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Atmospheric Phenomenon _Weather_

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					Atmospheric Phenomenon
          (Weather)




  Thunderstorms, hurricanes,
  tornados, blizzards, drought
                                     Energy
• Fundamental to understanding weather
• Force
   –   Acts on physical materials
   –   Cannot be seen, rather felt
   –   Tension, compression, shear
   –   Newtons (N) = force necessary to move 1 kg 1m / sec
• Work
   – Done by the expenditure of energy
   – Joules = 1 newton over 1m
         • 10 trillion joules / average thunderstorm
         • 100,000 x that for average hurricane
• Power
   –   Rate at which work is done
   –   Power = joules/sec
   –   1 joules/sec = 1 W
   –   Global energy consumption = 13 TW (TerraWatts)
   –   Global solar flux = 120,000 TW
                    Types of Energy

• Potential
   – Stored energy potentially available
   – Rock on a cliff contains potential energy
• Kinetic
   – Energy of motion
   – Rock falls, gains kinetic E and loses potential E
• Thermal
   – Heat or random motion of atoms and molecules
   – Transferred from one body to another by delta temperature
   – Sensible
       • Heat felt by senses
       • Measured by thermometer
   – Latent
       • Result of phase change
       • Liquid H2O to vapor absorbs heat (latent heat of vaporization)
       • Conversely, vapor to liquid drop releases heat (condensation)
                        Heat Transfer
• Conduction
   – Transfer of heat through atomic or molecular interactions
   – Thermal energy moves from area of higher temp to area of lower temp
   – Coffee to spoon
• Convection
   – Transfer of heat through mass movement of fluid
   – Convection cells
   – Hot fluids rise, cool fluids sink
• Radiation
   –   Electromagnetic energy transferred through wave emission
   –   Oscillations in magnetic and electrical fields
   –   Transfers through vacuum (e.g. space)
   –   Red light emitted by glowing ember
   –   Sun’s light and/or heat
                   Earth’s Energy Balance
•   Electromagnetic energy
     –   Travels in waves @ 186,000mi/sec
     –   Infrared
           •   Involved with global warming
     –   Ultraviolet
           •   Increases with depletion of the ozone
•   Radiation
     –   All matter radiates energy except @ absolute zero temperature
     –   Radiation increases to the 4th power as temp increases
•   Absorption
     –   Related to temp
     –   Cooler object absorbs until a balance is achieved with radiation
     –   Earths energy balance is changing
•   Reflectivity
     –   Varies with color
     –   Clouds reflect 30-90%
     –   30-40% grasslands
     –   10-15% coniferous forests
•   Temperature
     –   Hotter objects emit more energy at shorter wavelengths
     –   Sun emits mostly gamma, x-rays, visible and ultraviolet light
     –   Earth emits mostly infrared radiation
Electromagnetic Spectrum
           Earths Atmosphere

• Composition
  – 77% nitrogen
  – 21% oxygen
  – 2% other (argon, H2O vapor, CO2)
                        Earths Atmosphere
• Structure
   – No well-defined upper limit
   – Mostly below ~100km
   – 6 major layers
       • Exosphere
              – Free-roaming ions that
                may migrate in and out of
                the solar wind
              – Very thin
       • Ionosphere
              – Ionized by solar radiation
       • Thermosphere
       • Mesosphere
              – Meteors burn up
       • Stratosphere
              – Ozone layer
       • Troposphere
              – Where we live
              – Significant < in temp
              – H2O content
      Earths
   atmospheric
   temperature
      profile

