Ch. 19 Tornadoes

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tornadoes &notes from 3/29-end


• Tornado: intensely rotating column of air touching/contacting the ground
• You can tell b/c there is debris rotating on the ground
• tornado made of: debris and cloud
• you can have though a rotating column of air w/o cloud!! Esp if you can see debris on ground
• Northern HEMI=rotating counter clockwise
o (if it's bright behind it, and the Flanking line is being wrapped up, you still have to keep the intensity of the cloud in mind because it could start to reform again)
• Tornado: violently rotating column of air rotating under a cumulonimbus cloud


formation of a tornado that occurs near the time the supercell''s forward and rear flank downdraft meet under mesocyclone

Double Vortex Stretching

• Wind is stronger up higher and weaker close to ground
• indicates strong wind speed, hear w/ height
• one vortex that was going as a horizontal roll and a strong updraft comes and forces it up and now you have 2 vortices that are tilted vertically, stretched it, and vorticity increases
o think of ice skaters rotating on ice
• vertical wind speed shear, wind simply getting stronger w/ height just off ground—answer to what causes it!

Conservation of Angular Momentum

air stretched in narrower and narrower column will rotate faster and faster
• Wall cloud: isolated lowering of cloud base in vicinity of mesocyclone (strongest updraft) you can have wall cloud w/o mesocyclone
• mesocyclone w/in a tornado radius gets smaller and starts to spin faster
• Whats happeing in that area?
o There is updraft, as pressure decreases in center and air is brought into surface convergance and rapidly brought up, air is ingested into storm

Supercell Tornadoes

• Double Vortex Stretching (titlting)
• stretching and coservation of angular momentum
• mesocylcomnes (less tha 20% produce tornadoes)
• tornadoes
• supercell waterspouts (covered later)
o most come as result of very disorganized cloud band, many aren't even supercells or thunderstorms

Suction Vortices

small extremely violent rotating air columns embedded w/in rotating circulation of large tornadoes
a result of a downdraft being created among the rotating updraft that makes a tornado very wide developing suction vortices
the most severe winds happen here

more tornadoes can result in Tornado families

Tri-State Tornado 1925

• March 18, 1925
• worst tornado in US history
• track length 179 miles
• avg forward speed: 60-65 mph
• avg width in MO: 1/4 mi
• "" in IL: 1/2-1 mi
• killed 695
• injured 2,027
• damage: $16.5 million


measures how unstable the atmos is and how strong a thunderstorm's updraft will be
higher CAPE=higher chance for severe thunderstorms

Non-Supercell Tornadoes

• landspouts
o non-supercell (non-Mesocycloe)
o thunderstorms
o often on frontal boundaries
• Tropical cyclone Related Tornadoes
o right forward side of tropical cyclone
o embedded w/in rainbands
• ATX has history of these
• difficult to see
• very quick moving


• tornado over the water
• "fair" weather waterspouts
o cumulus congestus cloud lines (not necessarily rain producing)
o weak short lived waterspouts
o huge #!
• supercell waterspouts
o cumulonimbus clouds
o associated w/ supercells/ mesocyclones longer lived/ stronger tornadoes
o smaller #

Other Tornado-like Vorticies

• Gustnadoes
o short lived and weak
o often on gust front/outflow boundary
o circulation w/in boundary/friction layer
• cold air funnels
o develop from elevated convective clouds that develop over colder air
o often form under cumulous clouds in the circulation of large, upper air cut off lows
• dust devils
o associated w/ dry convection (hot surfaces)

Tornado Stats

• "tornado alley of USA
• only 25% of all tornadoes globally on avg are outside US

World Tornado Climatology

• you gotta have maritime tropical air, they occur on boundaries (warm moist air, latent heat available)
• you gotta have upper air wind pattern to ensure wind drafts
• longer path linked to more damaging tornadoes

Tornado Detection

• Storm spotters/ storm chasers
• WSR88D Doppler radar (velocity mode)
• surface observations
o they are pretty widely separated when it comes down to scale of tornado
• DOWs (doppler on wheels)
o University of Oklahoma

Storm Chasers vs. Spotters

• Storm chaseres vs. storm spotters diff= spotters stay in one spot, chasers follow tornado, can be very dangerous, beneficial b/c like Dallas tornadoes, could get live feed
• basics of storm spotting

Tornado Forcasting

• Hourly surface analysis charts
• constant height charts
• thermodynamic diagrams
• hodographs
• comp models
• composite charts
• SPC severe weather outlooks/guidance
• Atmospheric Stability Indices:
o CAPE (j/kg)
o Lifted Index (degrees C)
o storm relative helicity (m2/s2)
o energy helicity Index

Post Storm Surveys

• Was the damage caused by a tornado or by straightline winds?
• ground & Aerial surveys
• construction diff & standards
• general rule of thumb:
• convergent damage patter=tornado
• divergent damage patter=straightline winds

Tornado Strength

• weak tornadoes: page 26
o 80% of all US tornadoes
• strong tornadoes:
o 19% of all tornadoes
o less than 30% US fatalities
• Violent:
o 1% of all US tornadoes
o 70% of all fatalities
o 60 min or more
o 200-318 mph


• EF0—KNOW TYPES OF DAMAGES, first bold in supp text
o light damage
o 65-85 mph wind—3 second gust
o branches broken
o signs damaged


o moderate damage
o 86-110 mph
o trees snapped
o shingles blown off
o large signs bent
o windows broken


o Considerable damage
o 111-135 mph
o large trees uprooted
o roofs torn off buildings
o outbuildings/barns destroyed
o cars scooted off highways
o increasing danger/flying debris


o severe damage
o 136-165 mph
o extreme danger from flying debris
o frame home exterior walls blown down
o homes shifted slightly off foundations
o cars become airborne for short distances
o interior walls generally left standing


o devastating damage
o 166-200 mph
o frame homes reduced to foundation as poles of debris immediate downwind
o cars airborne considerable distances
o skyscrapers twisted
o effects of flying debris become spectacular
o little above ground shelter
o suction vortices appear


o incredible damage
o 201-318 mph wind
o frame homes disintegrate w/ debris carried downwind over a wide area (foundation left bare)
o car/trucks airborne ½ mile or more and reduced to chasses and wrapped around objects
o considerable damage to steel reinforced buildings
o well developed suction vortices common

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