-one having at least one of the following:

1)large hail with a diameter of at least three-quarters of an inch

2)surface wind gusts of 50knots (58mi/hr)

3)tornadoes

-tend to form in a region where there is limited wind shear....  ie. where the wind speed and wind direction do not abruptly change with increasing height above the surface.

-regular storm... not too intense

1)CUMULUS STAGE (growth stage)

-as a parcel of warm, humid air rises, it cools and condenses into a single cumulus cloud or a cluster of clouds

-transformation of water vapor into liquid or solid cloud particles releases large quantities of latent heat

-eventually updrafts are unable to keep heavy particles suspended as they grow to big

2)MATURE STAGE

-the appearance of the downdraft marks the beginning of the mature stage

-up and down draft in the thunderstorm together constitute the cell

 -during this stage, cloud is biggest and most intense

-gust front - the surface boundary that separates the advancing cooler air from the surrounding warmer air.. it enhances the cloud's updraft as it is a cold mass that pushes more air up

3)DISSIPATING STAGE

-occurs after about 15-30min of mature stage

-occurs when the updrafts weaken as the gust front moves away from the storm and no longer enhances the updrafts.

**a single ordinary thunderstorm may go through its three stages in one hour or less

*thunderstorms can bring great cooling with downdrafts

streamlines - lines that show the windflow pattern

- useful because they show wheresurface air converges and diverges

-tropical/easterly wave -a migratory wave-like disturbance in the tropical easterlies. Tropical waves occasionally intensify into tropical cyclones... also called easterly waves

-travel from east to west and have wavelengths on the order of 2500km

-an intense storm of tropical origin with sustained winds exceeding 64 knots (74 mi/hr), which forms over the warm northern Atlantic and eastern North Pacific oceans.

***in the western North Pacific, the same storm is called a TYPHOON, in India, a CYCLONE, and in Australia, a TROPICAL CYCLONE.

****By international agreement, tropical cyclone is the general term for all hurrican-type storms that originate over tropical waters.

the area of broken clouds at the center

-within eye, winds are light and clouds are mainly broken... the surface air pressure is very low... nearly 955mb

***average diameter is about 500km for a hurricane

the clouds align themselved into spiraling bands that awirl in toward the storm's center, where they wrap themselves around the eye

***surface winds incrrease in speed as they blow counterclockwise and inward toward this center

adjacent to the eye, is a ring of intense thunderstorms that whirl around the storm's center and may extend upward to almost 18km

-within eyewall, we find the heaviest precipitation and the strongest winds, which, in this storm, are 105 knots, with peak gusts of 120 knots.

-form over tropical waters where winds are light, humidity is high and deep, and the surface water temperature is warm (26.5C or greater over a large area)

-these conditions usually prevail overr the tropical North Atlantic and North Pacific oceans during the summer and early fall... hence huricane season generally runs from June-Nov

-for hurricanes to converge, need a converging wind... therefore hurricanes generally form around 5-20 latitude where there is a coriolis force

-hurricane formation requires a trigger... usually it is a tropical wave or a wave that forms over Africa.... more powerful when western africa is wet.

-also requires the lack of a trade-wind inversion... also hurricanes do not form when upper level winds are strong

-the energy for a hurricane comes from the direct transfer of sensible heat and latent heat from the warm ocean surface

-a cluster of thunderstorms mmust become organized around a central area of surface low pressure... not clear how this occurs

Theory:

-weak trade wind inversion and thunderstorms start to organize along the ITCZ, or along a tropical wave

-in the deep, moist conditionally unstable environment, a huge amount of latent heat is released inside the clouds during condensation.

-the process warms the air aloft, causing the temperature near the cluster of thunderstorms to be much higher than the air temperature atthe same level farther away

-this warming of the air aloft causes a region of higher pressure to form in the upper troposhepere

-this situation causes a horizontal pressure gradient aloft that induces the air aloft to move outward, away from the region of higher pressure in the anvils of the cumulonimbus clouds

-this causes surface pressure to drop

-driving force behind hurricane is similar to that of a heat engine. Heat is taken in at a high temperature, converted into work, then ejected at a low temperature.

