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C School > Convective Severe > Flashcards

Convective Severe Flashcards

1
Q

Thunderstorm Regions

A

Continental Divide to the Appalachian mountains
“Tornado Alley” is has the highest tornado activity
March - June: Most tornados
March - Sep: More severe storms
This time frame is aligned with movement of the PFJ

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2
Q

Heavy Rain regions

A

Summer - SE

Winter - W Coast

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3
Q

Flash Flood

A

Most common Apr - Sep (July)
During afternoon/evening with max heating
Arid environments can flood more easily due to lack of moisture in the soil

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4
Q

Buoyancy (four stages)

A

Stage one: parcel achieves equilibrium
Stage two: Moves past equilibrium and rises (updraft/anvil)
Stage three: Precipitation drag & dry air entrainment (3-5km) creates downdraft
Stage four: Cold pool at SFC (evap cooling/dry air entrainment), neg buoyancy

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5
Q

CAPE

A

Temperature difference between ascent path and environment (Positive buoyancy)
Often in the range of 1000-2000L/kg

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6
Q

Cold Pool Strength

A

Deeper the pool + stronger the temperature difference = Increased winds

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7
Q

Downbursts

A

Very strong concentrated downdraft at least 40kts

Occur at the edge of a gust front

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8
Q

Microburst (general)

A

Dangerous small scale down bursts (.2nm-2.4nm)
Winds equal to F3 tornado
Can change in velocity of 50kts+

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9
Q

Wet Microbursts

A

“High reflectivity” microbursts
Convection develops in a surface based moist layer with dry air aloft
Mixing from these two layers along with precipitation drag create burst

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10
Q

Dry Microburst

A

“Low reflectivity” microbursts
Forms above a deep surface based dry layer
Precipitation falls and evaporates before reaching the ground
Downward acceleration will continue as long as the descending air is cooler than the surrounding environment

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11
Q

Hybrid Microburst

A

Changes from wet to dry or dry to wet

Hail and grapple are possible with strong winds

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12
Q

Type 1 Air Mass

A

Great Plains - Loaded Gun
Unstable sounding with an inversion that acts as a lid
Low level heating, mechanical lift and evap cooling can break the inversion
Severe storms

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13
Q

Type 2 Air Mass

A

Gulf coast (SE)
>80F and winds that decrease with height
Good thunderstorm producer but marginal severe weather producer

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14
Q

Type 3 Air Mass

A 
Pacific Coast (Cold core)
Cool mP in low levels 
SFC heating or warm waters that cause warming (COW)
Hail producer due to low freezing level
Lower levels of 50-70F and RH >70%
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15
Q

Type 4 Air Mass

A

Inverted V (desert regions)
Downbursts and virga
High wind producer

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16
Q

Type A synoptic

A

Dry Line (convergence along dry line)
>10F difference at line, 55F isodrosotherm
Moves faster than expected
Hail, winds and tornado threat
Most severe at bulges and during max heating

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17
Q

Type B synoptic

A

Frontal
Along or ahead of a cold front
Major tornado outbreaks
Max heating

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18
Q

Type C synoptic

A

Overrunning
Density based
Low level jet intersects warm/stationary front
Max intensity during max heating
Hail very common, tornados not common unless dew point reaches 14C/50F

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19
Q

Type D synoptic

A

Cold core
Cold core aloft/ Cool mP in low levels
Well defined cold core low or cut off low
Hail common but Tornados are seldom
Threat area is in the zone of intense low level wind ahead of dry intrusion
Max threat at max heating

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20
Q

Type E synoptic

A

Squall Line
Mature occluded system and low level jet
Threat area N of warm front and most intense at max heating
Usually in connection with overrunning and frontal

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21
Q

Mesoscale Convective System (MCS)

A

> 100km
May evolve from one cell or a small group of cells
Significant precipitation in eastern US

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22
Q

Squall Line

A

Usually created from an outflow boundary
> wind shear, > magnitude of shear, > CAPE = > severity
Weaker- narrow line // Stronger- comma appearance (2-4hrs)
Capped on each side with line ends
More severe weather on S portion // stratus and precipitation on N side
H’er pressure within the N cyclonic flow
If the squall line is stronger the comma may be distorted and is referred as MCV
Propagation driven by the speed of the cold pool
Usually follows the fronts/winds, if smaller than may move at an angle (bend)

23
Q

Squall lines in the tropics

A

Taller, slower, weaker, symmetric and moves from E to W

24
Q

Bow Echos

A

10-65nm long
Associated with severe winds
Form into a bow shape and transition to a comma shape
The core of the bow is the “rear inflow jet”
The smaller the echo the stronger the winds
Severe: -8 LI, CAPE >2500, 700mb winds 33kts (shear in lowest 2-3km)
Stronger the RIJ, > winds, > temperature difference

25
Q

Derecho

A

> 50kts and 250nm
3 reports of F1 damage OR 65kts/40nm with no more than 3 hrs in b/w
Progressive: single
Serial: multiple