•Atmospheric temp
fluctuates w/altitude
•Hottest where Suns
solar energy is not
attenuated by
denser atmosphere
                      Weather Processes
•   Atmospheric pressure (barometric pressure)
     – Weight of column of air
     – Air rises in areas of low atmospheric press
          • Cools and condenses H2O vapor creating clouds and precipitation
     – Air descends in high press areas
          • Drier air results in clear atmospheric conditions
•   Unstable air
     – When lighter, warm air is overlain by denser, cool air
     – Vertical adjustments occur
     – Conditions for thunderstorms
•   Coriolis effect
     – Deflection of air currents caused by rotation of the Earth
     – Right in northern hemi/left in southern hemi
•   Fronts
     – Boundary between cooler and warmer air masses
     – Cold
     – warm
            Hazardous Weather
•   Thunderstorms
•   Hurricanes
•   Tornados
•   Blizzards and Ice Storms
•   Drought
•   Dust and Sand Storms
•   Heat waves
                                  Thunderstorms
• Thunderstorms
  – Lower H2O-laden air mass
  – Temp gradient between
    overlying cooler, dryer air
    & underlying warmer,
    moist air
  – Updrafts
  – Exist during periods where
    updrafts and downdrafts
    produce convective cells
  – Warm air has > moisture
    capacity than cold air
Ocean Currents
•   Severe thunderstorms
     – MCC (Mesoscale Convective
       Complexes)
          • Most common & self perpetuating
     – Squall lines
          • Average 500km long
          • Develop parallel to cold fronts
     – Supercells (single, large updraft area)
          •   Smallest of three
          •   Spawn most tornados
          •   High wind shear and downdrafts
          •   Much damage in short time duration
•   Form when moist,
                                    Thunderstorms
    unstable air is lifted
    vertically into the       major features and circulation patterns
    atmosphere
•   Lifting results in
    condensation and
    the release of
    latent heat
•   Lifting occurs by:
     –   Unequal
         warming of the
         surface of the
         Earth
     –   Orographic
         lifting due to
         topographic
         obstruction of air
         flow
     –   Dynamic lifting
         because of the
         presence of a
         frontal zone
• Greatest incidence in
  SE and parts of Co,                   Thunderstorms
  Az, & NM
• Spatial distribution        Average number of thunderstorm days per year in the US
  suggests extreme
  solar heating is NOT                     (Source: Oklahoma Climatological Survey)
  only requirement for
  thunderstorm
  formation
• Other critical factor
  availability of warm
  moist air
    – Gulf of Mexico
      supplies moist
      maritime tropical air
      masses
    – Relatively unstable
    – Quickly form
      cumulonimbus clouds
• In Co, Az, & NM                     Thunderstorms
  leeward side of Rocky
                            Average number of thunderstorm days per year in the US
  Mountain slopes face
  Sun & absorb more
                                         (Source: Oklahoma Climatological Survey)
  direct solar energy
   – become relatively
     warmer creating
     strong updrafts that
     form into cumulus
     clouds
• Few thunderstorms
  occur along the west
  coast of US
   – dominated by cool
     maritime polar air
     masses which
     suppress
     convectional uplift
     over land
                                   Thunderstorms
                              development of a common air-mass storm
                                          Cumulus Stage
•   Normally develop in late afternoon
     –   Surface heating produces the max number of convection currents
     –   Flagstaffs summer “monsoon” season
•   Three stage life cycle
•   The first stage is called the Cumulus Stage
     –   Oceanic (usually) evaporation creates air mass with high humidity
     –   Parcels of warm, humid air rise and cool to form clusters of puffy white cumulus clouds
     –   Cloud formation due to condensation
     –   Formation releases large quantities of latent heat
•   Added heat energy keeps air inside cloud warmer than air around it
•   Cloud continues to develop as more humid air is added from below
•   Updrafts dominate the circulation within the cloud
         Thunderstorms
                          Mature Stage




•   When the updrafts reach max alt ~12-14 kms, change
    direction 180° becoming downdrafts
•   Storm is in its Mature Stage
     –   Downdrafts = precipitation through collision and coalescence
     –   At its most intense stage of development
     –   Now a cumulonimbus cloud
•   Top of cloud takes on familiar anvil shape
     –   Strong stratospheric winds spread ice crystals in the top of the cloud horizontally
     –   Several kms in diam @ base
     –   Mature T-storm contains heavy rain, thunder, lightning, and wind gusts at the surface
                        Thunderstorms
                                Dissipating Stage


