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Weather Module 4 > Cyclonic Development > Flashcards

Cyclonic Development Flashcards

1
Q

We can get an idea of the instantaneous trend for a pressure center from the _______ in its vicinity.

A

Pressure tendency

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2
Q

List the 3 factors that affect the central value of a low

A

Topography
Diurnal pressure changes
Diabatic influences

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3
Q

Central pressure values are not always accurate in ________ regions

A

Mountainous

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4
Q

List the 6 factors which contribute to divergence and convergence in a developing low pressure system.

A 
Sensible heat transfer
Latent heat transfer
Surface vorticity
Horizontal thermal advection
Horizontal vorticity advection
Heat transfer by vertical motion
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5
Q

Maximum WAA and minimum CAA =

A

Divergence aloft

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6
Q

Maximum CAA and Minimum WAA =

A

Convergence aloft

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7
Q

Sinking air(compression) will contribute to:

A

Atmospheric Divergence

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8
Q

Areas of maximum heating will produce :

A

Divergence

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9
Q

Local heating due to latent heat release will contribute to:

A

Atmospheric divergence

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10
Q

In the free atmosphere, upper level divergence and low level convergence tends to ________ surface pressure

A

Lower

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11
Q

The atmosphere is said to be baroclinic when there is:

A

a horizontal temperature gradient on an isobaric surface

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12
Q

The strength of a baroclinic zone depends mainly on:

A

the thermal contrast or the temperature gradient

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13
Q

The thermal contrast is indicated by:

A

the number of isotherms in the baroclinic zone

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14
Q

List the 5 stages in the life cycle of a baroclinic depression:

A 
Formation
Development
Maturity
Occlusion
Dissipation
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15
Q

When contributing factors have comibned in such a way that their net effect is to generate surface vorticity, it is known as

A

Cyclogenesis

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16
Q

Some good indicators of the formation of a new low center are:

A
  • New vorticity center developing at 500 hpa
  • Intensification of vorticity and thickness advection over a center where there was none previously
  • A kink developing in a baroclinic zone
  • Awareness of favorable areas of cyclogenesis
  • Changing edges of mid level cloud
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17
Q

4 important points about formation are:

A
  • Baroclinic zone associated with a “leaf” of CI cloud
  • Cyclonic circulation is onset
  • A frontal wave crest forms along the baroclinic zone
  • An ill defined S appears along CI back edge
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18
Q

Most baroclinic lows which are developing are associated with:

A

A 500 hpa short wave trough located 3 to 5 degrees of longitude behind the low.

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19
Q

Surface lows are guided, in general, by the:

A

500 hpa flow

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20
Q

Development begins when the surface vorticity increases due to the production of:

A

Divergence aloft

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21
Q

When the lag between the thickness and contour patterns is about a quarter of a wavelength we have:

A

baroclinic instability

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22
Q

As the wave matures, The following features with the depression occur:

A
  • The low has deepened and intensified considerably
  • The wave amplitude has grown on the baroclinic zone
  • Isotherms are curved in the direction toward which the air is moving
  • The amplitude of the upper trough and ridge is increasing and will reach a peak at the end of this stage
  • East of the low WAA has increased considerably
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23
Q

The mature system has a ______ shape form

A

comma

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24
Q

the following dynamic features are to be noted:

A
  • The direction of motion is parallel to the isobars in the warm sector
  • The thermal wave is rotating counter clockwise about the center
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25
Q

What are 5 indicators that occlusion is occuring?

A
  • Deep Upper trof due to CAA
  • A few closed contours form the upper trof
  • Surface low loses thermal support
  • Cold air appears to undercut warm front
  • Cloud stretches along trowal/surface front
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26
Q

In the dissipation stage, due to friction and the static stability combined with cooling of the air column, _________ is increasing in both the boundary layer and the free atmosphere.

A

Convergence.

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27
Q

during the depression stage, the central pressure is _______ and the depression is ________

A

Rising, Filling

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28
Q

Indicators of dissipation are:

A
  • Surface low moves toward 500 hpa heights
  • The air column cools down and produces a cold low
  • Convergence increases in the whole air column
  • Central pressure usually rising
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29
Q

List the 5 methods that can be used to indicate the motion of a low pressure system

A
  • History
  • Isallobaric pattern
  • isobaric flow
  • baroclinic zone
  • 500hpa flow
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30
Q

With an extremely asymmetrical low pressure system, which way will the center tend to move?

A

Along the longest axis, with very little adjustment for the isallobaric field.

31
Q

With regards to the 500 hpa flow, what is the rule regarding pressure and movement?

A

6 Dam movement for every 8hpa change.

32
Q

A surface low will usually move in a direction which is:

A

parallel to the isobars in the warm sector

33
Q

if the baroclinic zone is relatively flat, the motion of the surface low will be:

A

parallel to the orientation of the isotherms or the thickness lines

34
Q

For the purposes of this course, summer severe weather will be taken as weather activity associated with ___________ only.

A

Strong convective activity

35
Q

what is the definition of severe winter weather?