**max strength of a hurricane is proportional to the difference between the temperatures entering and exiting.

-if the hurricane remains over warm water, it may survive for a long time

-most last for less that a week

-hurricanes weaken rapidly when they travel over colder water and lose their heat source

-also dissipate when they move over landmass... lose energy source and encounter friction

tropical disturbance/tropical depression/tropical storm/hurricane

-initially, a tropical disturbance shows up as a mass of thunderstorms with only slight wind ciruculation

-becomes a tropical depression when winds increase to b/w 20 and 34 knots

-when isobars are packed and winds are b/w 35-64 knots, depression becomes tropical storm (at this point, it gets a name)

-only becomes a hurricane if speed exceeds 64 knots.

-generally steered by easterly winds and move west for about a week or so.

-can swing poleward at the subtropical high

-movement based on environment and hurricane structure... .known for unpredictable movements

-Hawaii seems to be in a Hurricane path... but the storms almost always fizzle out before getting there

-alphabetical... season's first storm is A, then B,

-women's names were only used

-but now all sorts of names are used

-if exceeds alphabet, greek alphabet is used.

-when a hurricane is approaching from the south, its highest winds are usually on its eastern (right) side

-this is because the winds that push the storm along are added on the east side

-even though a hurricane may be moving north, net transfer of water is from east to west

spiral - an idealized description of the way the wind-driven ocean currents vary with depth.

-in the atmosphere it represents the way the winds vary from the surface up through the friction layer or planetary boundary layer

transport - net surface water transport due tothe Edman spiral. In the Northern Hemisphere the transport is 90 degrees to the right of the surface wind direction

-the high winds of a hurricane also generate large waves (10-15m).

-these waves move OUTWARDS, waay from the storm, in the form of swells that carry the storm's energy to distant beaches

-a scale based on actual conditions at some time during the life of a storm

-developped in an effort to estimate the possible damage a hurrican'es sustained winds and storm surge could do to a coastal area

-ranges 1-5, major hurricanes are classified as category 3+

-although the high winds of a hurricane can evastate a region, considerable damage may also occur from hurricane spawned tornadoes

-about 1/4 of the hurricanes that strike the USA produce tornadoes

-in 2004, six tropical systems produced just over300 tornadoes

-many are small eddies, causing the most damage, lasting for about 10 seconds

-until 2005, annual death toll from hurricanes in USA averaged less than 50 persons..... mostly due to flooding

-in hurricane katrina, more than 1300 people died

1969

-one of most intense to reach coast of USA in 20th CE

-pressure 909mb!

-was a category 5... 200 lives

-1989

-category 4, hit sSouth Carolina... origin Africa

-knocked out power, flooded streets, and caused 7billion in destruction

-1992

-one of strongest to hit florida in 100 years

-estimate peak winds at 174 knots... (200 mi/hr)

-one of costliest to ever hit USA

-30 billion in damage

-2004

-stron category 3

-5 meter storm surge

-hit land, did damage, went back to gulf and regained strength, then hit land again

-2005

-most costly storm to ever hit US

-passed over LOOP CURRENT, which allowed it to intensify

-was a category 5

-had an EYEWALL REPLACEMENT

-made landfall as a category 3

-levees gave way in New Orleans... water up to 20 feet deep invaded a large part of the city

75 BILLION!!

Before era of satellites and radar, catastrphic losses of life had occurred..

-in 1900, more than 6000 people lost their lives when a hurricane slammed into Galveston Texas with a huge storm surge.

