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EAS 202 > 6: Thunderstorms > Flashcards

6: Thunderstorms Flashcards

1
Q

What is a thunderstorm, lifecycle, what it consists of

A
  • Storm accompanied by thunder and lightning
  • Consists of one or more convective/thunderstorm cells
  • Life cycle of a cell lasts 20-40 minutes
  • Heigh of cell is roughly width of cell
  • Cell. moves with the steering level winds
  • A supercell thunderstorm consists of one extremely strong cell
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2
Q

Single Cell Thunderstorm and Stages

A
  • A thunderstorm cell consists of a single updraft and downdraft
  • Each cell passes through a life cycle: cumulus stage, mature stage, dissipating stage
  • Simple thunderstorms consists of a single cell but more complex thunderstorms have numerous cells
  • Updraft: convection
  • Downdraft: precipitation falling to ground
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3
Q

Single Cell Thunderstorm Cumulus Stage/Developing Stage

A
  • Rapidly rising cumulus tower with cauliflower appearance
  • No downdraft
  • Precipitation process underway in cloud but no precipitation at ground
  • Updraft = moist air ascends and pressure falls due to gap created, causing expansion of air
  • Expansion causes cooling –> causes condensation –> causes release of latent heat –> causes temperature increase
  • In cloud air is warmer than ambient outside air, which causes updraft buoyancy –> causes upward acceleration due to higher temperature gradient –> causes enhanced updraft
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4
Q

Single Cell Thunderstorm Mature Stage

A
  • Begins when precipitation reaches surface
  • Updraft reaches tropopause, which it cant penetrate, so it spreayds out latereally, creating a symmetric anvil and overshooting top
  • Precipitation drag and evaporation produce downdraft
  • Downdraft spreads out at ground producing a gust front
  • Anvil cloud is ice and points in the wind direction
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5
Q

Single Cell Thunderstorm Dissipating Stage

A
  • Downdraft outflows cuts off supply of warm, moist air to updraft
  • Updraft dissipates and downdraft spreads throughout the cell
  • Lower part of cloud disappears and lateral anvil leaves
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6
Q

Thunderstorm Recipe

A

4 Ingredients
1. Convective instability: such as heavy air lies on top of light air (ex: ELR > DALR, with warm air below and cold air on top)
2. Sufficient humidity: fuel for explosion
3. Trigger in terms of surface convergence to release the loaded gun instability (break capping lid)
4. Wind shear that organizes the convection and extends the lifetime

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7
Q

What is Wind Shear

A
  • Vertical wind shear is the variation of wind speed/and or direction with height
  • Wind speed and direction can be found on the right side of skew-T log-P diagram
  • A curve that connects the end points of the wind vector plotted in polar coordinates is called hodograph
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8
Q

What is a hodograph

A

represents change in wind speed and direction with height
* image 6

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9
Q

Classification of Storms (by insurance company)

A
  • Wind storms
  • Rainstorms
  • Snowstorms
  • Hailstorms
  • Rotating storms
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10
Q

Thunderstorm Classification and what are they

A
  • Single cell storm: last about 30 minutes
  • Multicell cluster storm: group of cells moving as a single unit, with each cell in a different stage of its life cycle. Can produce moderate size hail, flash floods, and weak tornadoes
  • Squall line storm: consists of al ine of cells with a continues, well developed gust front the leading edge of the line. Can produce small to moderate size hail. occasial flash floods, and weak tornadoes
  • Mesoscale convective complex (MCC) storm: large cluster of many intereacting cells. Life time is 12-24 hours. Slow movers but widespread and subsantial rainfall
  • Supercells: defined as thunderstorm with a rotating updraft, these storms can produce strong downbursts, large hail, occasional flash floods and wek to violent tornadoes
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11
Q

Hodograph Storm Types

A

A. Little Shear: single cell
B. Linear Shear: multi cell
C. Directional Shear: supercell

image 7

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12
Q

Single Cell Storm Characteristics

A
  • Forms in environment characterzed by large conditional instability and weak vertical wind shear
  • Vertically erect for self destruction mechanism
  • Life cycle around 30 minutes
  • Driven mostly by convective instability
  • Sometimes called air mass storms because they form within air masses with horizontal homogeneity
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13
Q

Skew T Graphs Levels

A
  • In order for convection to happen you have to break the capping lid: mountains or convergence of two air masses
    1. Lifting Condensation Level (LCL): level where condensation begins, past saturation point
    2. Level of Free Convection (LFC): level at which the parcel is warmer than the environment so it freely rises
    3. Equilibrium Level (EL): level at which the parcels’ temperature becomes the same as the environment again

image 8

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14
Q

Multicell Storms

A
  • Individual cells follow steering level winds
  • Cells dissipate at the left flank and new cells are formed at right flank
  • Multicell storms as a whole move in a different direction than the individual cells
  • image 9
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15
Q

Life Cycle of Multicell Storm

A

As cell 1 dissipates, cell 2 matures and becomes briefly dominant. cell 2 drops heavy precipitation as cell 3 strengthens, and cycle repeates.

