Title: Severe and Unusual Weather ESAS 1115
1Severe and Unusual Weather ESAS 1115
- Spotter Training and Radar Meteorology
- Part 1 Introduction to Severe Thunderstorms
2Meteorological 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
3Convective HazardsWind, Hail, Floods, Lightning,
Tornadoes
4Severe Thunderstorms are Severe
Many times, the media uses the word severe when
the storm is something less than the actual
meaning of severe.
5Severe 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
6Lightning
7Lightning
25 million CG lightning strikes per year in the
US making it the deadliest aspect of
thunderstorms
8Lightning Safety
- Lightning Stats
- Lightning Safety Video
- Lightning Safety Tips
9Flash 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
10Flash Flood Threat
11Flash Floods Turn Around - Dont Drown
12Hail Big Chunks o Ice
13Tarrant 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)
14We Know First Hand
15Damaging Winds
- Strong outflow from a thunderstorm enhanced by
evaporative cooling and downward momentum
transfer
16Downbursts
- A strong and potentially destructive thunderstorm
downdraft - Microbursts are less than 2.5 miles in diameter
- Macrobursts are greater than 2.5 miles
17Rain Foot and Dust Foot
18Dust Foot
19Microbursts
20Aviation Hazards
21Danger 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
22Beaufort Scale
Winds based on visual observations
23First Microburst
24Microburst within a Macroburst
25Microbursts
26Microburst Evolution
27Tornado 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
28Tornado 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
29EF0, 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
30EF2, 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
31EF4, 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
32Rating a Tornado
33Wind 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
34Swirl Marks