– Moisture
– Unstable Air (warm air to rise rapidly)
– Lift (cold front)
• There are three stages in the life cycle of a thunderstorm
– Developing (Cumulus) stage
– Mature stage
– Dissipating stage

• Developing Stage
– Rising cumulus clouds; strong updraft
– Little if any precipitation
– Lasts about 10 minutes
– Occasional lightning

• Mature Stage
– Updraft and downdraft
– Most likely time for heavy rain, frequent lightning, strong winds, and hail
– Tornado development is possible
– Averages 10-20 minutes, but can last a few hours

• Dissipating Stage
– Weakened updraft
– Rainfall lessens in intensity
– Lightning and strong winds remain a threat

• Single Cell (Pulse) :
– Generally weak, short lived, and poorly organized
• Multicell Cluster :
– Most common type
– Series of cells moving as one unit
• Multicell Line :
– AKA “Squall Line”
– Long line of storms with gust front at leading edge
• Supercell :
– Very strong and produce severe weather

• A thunderstorm is classified as severe if it has any of the following characteristics
– Hail greater than 0.75” in diameter (dime size)
– Winds greater than 58 miles per hour
– Tornado

• 20-30 minutes
• Rarely turn severe
• Heavy rainfall and weak tornadoes are still possible
• Poorly organized

• Most common type of thunderstorm
• Each cell in the cluster is at a different stage of the thunderstorm life cycle
• Each cell may last 20 minutes, but each cluster can last several hours
• Heavy rain, downbursts, moderate sized hail, occasional weak tornadoes

• Squall Line
• Long line of storms with a continuous, well developed gust front at leading edge of the line
• Heaviest rain is at center of line
• Produce heavy rain, hail, and tornadoes
• Strong downbursts can cause line to bend and become a “bow echo”

• Rarest type of thunderstorm, but the most dangerous
• The updraft rotates (called mesocyclone)
• Large hail
• Heavy downpours
• Strong downbursts
• Strong to violent tornadoes

Supercell Thunderstorm (w/o Tornado)

Supercell Thunderstorm (w/Tornado)

Supercell Thunderstorm (w/Tornado)

• Flash Floods
• Lightning
• Hail
• Downbursts
• Tornadoes

• #1 cause of death associated with thunderstorms
• An average of 140 fatalities every year (in US)
• Definition: a rapid rise in water (creeks, streams, drainage ditches) within 12 hours of a period of heavy rain
– As little as 6 inches can knock a human over
– Two feet of water can move a car
– “Turn Around, Don’t Drown”
– Get to higher ground immediately

• Lightning occurs in all thunderstorms
• Causes an average of 80 fatalities and 300 injuries per year (in the US)
• Lightning strikes the tallest object
– If caught outside crouch down in a ball
• 30/30 Rule
– Go indoors if you hear thunder before counting to 30 after you see lightning
– Wait inside for 30 minutes after you last hear thunder

• Rarely causes fatalities, but causes significant damage to property and crops
• Can fall at rates up to
100 miles per hour
• Created by strong updrafts in thunderstorm

• Sizing Chart
– Pea
– Penny/Dime (Severe Criteria)
– Nickel
– Quarter
– Half Dollar
– Ping Pong Ball
– Golf ball
– Hen Egg
– Tennis Ball
– Baseball
– Grapefruit
– Softball
1.75”
2.00”
2.50”
2.75”
4.00”
4.50”
0.25”
0.75”
0.88”
1.00”
1.25”
1.50”

• A strong downdraft with an outrush of damaging winds at the surface
• Winds can reach 100 miles per hour or more
• Straight line winds
• Winds speed and direction can change rapidly

• Wind Speed Estimates (mph)
– 25-31: large branches in motion; whistling in telephone wires
– 32-38: whole trees in motion
– 39-54: twigs break off of trees; wind impedes walking
– 55-72: damage to chimneys and TV antennas; pushes over shallow rooted trees
– 73-112: peels surface off roofs; windows broken; trailer houses overturned
– 113+: roofs torn off houses; weak building destroyed; large trees uprooted

• Several cloud formations are associated with a thunderstorm that can be confused with an actual tornado
– Wall clouds
– Shelf clouds
– Roll clouds
• A roll cloud is similar to a shelf cloud, but it is detached from the main “parent cloud” whereas a shelf cloud is part of the main storm cloud
– Scud Clouds
• Detached and wind torn – similar shape to wall/funnel clouds

Wall Cloud Shelf Cloud
Suggest Inflow/Updraft
Suggest
Outflow/Downdraft
Maintain position with respect to rain
Move away from rain
Slope upward away from precipitation
Slope downward away from precipitation

• What is the tornado potential for a wall cloud?
– It will be consistent, lasting 10-20 minutes
– It will have persistent rotation
– Strong winds will blow into the wall cloud from the south or southeast (25-35 mph)
– It will exhibit evidence of rapid vertical motion
• These are rules of thumb – there are always exceptions!

• A tornado is a violently rotating column of air in contact with the ground extending from a thunderstorm
• May appear transparent until dirt and debris are picked up in the vortex or until a condensation cloud forms
• A tornado that forms over a body of water is called a waterspout

• Tornadoes can occur at any time, any day, and in any state
• They are most common
– In tornado alley: Texas north to Nebraska and east to Indiana
– During the spring and summer months
– During the late afternoon and early evening

Average Number of Tornadoes Per Year

Average Number of Tornadoes Per Month

• 1. Funnel Cloud: extending from wall cloud, but not yet in contact with the ground
• 2. Mature Tornado
• 3. Rope Stage: the dissipating stage
• Tornadoes are dangerous during all stages

Weak
Tornadoes
Strong
Tornadoes
Violent
Tornadoes
11% <1% % of Tornadoes
% of Tornado
Deaths
Duration
88%
<5%
1-10+ minutes
Path Length Up to 3 miles
~30%
20+ minutes
15+ miles
70%
Can exceed 1 hour
50+ miles
Winds <110 mph 110-205mph >205mph

• Tornadoes are always dangerous regardless of shape, size, or color
• Large cities and mountains are just as prone to tornadoes as wide open fields
• Average tornado speed is 30mph, but they can move as fast as 70mph
– Do not attempt to outrun a tornado, find shelter immediately

3
4
5
F Scale Type
0
1
2
Gale
Moderate Weak
Significant
Strength
Weak
Strong
Winds
40-72 mph
73-112 mph
113-157 mph
Severe Strong
Devastating Violent
Incredible Violent
158-206 mph
207-260 mph
261-318 mph

• During periods of severe weather it is important to keep an eye on the sky
• Local television, radio, and the Internet are vital sources of information
• A S.A.M.E NOAA weather radio is essential for immediate watches and warnings