http:www.nssl.noaa.govNWSTornado

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Horizontal spinning
Picked up by updraft
Rotating updraft

• Often obscured by rain or clouds
• May not be visible until dust picked up

- Dark, greenish sky - Wall cloud - Large hail -
Loud roar (like train)
http//www.nssl.noaa.gov/NWSTornado/
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Most tornadoes occur east of the Rockies, but
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not always

• California tornadoes
• - Do occur, especially Central Valley/Los Angeles
• - Usually F0 or F1 F2 rare
• F4 or F5 never observed
• Example
• 1998 Sunnyvale/Los Altos tornadoes

1998 Los Altos (F1 or F2)
Looking up at tornado if looking down the
tornado is rotating clockwise
http//tornado.sfsu.edu/geosciences/StormChasing/c
ases/Sunnyvale/Sunnyvale.html
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http//www.la.mvla.net/SpEvents/pics/Tornado/torna
do.htm
Damage (Los Altos and LAHS)
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Kathleen Klein
Laurence Kerckhoff
2/2005 - Sacramento
- Not clear if these are supercell tornadoes
http//tornado.sfsu.edu/SacTornado/SacTornado.html
Matthew Adams
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Detection and prediction
Prediction Conditions that produce tornadoes are
known But not all supercells produce
tornadoes Some are extremely productive why?
Detection New weather radars can spot
tornadoes Need to improve identification of
pre-tornado patterns to increase warning
time Need to install radars and training
everywhere
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Tornado safety
Tornado watch conditions are right for
tornadoes Tornado warning tornado has been
sighted by people or radar Not much time to make
decisions use advance planning Flying debris
(wood, drywall, cows, etc) is the biggest
danger In car - FEMA says stop and get out to
hide in building or ditch. - typically, tornadoes
may travel 20-30 mph
http//www.nssl.noaa.gov/edu/tornado
Note winds strong enough to lift a cow would
likely knock a truck off the road from the
movie Twister (1999)
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Go to an interior room without windows
bathrooms, closets avoid flying glass objects
that puncture exterior walls crawl under sturdy
objects Mobile homes are dangerous supposed to
leave them Avoid large rooms with no interior
support (auditoriums, shopping malls, PS 130, etc)
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1 person killed 12 injured
Highway overpasses and tornadoes - the myth. In
April 1991, a news team took a video of a tornado
from an overpass they survived Many people saw
this video In 1999, Okalahoma City was hit by a
tornado many people hid under overpasses The
tornado hit 3 overpasses at each one someone
dies and many were injured, some badly A later
study showed that overpasses are more dangerous
than elsewhere.
See http//www.srh.noaa.gov/oun/papers/overpass.ht
ml
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Salt Lake City, 1999
Some more pictures
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Waterspouts fair-weather - convection
driven - ground to cloud - updraft under
rain - often move slowly - near vertical
funnel - often in groups - warm water,
cool air, and low winds - fairly
common Tornadic - a tornado over water -
cloud to ground - can move quickly - rare
Can be dangerous to small boats
http//www.srh.noaa.gov/eyw/HTML/spoutweb.htm
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Dust devils
Dust devils Driven by hot air rising May spin in
any direction Can occur over fires as well
Dust devil tracks on Mars
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http//rams.atmos.colostate.edu/newcotton-home.htm
l
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Hurricanes
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Hurricane formation

• Grow from thunderstorms
• Require 26.5 C/81 F water temperature
• Colder water gt weakens
• Landgt weakens
• High humidity in lower and middle troposphere
• Increase precipitation
• Release latent heat as vapor condenses
• Low wind shear
• Wind similar speed and directions at all
  elevations
• Released heat stays in storm

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Stages of formation (Atlantic)

• Cluster of thunderstorms (tropical disturbance)
• Intertropical convergence zone
• Frontal system from north
• Easterly wave from Western Africa (most
  hurricanes)
• With favorable conditions, becomes organized
• Rotation (counter-clockwise in Northern
  Hemisphere) Coriolis force
• Release of latent heat provide energy and updraft
• This heat causes more inflow and more heat
  release (feedback)
• Unfavorable conditions weaken or destroy
  hurricanes
• Strong high-level winds
• Lack of warm moist air
• Move over cold water
• Move over land
• Dry, high-pressure air

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Hurricane anatomy

• Eye center
• Sinking air
• Low winds
• Eye wall
• Ring of tall thunderstorms
• Heavy rains and strong wind
• Highest winds where rotation combines with
  forward motion
• Spiral rain bands
• Wind and rain
• Less than eye wall

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Storm surge

• Rise in ocean level caused by hurricane
• - driven by wind (mostly)
• - rises due to low air pressure
• - greatest on the right side of storm (Northern
  hemisphere left in Southern)
• - worst effects when combined with astronomical
  high tide
• 2. Causes the most damage and death
• - perhaps 80-150 km wide
• - bad for low-lying coastlines

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Naming and classification of hurricanes (Saffir-Si
mpson scale quantify strength and damage)
37 km (23 mph) tropical depression receives
name started in World War II (military style
Able, Baker, Charlie) 1953 switched to female
names alternate male/female in late 1970s 199
km (74) mph hurricane (category 1)
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Hurricane occurrence

• Perhaps 20-30 hurricanes per year, worldwide, on
  average
• 6-8 per year in Atlantic
• More in Western Pacific (typhoons)
• Frequency varies considerably
• Depends on climate
• Regional weather (wind shear, etc)
• Water temperature

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• Hurricane tracks
• Driven by regional winds
• Varies, depending on weather systems
• Can be predicted up to 3 days in advance, mostly
  (not perfect)
• Atlantic
• -West coast of Africa gt Carribbean and US East
  coast
• Western Carribbean gt eastern Mexico, Central
  America, US Gulf
• Gulf of Mexico gt Mexico, US gulf coast