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16
Q

What is a gust front

A

Line of strong gust wind at line’s leading edge

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17
Q

Upslope East Winds

A

Storms on the east side of the Rockies set up by synoptic high and low pressure systems

18
Q

How do thunderstorms form in Florida

A
  • Due to colliding sea breezes
  • during the day, the land surface heats faster than ocean water surface
  • a sea breeze develops on both coastlines and they collide, cuasing horizontal convergence of air
  • Lifting causes deep convection (thunderstorms
  • image 10
19
Q

Warnings for Thunderstorm

A
  • Thunderstorm wathes
  • Tornado watches
  • no explicit lightning warnings
20
Q

Ideal Conditions for Severe Thunderstorms

A
  • Low with warm and cold fronts
  • Storm forms where moist warm low level jet (LLJ) crosses the high level tropospheric jet in warm sector
  • Dryline (western boundary of humid tongue = moisture front) triggers severe convection
  • cP from NW pushing behind cold front
  • Within warm sector there is cT and mT (in front of cold front and behind warm front) from Gulf of Mexico that can penetrate all the way to Alberta–> cT (warm but dry) and mT (warm and humid) so
  • Dry line: border between cT and mT: thunderstorm development occurs around this line
  • image 11
21
Q

Capping Lid and Severe Thunderstorms

A
  • Temperature inversion puts a lid between hot humid near surface air and air flow aloft
  • The lid allows for build up of convective instability (surface heating and upper level cooling)
22
Q

Dryline Identification

A
  • a narrow zone across which a sharp surface dewpoint gradient exists
  • image 12 –> thunderstorm is marked by a cross
23
Q

Characteristics of Supercell Thunderstorms

A
  • Long lived
  • Large spatial extent
  • Strong updrafts
  • Rotation fo a mescycle
  • Can lead to tornadoes
  • All thundersetorms require an initial lift of air
  • In the mature stage, contains both updraft and downdraft
  • Formation of cold pool
23
Q

What is a Microburst and what does it affect

A
  • Cold downdraft and large amount of waiter hits urface and will have a strong rebound, resulting in a secondary thunderstorm (microburst)
  • Headwind slows and lifts plane above normal path, while pilot compensates by dipping nose, plane enters downdraft and reduces plane’s lift
23
Q

Miroburst evolution

A
  1. Contact Stage: downdraft reaches surface
  2. Outburst Stage: produces extreme wind where it spreads
  3. Cushion Stage: downdraft cant penetrate surface due to dense cold pool
  • image 13
24
Q

How to determine if storms are short or long lived

A
  • Long lived convective system: strong winds going rowards the gust contains source of moisture
  • short lived convective system: downdraft overtakes updraft so moisture source is cut off
25
Q

What is a mesocyclone

A
  • rotating updraft in the counterclockwise direction (low pressure)
  • low level wind shear creates vorticity –> this rotation getes tilted into the vertical by the updraft
  • Strong wind shear and can extend to surface
26
Q
  1. The mature stage of the life cycle of a thunderstorm cell is characterized by
    a. updrafts only.
    b. both updrafts and downdrafts.
    c. cloud dissipation.
    d. downdrafts only.
    e. no updrafts and no downdrafts
A

b

27
Q

3.. The anvil top of a thunderstorm cloud is likely to be a ______ cloud that is composed of
______.
a. warm…………….supercooled water droplets
b. cold……………liquid water droplets
c. cirrus……………ice crystals
d. altocumulus……………water droplets
e. stratus……………drizzle

A

c

28
Q

4.. A gust front is associated with a(n)
a. intense thunderstorm.
b. land breeze.
c. chinook wind.
d. sea breeze.
e. None of these is correct

A

a

29
Q
  1. Appearance of a flat anvil top indicates that the developing thunderstorm cloud
    (cumulonimbus) has reached a(n) ______ portion of the atmosphere.
    a. unstable
    b. neutral
    c. conditionally stable
    d. humid
    e. extremely stable
A

e

30
Q

7.. A mesoscale convective complex (MCC)
a. is the same as a supercell thunderstorm.
b. consists of numerous interacting thunderstorm cells.
c. is usually located just ahead of a fast-moving, well-defined cold front.
d. has a life expectancy of less than an hour.
e. is most likely to occur in the Pacific Northwest.

A

b

31
Q
  1. A squall line usually forms
    a. along a stationary front.
    b. in the cold air mass well behind a cold front.
    c. in the mT air along or ahead of a cold front.
    d. in the fog and cold air mass just north of a warm front.
    e. None of these is correct.
A

c

32
Q
  1. Thunderstorm development is favored
    a. by stable air.
    b. over relatively cold surfaces.
    c. by free convection alone.
    d. by conditionally unstable maritime tropical air.
    e. in arctic air.
A

d

33
Q
  1. Thunderstorm cells associated with a fast-moving, well-defined cold front
    a. may be severe.
    b. often occur as a squall line parallel to and ahead of the front.
    c. often form an elongated cluster parallel to the front.
    d. All of the above are correct.
    e. None of the above is correct.
A

d

34
Q
  1. Thunderstorm development is triggered by
    a. uplift along a well-defined cold front.
    b. converging surface winds.
    c. uplift of warm, humid air along mountain slopes.
    d. forced convection.
    e. Any of the above is correct
A

e

35
Q
  1. A feature sometimes present in thunderstorms that may prolong the mature stage is (are)
    _____.
    a. abundant ice nuclei at high altitudes.
    b. an anvil top.
    c. a cold downdraft.
    d. precipitation.
    e. a tilted updraft.
A

e

36
Q
  1. A supercell thunderstorm is most likely to develop in the ______ sector of a mature extra-
    tropical cyclone.
    a. northwest
    b. southeast
    c. northeast
    d. southwest
    e. cold
A

b

37
Q
  1. A severe thunderstorm cell may be accompanied by__________.
    a. damaging surface winds.
    b. hail.
    c. heavy rainfall.
    d. frequent lightning.
    e. Any of these is correct
A

e

38
Q
  1. A dry line ______.
    a. is a likely site for development of a severe thunderstorm cell.
    b. separates hot, dry air from warm, humid air.
    c. often occurs over Texas and Oklahoma.
    d. All of the above are correct.
    e. None of the above is correct.
A

d

EAS 202 (14 decks)

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