• Mature T-storms decrease in intensity entering the Dissipating
  Stage
   –   After ~1/2 hr
   –   Air currents dominated by downdrafts
   –   Supply of warm, moist air from lower atmos is depleted
   –   Within ~ 1 hr storm is finished and precipitation stops
     Coriolis Effect and Winds Patterns
• Winds are simply
  moving molecules of air
• Subject to Coriolis forces
   – Deflects to the right in
     the Northern hemisphere
     and to the left in the
     Southern hemisphere
   – when viewed along the
     line of motion
• Wind patterns driven
  mostly by Solar heating
       Coriolis Effect and Winds Patterns
• Solar heating on the Earth
  produces 3 major convection
  zones in each hemisphere
• If solar heating were the only
  thing influencing the
  weather, the prevailing winds
  along the Earth's surface
  would either be from the
  North or the South,
  depending on the latitude
• Coriolis force deflects these
  wind flows
    – Strongest at poles weakest at
      equator
       150yrs of typhoon storm
                tracks




•   Follow warm ocean
    currents
•   Coriolis effect
     • Weakest at equator
         keeps rotational
         storms from forming
•   S. Amer. Typhoon gap
     • Catarina
Atlantic hurricane storm tracks
       Cyclone and anticyclone wind patterns
•   The wind flow around high pressure (anticyclonic) systems is clockwise in the Northern
    hemisphere and counterclockwise in the Southern hemisphere
•   The corresponding flow around low pressure (cyclonic) systems is counterclockwise in the
    Northern hemisphere and clockwise in the Southern hemisphere
•   This is a consequence of the Coriolis force
                 Atmospheric Pressure
•   1yd3 of air at MSL pressure & a temperature of 70 F weighs almost exactly 2
    pounds
•   The air in a room 12 ft x 14 ft with an 8-foot ceiling weighs almost exactly 100
    pounds
•   The average air pressure at sea level is about 14.7 psi
•   A column of air 1cm2 , from sea level to the top of the atmosphere, has a mass
    ~1kg and a weight of 2.2 lbs
     – A column 1in2 in cross-section would weigh about 14.7 lb
•   Ave sea-level press is 101.325 kPa (1013.25 mbar, or hPa) or 29.92 in of
    mercury (inHg) or 760 mm (mmHg)
•   The highest barometric press ever recorded on Earth was 1,085.7 hectopascals
    (32.06 inHg) measured in Tonsontsengel, Mongolia on 19 December 2001
•   The lowest non-tornadic atmospheric pressure ever measured was 870 hPa
    (25.69 in), set on 12 October 1979, during Typhoon Tip in the western Pacific
    Ocean
                      this image from September 4,
                      2003
                      shows a beautifully-formed low-
Low-Pressure System   pressure
                      system swirling off the
                      southeastern
                      coast of Greenland,
                      (Jacques Descloitres,
                      MODIS Rapid Response Team,
                      NASA/GSFC) #
                            Tropical Cyclones
•   Characterized by low pressure center & numerous T-storms that produce strong winds,
    flooding rain, and storm surges
•   Fueled by different heat mechanism than other cyclonic windstorms: nor'easters, European
    windstorms, and polar lows
•   Classified as "warm core" storm systems
     –   "tropical" refers to geographic origin & their formation in Maritime Tropical air masses
     –   "cyclone" refers to CCW rotation in the N Hemi and CW rotation in the S Hemi
•   Depending on their location and strength can be referred to as hurricane, typhoon, tropical
    storm, cyclonic storm, tropical depression and simply cyclone
                                       Tropical Cyclone
                                          Major Components
•   Spiral Bands - localized
    areas of tall/deep clouds,
    heavy rain, and high winds
    may extend a few hundred
    kms outward from the
    center of a hurricane
•   Eyewall – area just outside
    eye, usually formed by
    sheer wall of clouds
     –   Most intense precipitation
     –   Most intense winds
•   Eye – calmest part of storm
     –   Hi press near top of
         hurricane causes the air in
         the eye to sink
     –   Why the weather is nice in
         the eye
     –   In contrast, surface press
         near eye is very low
     –   < barometric press >
         storm
The Eye of the Storm
                                              Hurricane
•   The "right side of the storm" is
    defined with respect to the
    storm's motion:
                                             Asymmetry
     –   if the hurricane is moving to the
         west, the right side would be to
         the north of the storm; if the
         hurricane is moving to the
         north, the right side would be to
         the east of the storm, etc.
•   In general, this is because the
    motion of the hurricane also
    contributes to its swirling winds
•   A hurricane with a 90 mph winds
    while stationary would have
    winds up to 100 mph on the right
    side and only 80 mph on the left
    side if it began moving (any
    direction) at 10 mph
     –   Note : forecasting agencies take
         this asymmetry into account
         when stating wind speeds
•   Created by complexes of T-
    storms
     –   Evolve into hurricane strength
         w/the aid of the ocean and

