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Severe Weather Guide

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Severe Weather Guide How to Recognize, Identify, and Report Severe Weather Definitions and Terms Watch: conditions are favorable for severe weather Warning: severe ... – PowerPoint PPT presentation

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Title: Severe Weather Guide


1
Severe Weather Guide
  • How to Recognize, Identify, and Report Severe
    Weather

2
Definitions and Terms
  • 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

3
Thunderstorms
  • 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

4
Thunderstorms
  • Developing Stage
  • Rising cumulus clouds strong updraft
  • Little if any precipitation
  • Lasts about 10 minutes
  • Occasional lightning

5
Thunderstorms
  • 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

6
Thunderstorms
  • Dissipating Stage
  • Weakened updraft
  • Rainfall lessens in intensity
  • Lightning and strong winds remain a threat

7
Types of Thunderstorms
  • 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

8
Types of Thunderstorms
  • 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

9
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10
Single Cell Storm
  • 20-30 minutes
  • Rarely turn severe
  • Heavy rainfall and weak tornadoes are still
    possible
  • Poorly organized

11
Single Cell Storm
12
Multicell Cluster Storm
  • 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

13
Multicell Cluster Storm
14
Multicell Cluster Storm
15
Multicell Line Storm
  • 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

16
Multicell Line Storm
17
Multicell Line Storm
18
Multicell Line Storm Bow Echo
19
Multicell Line Storm Bow Echo
20
Supercell Thunderstorm
  • Rarest type of thunderstorm, but the most
    dangerous
  • The updraft rotates (called mesocyclone)
  • Large hail
  • Heavy downpours
  • Strong downbursts
  • Strong to violent tornadoes

21
Supercell Thunderstorm (w/o Tornado)
22
Supercell Thunderstorm (w/Tornado)
23
Supercell Thunderstorm (w/Tornado)
24
Supercell Thunderstorm
25
Dangers of Thunderstorms
  • Flash Floods
  • Lightning
  • Hail
  • Downbursts
  • Tornadoes

26
Flash Floods
  • 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, Dont Drown
  • Get to higher ground immediately

27
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28
Lightning
  • 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

29
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30
Hail
  • 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

31
Hail
  • Sizing Chart
  • Pea 0.25
  • Penny/Dime (Severe Criteria) 0.75
  • Nickel 0.88
  • Quarter 1.00
  • Half Dollar 1.25
  • Ping Pong Ball 1.50
  • Golf ball 1.75
  • Hen Egg 2.00
  • Tennis Ball 2.50
  • Baseball 2.75
  • Grapefruit 4.00
  • Softball 4.50

32
Downbursts
  • 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

33
Downbursts
34
Downbursts
  • 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

35
Tornado Look-A-Likes
  • 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

36
Wall Clouds versus Shelf 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
37
Wall Cloud
38
Wall Cloud
  • 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!

39
Shelf Cloud
40
Roll Cloud
41
Scud Cloud
42
Tornadoes
  • 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

43
Tornadoes
  • 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

44
Average Number of Tornadoes Per Year
45
Average Number of Tornadoes Per Month
46
Tornadoes By Hour of Day
47
Tornado Life Cycle
  • 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

48
Funnel Cloud
49
Mature Stage
50
Rope Tornado
51
Tornado Characteristics
Weak Tornadoes Strong Tornadoes Violent Tornadoes
of Tornadoes 88 11 lt1
of Tornado Deaths lt5 30 70
Duration 1-10 minutes 20 minutes Can exceed 1 hour
Path Length Up to 3 miles 15 miles 50 miles
Winds lt110 mph 110-205mph gt205mph
52
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53
Tornadoes
  • 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

54
Tornado Fujita Scale
F Scale Type Strength Winds
0 Gale Weak 40-72 mph
1 Moderate Weak 73-112 mph
2 Significant Strong 113-157 mph
3 Severe Strong 158-206 mph
4 Devastating Violent 207-260 mph
5 Incredible Violent 261-318 mph
55
Severe Weather Alerts
  • 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
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