***smalle compared to the more than 300 000 lives taken as a killer tropical cyclone and storm surge ravaged the coast of Bangladesh with flood waters in 1970

watch- when a hurricane poses a direct threat to an area... typically 24-48 hours before the storm arrives... by the National Hurrican Center (Fl)... or by the Pacific Hurrican Center (Hawaii)

-warning- issued when it appears that the storm will strike an area

-accompanied by a probability

-these are issued for large coastal areas

-much area is "over warned"

-satellites

-buoys

-reconnaisance aircraft

-use ensemble forcasting for path prediction

-silver iodide seeding to reduce winds

-attempt to form multiple eyewalls

-do winds lower naturally had the storm not been seeded/ We Can't know...

-place oil on water to retard rate of evaporation

-the longer a storm survives, the more intense it can become

-with increased wind shear, precipitation is pushed downwind and does not cut off updraft

-an enormous thunderstorm that consists primarily of a single violent rotating updraft

-strong wind shear cause precipitation to not cut off

severe storms form because:

1)position of cold air above warm (unconditionally stable)

2)strong vertical wind shear

3)divergence caused by jetstream

-a line of thunderstorms, either right along a cold front or in the warm air 100 to 300 km out ahead of it

-'pre-frontal squall line thunderstorms' = largest and most severe squall line... may at times be supercells

****10.7

-Mesoscale Convective Complexes

-system where a number of individual thunderstorms grow in size and organize into a large and circular convective weather system

-occurs when conditions are favorable for convection

-long lasting and slow moving

-tend to form during summer and weak upper level winds

-a narrow zone where there is a sharp horizontal change in moisture... mostly observed in mid-west USA

-thunderstorms may form just east of these boundaries

-may be formed when warm, moist air rises along the forward edge of the gust front

-especially prevalent when the atmosphere is ver stable near base of thunderstorm

-**a dense arch-shaped ominous-looking cloud that often forms along the leading edge of a thundersotorm's gust front

-also called ARCUS CLOUD

-a surface boundary separating colder more-dense air from warmer less-dense air. Outflow boundaries form by the horizontal spreading of cool air that originates in a thunderstorm

-generally generated by multi-cell storms

-downdraft becomes so localized that it hits the ground and spreads horizontally in a radial burst of wind

  Microburst:

-downdraft with winds exceeding only 4km or less (exceeding 4 = macroburst)

-in spite of size, can be very powerful

-responsible for airplane crashes (associated with wind shear)

-mostly associated with severe thunderstorms, but not always?

**10.15

*10.16

-strong damaging straight line winds associated with a cluster of severe thunderstorms that most often form in evening or at night

-a line of thunderstorms on a radar screen that appears in shape of a bow

-bow echoes are often associated with damaging straightline winds and small tornadoes

-sudden warm downbursts

-originates high.... warms by compressional heating

-floods that rise rapidly with no advance warning

-sccours often when thunderstorms stall or move slowly

training- thunderstorms move quickly but pass over same area

-like a train on railroad tracks

-estimated 50 thousand occur each day in the world

-not found often in dry climates... more of an equatorial thing

-FLorida gets most... radiates less and less outwards (center = gulf coast)

-most hail found in central west area

-this is because enar florida it is too warm and near sea for hail and it melts before reaching the ground

-hail survives best when dry!! (evaporative cooling)

-discharge of energy (within cloud, from one to another, etc)

-can heat air to 30 000 C (5 X hotter than surface of the sun)

-thunder is the shock wave as air expands explosively

-can judge distance of lightning by approx 5 seconds per mile

sonic boom- occasionally mistaken for thunder

-produced when an aircraft exceeds sound speed

THEORY 1

-it occurs when graupel and hailstones fall through a region of supercooled droplets and ice crystals

-warm hail/cold droplets(positively charged)

**there is a net transfer of positive ions from warmer to cooler objects

-cold upper cloud becomes + charged , middle negatively charged, and low negative and mixed

THEORY 2

-particles are part negative and part positive charge

-during collision, larger particles become negatively charged, and smaller become positively charged, which are swept to top

-negative bottom of cloud causes positive charges to aggregate ont he ground... this region follows moving cloud

-positive charge most dense on protruding objects

-cloud-to-ground lightning begins within cloud when electrical potential gradient exceeds 3million volts