     –
         atmos
         Water must be warm enough to
         provide energy usually > 75 degrees F
                                                   Hurricanes
     –   Warm water provides heat &
         moisture which provides energy
     –   Why hurricanes quickly weaken when
         they travel over land or colder ocean
         waters
•   High humidity in the mid & lower
    troposphere assist in
    development
     –   Reduce amt of evap in clouds & max
         the latent heat released due to
         increased precip
     –   Concentration of latent heat is
         essential to the system
     –   Vertical wind shear, the amount of
         change in the winds direction or
         speed as alt >
•   Wind shear weak
     –   Storms grow vert as latent heat from
         condensation is released above storm
     –   The stronger the wind shear the more
         slanted the storm & more latent heat
         is released and dispersed over a larger
         area
                                                      Hurricanes
     • 5 categories
             – Saffir-Simpson Scale                           Category     Pressure (mb)   Winds (mph)   Surge (ft)
               (at right)
     • Damages                                               Depression                        <39

             – Storm surge                                      T-storm                       39-73
             – Coastal erosion                               Hurricane 1       >980           74-95        5-Apr
             – Wind                                          Hurricane 2      965-980         96-110       8-Jun
                     • Doubling speed =                      Hurricane 3      945-965        111-130      12-Sep
                       8X increase in                        Hurricane 4      920-945        131-155       13-18
                       power
                                                             Hurricane 5       <920           >156          >18
             – Rain driven floods

The standard atmosphere (symbol: atm) is a unit of pressure and
is defined as being precisely equal to 101.325 kPa. The following
non-standard units are equivalent: 760 mmHg (torr), 29.92 inHg,

14.696 PSI, 1013.25 millibars.
   Hurricanes
• Destructive tropical
  cyclone that forms in the
  western Atlantic Ocean
    – Winds > 74 mph
• Usually accompanied by
  electrical storms
    – Typically occur during
      summer & early autumn
• In a day can release the
  amount of energy to
  satisfy the electrical needs
  of the entire US for ~6
  months
   Hurricanes
• Form over warm, tropical
  waters (>80F)
• Lose strength 3 ways
    – Remain stationary and
      siphon off warm waters
    – Move over cooler waters
      to the north
    – Move over ground mass
• Must have sustained
  winds of > 74mi/hr
• Rotating winds around a
  calm eye begin by Coriolis
  Effect
• Cover extensive area
     Storm Surge
• Offshore rise of water
  associated with low
  pressure weather
  systems
• Caused primarily by
  high winds pushing on
  the ocean's surface
• Causes water to pile up
  higher than ordinary
  sea level                 Images from Gulf Coast area during Gustav Sept. 2008
• Low pressure at center
  of system also has a
  small secondary effect,
  as can the bathymetry
  of the water body
                                  Storm Surge
•   It is the combined effect of low pressure and persistent wind over a shallow water body
    which is the most common cause of storm surge flooding problems
•   In areas where there is a significant difference between low tide and high tide, storm
    surges are particularly damaging when they occur at the time of a high tide
Current 2009 North Atlantic storms
Current 2009 North Atlantic storms
•Used to be named
with by lat/ long
     •1953 the
     National
                                      Hurricane Names
     Hurricane Center
                                                Names of Future Atlantic Tropical Storms
     began giving
     women's names        2005       2006             2007               2008              2009        2010
     to tropical storms   Arlene     Alberto           Andrea             Arthur             Ana        Alex
     originating in the
                           Bret       Beryl             Barry             Bertha              Bill     Bonnie
     Atlantic Ocean
     •1979 a new           Cindy      Chris            Chantal           Cristobal         Claudette    Colin

     naming method        Dennis      Debby             Dean               Dolly            Danny      Danielle

