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Severe and Unusual Weather ESAS 1115

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Title: Severe and Unusual Weather ESAS 1115


1
Severe and Unusual Weather ESAS 1115
  • Spotter Training and Radar Meteorology
  • Part 1 Introduction to Severe Thunderstorms

2
Meteorological Sensors
  • Two types of two types of sensors
  • Remote vs. In-situ
  • Active vs. Passive
  • Our passive eyes can only see features of the
    storm
  • In order to see the inner workings of a
    thunderstorm, and to understand it better, we
    need an active remote sensor weather radar
  • Radar will allow us to interrogate information
    about the storm by detecting precipitation and
    wind information within

3
Convective HazardsWind, Hail, Floods, Lightning,
Tornadoes
4
Severe Thunderstorms are Severe
Many times, the media uses the word severe when
the storm is something less than the actual
meaning of severe.
5
Severe Thunderstorm Criteria
  • Hail greater than ¾ in diameter
  • Winds greater than 50 kts (58 mph)
  • Tornadoes
  • Lightning, although posing the greatest threat to
    life, is not a criterion to determining whether
    or not a storm is severe

6
Lightning
7
Lightning
25 million CG lightning strikes per year in the
US making it the deadliest aspect of
thunderstorms
8
Lightning Safety
  • Lightning Stats
  • Lightning Safety Video
  • Lightning Safety Tips

9
Flash Floods Turn Around Dont Drown
  • Water is an incompressible fluid
  • 1000 kg/m3
  • Results in buoyancy 2 feet of water can move an
    SUV
  • Kills more people than lightning more than 100
    annually in the US.
  • Flash flooding vs. river flooding

10
Flash Flood Threat
11
Flash Floods Turn Around - Dont Drown
12
Hail Big Chunks o Ice
13
Tarrant County, TX May 5, 1995
  • 10,000 people at Mayfest
  • Baseball hail 10 miles wide50 miles long
  • 14 people killed by flooding and collapsed roofs
  • 2 billion (estimated)

14
We Know First Hand
15
Damaging Winds
  • Strong outflow from a thunderstorm enhanced by
    evaporative cooling and downward momentum
    transfer

16
Downbursts
  • A strong and potentially destructive thunderstorm
    downdraft
  • Microbursts are less than 2.5 miles in diameter
  • Macrobursts are greater than 2.5 miles

17
Rain Foot and Dust Foot
18
Dust Foot
19
Microbursts
20
Aviation Hazards
21
Danger on Takeoff and Landing
  • On the glide path, too much lift is generated
    with headwind gain
  • With the loss of a headwind, lift is limited

22
Beaufort Scale
Winds based on visual observations
23
First Microburst
24
Microburst within a Macroburst
25
Microbursts
26
Microburst Evolution
27
Tornado and Hail Climatology
There are more than 1000 tornadoes in the US per
year. Hail results in over 1 billion of damage
annually.
Harold Brooks - NSSL
28
Tornado Threats
  • Violently rotating column of air in contact with
    the ground and pendant from a cumulonimbus cloud
    (thunderstorm)
  • Tornadoes are ranked on the Enhanced Fujita
    damage scale from EF0-EF5
  • Appearance is deceiving with small tornadoes
    sometimes having high destruction potential and
    large tornadoes having low potential

29
EF0, EF1 Weak Tornadoes
  • Approximately 70 of tornadoes are in this
    category
  • Well-built houses offer adequate safety for these
    tornadoes
  • Cars and mobile homes are still very vulnerable
    to these tornadoes
  • Wind speeds65 110 mph

30
EF2, EF3 Strong Tornadoes
  • Approximately 28 of all tornadoes are considered
    strong
  • Well-built houses will be severely damaged but
    still can provide adequate life-protection
  • Wind speeds111 165 mph

31
EF4, EF5 Violent Tornadoes
  • Only 2 of all tornadoes are violent
  • Will completely level a well-built house
  • The last EF-5s to hit the US were May 3, 1999
    (Moore, OK,) May 24, 2007 (Greensburg, KS,) and
    May 25, 2008 (Parkersburg, IA.)
  • Wind speeds166 - 200 mph

32
Rating a Tornado
33
Wind Damage vs Tornado Damage
  • Microburst
  • Damage is divergent
  • Large or diffuse area
  • No signs of rotation
  • Tornado
  • Damage is convergent
  • Narrow path
  • Rotation about vertical axis

34
Swirl Marks
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