Stepped Leader - 

-each discharged covers approximately 50-100 meters, then stops for about 50 millionths of a second, then ocurs again

-usually invisible to human eye, as tip of leader approaches ground the potential gradient increases and current of positive charge leaves ground to meet it

Return stroke - what we see.... the current surges upward towards cloud once connected

Dar Leader - 

-the discharge of electrons that proceeds intermittently toward the ground along the same ionized channel taken by the initial lightning stroke

************

90% of lightning is NEGATIVE CLOUD TO GROUND LIGHTNING

10% of lightning is POSITIVE CLOUD TO GROUND LIGHTNING... (cloud is positive)

ribbon lightning- forms when wind moves ionized channel over

beak L - appears to break up (beaks on a chain)

Ball L -cause is enigma... mysterious ball floats around

Sheet L- flashes entire sky

Dry L- cloud to ground with no rain (starts fires)

Heat L - distant lightning seen by not heard... appears to be orange when far away

red sprite/blue jet - shoorts from top of cloud into upper atmosphere

-a bright electric discharge that is prejoected from objects (usually pointed) when tehy are in a strong electrical field

"corona discharge" - continous supply of sparks

-Use lightning direction finder, which works by detecting the radio waves produced by lightning

-lightning per year starts 10 k fires in USA and 50+ million dollars timber loss

-seeding cumulonimbus with hair this aluminum pieces (messes with charge)

-a rapidly rotating column of air that blows around a small area of intense low pressure with a circulation that reaches the ground

-sometimes called twisters or cyclones... variety of shapes and forms

funnel cloud - a tornado whose circulation has not reached the ground

-diameter of most between 100 and 600 meters... though ranges even more than this... one hit Nebraska with diameter of 4000m

-tend to move from the wouthwest towards the northeast

-dust-whirl stage - first step... light damage

then mature stage - damage is most severe... greatest width and most vertical

decay stage - finds the tornado stretched into the shape of a rope... becomes greatly contorted before it finally dissipates

USA gets most... average more than 1000 annually, and got 1819 in 2004

-have occurred in every state, though mostly tornado valley

-frequency highest during the spring and lowest during the winter (most march-july)

-most frequent in late afternoon

-strongest around 220 knots, and most tornadoes probably have winds of less than 125 knots

-when one is approaching from the southwest, its strongest winds are on its southeast side

suction vortices - smaller whirls within a tornado... mostly just within violent tornadoes

-only about 10 m in diameter, but they rotate very fast and apparently do a great deal of damage

watch - tornadoes are likely to form over the next few hours

-issued by storms prediction center in oklahoma

warning - issued by NWSO... some commmunities have sirens

-over the years, have had increase in tornadoes but deacrease in death

F0/F1 - weak tornadoes, and only very few each year go about F3 (violent), with perhaps one or two F5 reported annually.

-violent ones cause death

**as wind doubles, the force of the wind on the object increases by a factor of four

-tornadoes that form with supercell thunderstorms

-vortex tubes caused by wind shear are hit by a strong updraft of a thunderstorm, which tilts the tube

MESOCYCLONE - the rising rotating column on the sourth side of the storm, perhaps 5-10 kilometers across

-large hailstones usualy fall just north of the updraft

-bounded weak echo region

-region inside the thunderstorm where radar is unable to detect precipitation

-spiral around the mesocyclone... the rotating precipitation may on the radar screen, unveil itself in the shape of a hook

nonsupercell tornadoes- tornadoes that do not occur in association with a pre-existing wall cloud (or a mid-level mesocyclone)

-they may occur with intense multicell storms as well as with ordinary cell thunderstorms, even relatively weak ones

-some start at the cloud, some begin at the ground

gustnadoes - tornadoes that form along a gust front

-relatively weak tornadoes normally are short lived and rarely inflict significant damage

landspouts - rather weak, short lived tornadoes that occur with rapidly building cumulus congestus clouds

-these commonly form over east central colorado

-look like water spouts