     began with men's      Emily     Ernesto             Erin            Edouard             Erika       Earl
     and women's          Franklin   Florence           Felix              Fay               Fred       Fiona
     names being           Gert      Gordon           Gabrielle          Gustav             Grace      Gaston
     alternated           Harvey     Helene           Humberto            Hanna             Henri      Hermine
•Six different lists of    Irene      Isaac             Ingrid             Ike                Ida        Igor
names are now              Jose       Joyce             Jerry           Josephine          Joaquin      Julia
used                      Katrina      Kirk             Karen              Kyle              Kate        Karl
     •Recycled every
                            Lee       Leslie           Lorenzo            Laura              Larry      Lisa
     six years
     •One exception -      Maria     Michael           Melissa            Marco             Mindy      Matthew

     if a storm is         Nate      Nadine             Noel              Nana             Nicholas    Nicole

     especially deadly    Ophelia     Oscar             Olga              Omar              Odette      Otto
     or costly then       Philippe    Patty             Pablo            Paloma             Peter       Paula
     that name is           Rita      Rafael          Rebekah             Rene               Rose      Richard
     retired from the      Stan       Sandy           Sebastien            Sally             Sam        Shary
     list and a new
                          Tammy       Tony              Tanya             Teddy             Teresa     Tomas
     name is selected
     to replace it         Vince     Valerie             Van              Vicky             Victor     Virginie
                          Wilma      William           Wendy             Wilfred            Wanda      Walter
           •   Tornados
Tornados        – From 1992-2002
                  killed aver. of 57
                  people/yr
                – Form under large
                  barometric
                  pressure
                  gradients
                – Increased danger
                  because of
                  material inside
                  spinning vortex
                – Funnel clouds vs
                  tornado (vortex
                  must touch
                  ground)
                – Fujita or F-scale
                  classification
                  system
                     • Based on post
                       storm
                       damage
                       survey
                – Central U.S. has
                  more than
                  anywhere else
• A violent rotating
  column of air in
  contact with the
  ground and a
                          Tornados
  cumliform cloud
    – Condensation
      funnel
    – Family
         • Multiple
           events from
           same storm
    – Outbreak
         • No break in
           activity
• Types
    –   Multiple vortex
    –   Satellite
    –   Waterspout
    –   Landspout
                         •   Tornadoes often develop from a class
Supercell Relationship       of thunderstorms known as
                             supercells
                         •   Supercells contain mesocyclones
                         •   An area of organized rotation a few
                             miles up in the atmosphere, usually
                             1–6 miles (2–10 km) across
                         •   Most tornadoes from supercells
                             follow a recognizable life cycle
                              – Formation
                              – Maturity
                              – Dissapating
                         •   Dissapation begins when > rainfall
                             drags an area of quickly descending
                             air known as the rear flank downdraft
                             (RFD)
                         •   RFD completely wraps around and
                             chokes off the tornado's air supply
                              – Vortex weakens
                              – Becomes thin and rope-like
                              – During this stage the shape of the
                                tornado becomes highly influenced
                                by the winds of the parent storm,
                                and can be blown into fantastic
                                patterns.
Multiple Vortex Tornado
      Dallas, Texas, 1957

                            •Tornado in which two or
                            more columns of
                            spinning air rotate
                            around a common center
                            •Very often observed in
                            intense tornadoes
                            •Satellite tornado is a
                            weaker tornado which
                            forms very near a large,
                            strong tornado contained
                            within the same
                            mesocyclone
                            •The satellite tornado
                            may appear to "orbit"
                            the larger tornado
•Tornados are not
necessarily visible
                                  Funnel Clouds
•Intense low pressure
caused by high wind speeds
& rapid rotation usually
causes water vapor in the
air to become visible as a
funnel cloud or condensation
funnel
•Most tornadoes produce
strong winds at the surface
while the visible funnel is
still above the ground
•It can be difficult to discern
the difference between a
funnel cloud and a tornado
from a distance
• Usually travel NE
                              Tornados
• Most have wind speeds
  between 40 mph &
  110 mph
• ~ 250 ft across
• Travel a few mi before
  dissipating
   – Few attain wind speeds
     of more than 300 mph
   – More than a mile
     across
   – Travel more than
     10’s/100’s of mi
• Observed on every
  continent except
  Antarctica
      Tornados
– Spring in the Central Plains, t-
  storms frequently develop along a
  "dryline,“
    • Separates very warm, moist air to
      the E from hot, dry air to the W
– Along the Front Range, Texas
  panhandle, and southern High
  Plains, t-storms frequently form as
  air near the ground flows
  "upslope" toward higher terrain
    • If other favorable conditions exist,
      these t-storms can produce
      tornadoes
– Occasionally accompany tropical
  storms and hurricanes that move
  over land
    • Most common to the right and
      ahead of the path of the storm
      center as it comes onshore
                  Tornado Alley