A

Weather occurring in the winter which can have a significant effect on humans and the environment

36
Q

List the 4 thermodynamic factors favorable for the development of summer severe weather:

A

Warming in the lower levels
Cooling at the upper levels
Adding moisture in the low levels
Drying at upper levels

37
Q

to diagnose instability, one should look for:

A
  • Pools or troughs of cold air aloft
  • Pools or ridges of warm air in the low levels
  • Indications of lapse rates greater than the wet adiabatic lapse rates
38
Q

The 3 dynamic factors favourable for the development of summer sever weather are

A

Upper level divergence
Vertical wind shear
Low level convergence

39
Q

Statistics have shown that _________ correlates to severe summer weather.

A

strong vertical wind shear

40
Q

What are the 5 local effects of topography that aid in the formation of summer severe weather

A
  • Vegetation and water may provide moisture
  • Hilly terrain causes differential heating
  • Channeling can provide low level convergence
  • Sloping terrain can add lift
  • Roughness discontinuity can cause convergence
41
Q

What is the most destructive phenomena in north america?

A

Tornadoes

42
Q

When are tornadoes most frequent in Canada?

A

May and june, between 15h00 and 18h00 lcl

43
Q

tornadoes occur much more frequently with __________ thunderstorms associated with cold fronts and squall lines.

A

Supercell

44
Q

__________ is a signpost to tornadoes and violent turbulence.

A

Cumulonimbus mamma cloud

45
Q

List the 8 characteristics of a tornado:

A
  • Mesocyclone
  • Very intense wind vortex
  • small diameter
  • extends from cumulonimbus
  • irregular track
  • called waterspout over water
  • duration
  • accompanied by other thunderstorm phenomena
46
Q

Tornadoes often develop from supercells which contain:

A

Mesocyclones

47
Q

Most tornadoes have wind speeds between ______ and _______ but can attain speeds of _______

A

64km/h to 179km/h. 480km/h

48
Q

the average diameter of a tornado is ______ but can reach ________

A

10-100 meters, 1-2 km in diameter

49
Q

Although waterspouts are tornadoes by definition, they don’t count as such unless:

A

they hit land

50
Q

most tornadoes last less than:

A

10 minutes

51
Q

Who is the F scale named after?

A

Dr T. Fujita

52
Q

Define stability index:

A

An objective method for diagnosing the occurrence and severity of summer convective activity

53
Q

while stability indices are used for the quick assesment of severe weather potential, they also have limitations, such as:

A
  • they are not always portable between areas due to being regionally developed
  • they often do not take all factors into account
  • they may be based on forecast parameters
54
Q

List the 5 stability indices used in Canada

A
  • Lifted index (LI)
  • Showalter index (SI)
  • Totals-totals index (TT)
  • George index (K)
  • Sly index
55
Q

What is the Lifted index equation and significant value?

A
  • LI= T500hpa - T of Lifted parcel from surface to 500hpa

- Severe thunderstorm best at -2 or lower

56
Q

What is the showalter equation and significant value?

A
  • SI = T500hpa - T of parcel lifted from 850hpa to 500hpa

- severe thunderstorm best at -6 or lower

57
Q

What is the totals totals equation and significant value?

A

TT=VT+CT
VT= T850-T500
CT = Td850 - Td500
- 48 indicates severe thunderstorms, 55 indicates tornadoes possible

58
Q

the George or K index has proven useful in indicating the probability of________

A

Air mass thunderstorms

59
Q

What is the george equation and significant values

A 
K= (T850-T500) + Td850 - (T700 - Td700)
>40 = 100% chance of thunderstorms
60
Q

Where was the sly index developed and what is it an indicator of?

A

Alberta, CB development in the afternoon

61
Q

List the conditions that are categorized as severe winter weather

A 
Blizzards
Coldwave
Heavy Snowfall
Freezing rain
Strong wind
Heavy blowing snow
Freezing spray
Wind chill
Heavy Rain
Snow squalls
62
Q

A blizzard is officially defined as a storm with:

A

Vis less than 1 km in SN or BLSN
Wind greater than 40 km/h
Temperature less than -10
6 hours or more

63
Q

What is a cold wave distinguished by?

A

a rapid fall in temperature within a 24hr period

64
Q

How is heavy snow defined?

A

15cm or more accumulation in 24 hrs.

65
Q

Typically, where do larger accumulations of freezing rain occur?

A

Near and parallel to a stationary or slow moving frontal zone

66
Q

Heavy blowing snow is reported if the visibility is reduced to:

A

1/4 of a mile or less

67
Q

A snow squall is usually associated with:

A

lake effect snow or frontal snow

68
Q

List the 3 factors necessary for the formation of winter convective clouds (streamers)

A

Unstable temperature profile
Long Fetch
Little wind shear

69
Q

To ensure instability, _______ will be present below 1km

A

No inversion

70
Q

Organized bands of streamers can be expected if the shear is:

A

30 degrees or less below 3 km

71
Q

List the 5 characteristics of snow squalls

A 
Shallow systems
Inland penetration up to 200km
Narrow band of precip
Duration of several hours to days
Snowfall can be heavy
72
Q

Snow squall tops are generally less than:

A

10000ft

73
Q

What are the 3 lows over the rockies?

A

Alberta lows
Nebraska lows
Colorado lows

Weather Module 4 (4 decks)

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