26
Q

Mesoscale Convective Complexes (MCC)

A

~320nm, 6-12hrs
(-32C/100,000) (-52C/50,000)
Mostly nocturnal
700-500mb determines speed of MCC

  1. Genesis
  2. Development
  3. Mature
  4. Dissipating
27
Q

Cumulus stage (TS)

A

Base at CCL
Updraft only
Lose top
Radar echo forms

28
Q

Mature stage (TS)

A

Up and downdrafts
Max vertical extent
Anvil top
Heavy rain (virga)
Cold pool 3000-3500ft deep
Downdraft (precipitation drag, dry air entrainment/evap cool)
Hail at freezing level and wet bulb freezing level

29
Q

Dissipating stage (TS)

A

Only downdraft (inflow of warm, moist air is cut off)
Drizzle and light rain - recipitation ceases
Winds weaken
Lightning is still a hazard
“Orphan anvil” cloud

30
Q

Convective Ingredients

A

Instability: heating, moisture or vertical motion
Moisture: depth or near sfc moisture layer
Lift: synoptic- cannot act alone / mesoscale- can initiate alone
Exhaust: severe TS requires an exhaust (ULD)

31
Q

Holographs (segment, bulk and total)

A

Shear segment: magnitude between two levels
Bulk shear: magnitude between two levels w/out the in between
Total shear: net length where all segments are added together

32
Q

Wind shear speeds

A

Ordinary: ~20kts
Multi-cells: ~35kts
Supercells: ~50kts

33
Q

Single cell TS

A

Zig zag (disorganized)
30-60min
One updraft
Tornados rare but high winds and hail are possible
Highly dependent on instability
“Pulse” storm is common (short lived nature)

34
Q

Multi-cell TS

A

Modestly organized made up of a succession of single cell storms
Mod low level shear (30kts in lowest 2-3km)
Each cell has cold outflow boundary where new cells develop every 5-15 min
Straight line hodograph
More severe weather threat, hail >3/4th, tornado risk and flash flooding

35
Q

Supercell TS

A

Long-lived or persistent core with a rotating updraft
Hooked hodograph
Large hail, strong winds and tornadoes

36
Q

Mesocyclone

A

Rotating vortex with an updraft in a super cell storm
Develop with a tilted environment and/or horizontal wind shear
1-5nm diameter
50-150kts

37
Q

Weak Echo Region (WER)

A

At the mid levels an echo overhang to the “south” of the precipitation region
Good indication of a potentially severe storm

38
Q

Bounded Weak Echo Reigon (BWER)

A

Even stronger updraft where the overhang hooks further over and creates a “cavity” in the mid levels
Can produce large hail >2”

39
Q

Hook echo (pendant echo)

A

Mesocyclone eventually becomes so strong it wraps around the updraft within the storm (precipitation wraps also)

40
Q

V-notch

A

Mid and upper levels are blocked by the intense updraft

41
Q

Forward flank downdraft (FFD)

A

Cool and moist air that goes to the SFC and spreads (towards PBL winds)

42
Q

Rear flank downdraft (RFD)

A

Warm and dry (adiabatic)

Behind the storm

43
Q

Flanking line

A

Leading edge of RFD

44
Q

Wall cloud

A

Lowering of cloud base below supercell storm

Appears as a lowering of the updraft

45
Q

Tail cloud

A

Right of wall cloud (FFD)

46
Q

Heavy rain and hail

A

Main updraft or hook echo

47
Q

Tornados

A

Where RFD joint the FFD w/in the hook echo

48
Q

Classic supercell

A

Wedge shaped, hook echo, WER/BWER and inflow notch

49
Q

High precipitation supercell

A

Kidney bean shaped
Larger system due to moisture
Extensive hail, tornadoes, downburst and flash flooding

50
Q

Low precipitation supercell

A

Smaller due to lack of moisture
Rain is still possible
Less chance of a tornado

51
Q

Shallow supercell

A

Much smaller both horizontally and vertically than other supercell types
Occur with a hurricane falling inland or wintertime high shear low buoyancy situations
~2000ft tall and 3nm in diameter
Forecasting challenge due to size
Tornado potential

52
Q

Supercell environment

A

CAPE values of 1000-2000J/kg
~50kts in lowest 20,000AGL
Either severe wind shear or high CAPE values alone can great a severe storm

53
Q

Supercell formation

A

When the vertical wind profile is sheared, horizontal vorticity is present in the environment
The shear and buoyancy gradients across the cloud cause tilt
Stronger the shear, stronger the updraft and less tilt
Precipitation falls down the shear of the updraft
Updraft and low level horizontal vorticity create a mid level vortex couplet

54
Q

Supercell dissipation

A

Cold pool cuts off unstable air
Unfavorable environment (moisture decrease, stability, mnts etc)
OR collides w/ other convective storms

C School (3 decks)

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