– Area of U.S.
  likely to see
  tornadoes
– Highest
  density of
  storms in
  world
            – Storm spotters
Detection       • There are more
                  than 230,000
                  trained Skywarn
                  weather spotters
                  across the US
            – Doppler radar
                • Measures
                  motion
                • Green indicates
                  areas where the
                  precip is moving
                  towards the
                  radar dish
                • Red areas are
                  moving away
                • Radar is in the
                  bottom right
                  corner
            – Adjacent areas of
              bright green and
              bright red are
              mesocyclonic areas
              and usually
              indicate an
              imminent or
              occurring tornado
                                  Fujita Scale
F-Scale
   Num     Intensity Phrase       Wind Speed                   Type of Damage Done
    ber
                                                Some damage to chimneys; breaks branches off trees;
  F0          Gale tornado         40-72 mph        pushes over shallow-rooted trees; damages sign
                                                                       boards.
                                                   The lower limit is the beginning of hurricane wind
                                                        speed; peels surface off roofs; mobile homes
  F1        Moderate tornado       73-112 mph          pushed off foundations or overturned; moving
                                                     autos pushed off the roads; attached garages may
                                                                         be destroyed.
                                                  Considerable damage. Roofs torn off frame houses;
                                                     mobile homes demolished; boxcars pushed over;
  F2       Significant tornado    113-157 mph
                                                       large trees snapped or uprooted; light object
                                                                    missiles generated.
                                                Roof and some walls torn off well constructed houses;
  F3         Severe tornado       158-206 mph
                                                      trains overturned; most trees in fores uprooted
                                                Well-constructed houses leveled; structures with weak
  F4      Devastating tornado     207-260 mph        foundations blown off some distance; cars thrown
                                                               and large missiles generated.
                                                 Strong frame houses lifted off foundations and carried
                                                     considerable distances to disintegrate; automobile
  F5       Incredible tornado     261-318 mph         sized missiles fly through the air in excess of 100
                                                      meters; trees debarked; steel re-inforced concrete
                                                                  structures badly damaged.
                                                These winds are very unlikely. The small area of damage
                                                         they might produce would probably not be
                                                     recognizable along with the mess produced by F4
                                                       and F5 wind that would surround the F6 winds.
                                                      Missiles, such as cars and refrigerators would do
  F6      Inconceivable tornado   319-379 mph
                                                        serious secondary damage that could not be
                                                    directly identified as F6 damage. If this level is ever
                                                       achieved, evidence for it might only be found in
                                                       some manner of ground swirl pattern, for it may
                                                      never be identifiable through engineering studies
 – Weak tornadoes
     • Form over warm water
 – Most common along the Gulf Coast & SE states
 – In W US occur with cold late fall or late winter storms
     • A time when you least expect tornado development
 – Occasionally move inland
     • May become tornadoes




Waterspouts
Mitigation

      • Forecasting

      • Prediction

      • Mitigation
Mitigation

      • Forecasting
         – Behavior unpredictable
         – Models aren’t perfect
      • Prediction
         – Doppler radar
         – Geosynchronous satellites
         – Climate change?
      • Mitigation
         –   Preparedness
         –   Evacuations
         –   Warning systems
         –   Zoning laws
         –   Building codes
         –   Flood and control systems
                                  Myths
• Opening windows will lessen the damage caused by the tornado
    – Low pressure but not enough to cause implosion
• Highway overpasses provide adequate shelter from tornadoes
    – On the contrary, a highway overpass is a dangerous place during a tornado
    – The small area under the overpasses is believed to cause a wind tunnel effect
• Areas which people believe to be protected from tornadoes like a major
  river, a hill or mountain
    – Tornadoes have been known to cross major rivers, climb mountains, and affect
      valleys
    – As a general rule, no area is "safe" from tornadoes
• The southwest corner of a basement provides the most protection during
  a tornado
    – The safest place is the side or corner of an underground room opposite the
      tornado's direction of approach (usually the northeast corner), or the central-
      most room on the lowest floor
        Homework – pick one
               Due Tuesday

• Tri_state Tornado
• Daultipur-Salturia Tornado in
  Bangladesh
• Super Outbreak
• 1999 Oklahoma Outbreak
                              Blizzards
• Severe winter storms with:
    – Blowing snow
    – Wind
    – Very low visibilities
• Heavy snowfalls & severe cold not required
    – Winds pick up snow that has already fallen
• Officially, National Weather Service defines a blizzard as large amounts
  of falling OR blowing snow with winds in excess of 35 mph and visibilities
  of less than 1/4 of a mile for an extended period of time (> than 3 hrs)
• NWS may issue
    – "Blizzard Warning“
    – Or less severe, but still dangerous, "Winter storm watch”

•
         What makes a winter storm?

• Cold Air
   – Below freezing temps in clouds & near ground are necessary to make
     snow and/or ice
• Moisture
   – To form clouds and precipitation
   – Air blowing across a body of water, such as a large lake or the ocean
• Lift
   – To raise the moist air to form clouds & cause precipitation
   – Warm air colliding with cold being forced to rise over the cold dome
         • Boundary between the warm and cold air masses is called a front
   – Air flowing up a mountainside
                      Blizzards
                    Winter Deaths


• Related to ice and snow:
   – About 70% occur in automobiles
   – About 25% are people caught out in the storm
   – Majority are males over 40 years old
• Related to exposure to cold:
   – 50% are people over 60 years old
   – Over 75% are males
   – About 20% occur in the home
                                Blizzards
                              Winter Deaths

• Frostbite
   – Damage to body tissue caused by that tissue being frozen
   – Causes loss of feeling and a white or pale appearance in extremities
       • fingers, toes, ear lobes, or the tip of the nose
• Hypothermia
   – Low Body Temperature
   – Uncontrollable shivering, memory loss, disorientation, incoherence, slurred
     speech, drowsiness, and apparent exhaustion
   – Warm the body core first
   – Do not warm extremities (arms and legs) first as this drives cold blood
     toward heart & can lead to heart failure
                           Notable Blizzards
•   The Great Blizzard of 1888
     –   Paralyzed the NE US for several days
     –   400 people were killed
     –   200 ships were sunk
     –   Snowdrifts 15 to 50 ft
•   The Midwestern “Armistice Day Blizzard” in 1940
     –   Caught many people off guard with rapid & extreme temperature
         change
     –   60 °F in the morning by noon snowing heavily
     –   Caught unprepared died by freezing to death in the snow and
         trapped in cars
     –   154 people died
•   “Storm of the Century” U.S in 1993
     –   105 yrs to the day (March 12) after Great Blizzard of 1888
     –   Snow over 26 states as far north as Canada and as far south as
         Mexico
     –   In many southern U.S. areas (Alabama, etc.) more snow fell than in
         an entire winter
     –   Spawned 15 tornadoes in Florida
     –   Affected at least 1/2 U.S. population
     –   270 people died
     –   48 were reported missing at sea
                       Drought
• Extended period of unusually low precipitation producing a
  temporary shortage of water
• 1 billion people live in common drought regions
• 100 million people are threatened by crop failure due to
  drought
• Effects more people than any other natural hazard in U.S.
• Causes >$6-8b in losses/yr
• SW in middle of 15yr drought cycle
• Water levels in reservoirs at lowest point in decades
      Natural Service Functions
• Lightning started wildfires
• Wind culls diseased trees
• Snowpack is most important source of runoff
  and aquifer recharge
• Spring floods deliver nutrient rich soils,
  cleanse habitat
• Rains water crops and provide percolating
  waters to soils

				
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posted:1/29/2012
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