Cyclonic Development Flashcards
We can get an idea of the instantaneous trend for a pressure center from the _______ in its vicinity.
Pressure tendency
List the 3 factors that affect the central value of a low
Topography
Diurnal pressure changes
Diabatic influences
Central pressure values are not always accurate in ________ regions
Mountainous
List the 6 factors which contribute to divergence and convergence in a developing low pressure system.
Sensible heat transfer Latent heat transfer Surface vorticity Horizontal thermal advection Horizontal vorticity advection Heat transfer by vertical motion
Maximum WAA and minimum CAA =
Divergence aloft
Maximum CAA and Minimum WAA =
Convergence aloft
Sinking air(compression) will contribute to:
Atmospheric Divergence
Areas of maximum heating will produce :
Divergence
Local heating due to latent heat release will contribute to:
Atmospheric divergence
In the free atmosphere, upper level divergence and low level convergence tends to ________ surface pressure
Lower
The atmosphere is said to be baroclinic when there is:
a horizontal temperature gradient on an isobaric surface
The strength of a baroclinic zone depends mainly on:
the thermal contrast or the temperature gradient
The thermal contrast is indicated by:
the number of isotherms in the baroclinic zone
List the 5 stages in the life cycle of a baroclinic depression:
Formation Development Maturity Occlusion Dissipation
When contributing factors have comibned in such a way that their net effect is to generate surface vorticity, it is known as
Cyclogenesis
Some good indicators of the formation of a new low center are:
- 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
4 important points about formation are:
- 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
Most baroclinic lows which are developing are associated with:
A 500 hpa short wave trough located 3 to 5 degrees of longitude behind the low.
Surface lows are guided, in general, by the:
500 hpa flow
Development begins when the surface vorticity increases due to the production of:
Divergence aloft
When the lag between the thickness and contour patterns is about a quarter of a wavelength we have:
baroclinic instability
As the wave matures, The following features with the depression occur:
- 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
The mature system has a ______ shape form
comma
the following dynamic features are to be noted:
- The direction of motion is parallel to the isobars in the warm sector
- The thermal wave is rotating counter clockwise about the center
What are 5 indicators that occlusion is occuring?
- 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
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.
Convergence.
during the depression stage, the central pressure is _______ and the depression is ________
Rising, Filling
Indicators of dissipation are:
- 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
List the 5 methods that can be used to indicate the motion of a low pressure system
- History
- Isallobaric pattern
- isobaric flow
- baroclinic zone
- 500hpa flow
With an extremely asymmetrical low pressure system, which way will the center tend to move?
Along the longest axis, with very little adjustment for the isallobaric field.
With regards to the 500 hpa flow, what is the rule regarding pressure and movement?
6 Dam movement for every 8hpa change.
A surface low will usually move in a direction which is:
parallel to the isobars in the warm sector
if the baroclinic zone is relatively flat, the motion of the surface low will be:
parallel to the orientation of the isotherms or the thickness lines
For the purposes of this course, summer severe weather will be taken as weather activity associated with ___________ only.
Strong convective activity
what is the definition of severe winter weather?
Weather occurring in the winter which can have a significant effect on humans and the environment
List the 4 thermodynamic factors favorable for the development of summer severe weather:
Warming in the lower levels
Cooling at the upper levels
Adding moisture in the low levels
Drying at upper levels
to diagnose instability, one should look for:
- 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
The 3 dynamic factors favourable for the development of summer sever weather are
Upper level divergence
Vertical wind shear
Low level convergence
Statistics have shown that _________ correlates to severe summer weather.
strong vertical wind shear
What are the 5 local effects of topography that aid in the formation of summer severe weather
- 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
What is the most destructive phenomena in north america?
Tornadoes
When are tornadoes most frequent in Canada?
May and june, between 15h00 and 18h00 lcl
tornadoes occur much more frequently with __________ thunderstorms associated with cold fronts and squall lines.
Supercell
__________ is a signpost to tornadoes and violent turbulence.
Cumulonimbus mamma cloud
List the 8 characteristics of a tornado:
- Mesocyclone
- Very intense wind vortex
- small diameter
- extends from cumulonimbus
- irregular track
- called waterspout over water
- duration
- accompanied by other thunderstorm phenomena
Tornadoes often develop from supercells which contain:
Mesocyclones
Most tornadoes have wind speeds between ______ and _______ but can attain speeds of _______
64km/h to 179km/h. 480km/h
the average diameter of a tornado is ______ but can reach ________
10-100 meters, 1-2 km in diameter
Although waterspouts are tornadoes by definition, they don’t count as such unless:
they hit land
most tornadoes last less than:
10 minutes
Who is the F scale named after?
Dr T. Fujita
Define stability index:
An objective method for diagnosing the occurrence and severity of summer convective activity
while stability indices are used for the quick assesment of severe weather potential, they also have limitations, such as:
- 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
List the 5 stability indices used in Canada
- Lifted index (LI)
- Showalter index (SI)
- Totals-totals index (TT)
- George index (K)
- Sly index
What is the Lifted index equation and significant value?
- LI= T500hpa - T of Lifted parcel from surface to 500hpa
- Severe thunderstorm best at -2 or lower
What is the showalter equation and significant value?
- SI = T500hpa - T of parcel lifted from 850hpa to 500hpa
- severe thunderstorm best at -6 or lower
What is the totals totals equation and significant value?
TT=VT+CT
VT= T850-T500
CT = Td850 - Td500
- 48 indicates severe thunderstorms, 55 indicates tornadoes possible
the George or K index has proven useful in indicating the probability of________
Air mass thunderstorms
What is the george equation and significant values
K= (T850-T500) + Td850 - (T700 - Td700) >40 = 100% chance of thunderstorms
Where was the sly index developed and what is it an indicator of?
Alberta, CB development in the afternoon
List the conditions that are categorized as severe winter weather
Blizzards Coldwave Heavy Snowfall Freezing rain Strong wind Heavy blowing snow Freezing spray Wind chill Heavy Rain Snow squalls
A blizzard is officially defined as a storm with:
Vis less than 1 km in SN or BLSN
Wind greater than 40 km/h
Temperature less than -10
6 hours or more
What is a cold wave distinguished by?
a rapid fall in temperature within a 24hr period
How is heavy snow defined?
15cm or more accumulation in 24 hrs.
Typically, where do larger accumulations of freezing rain occur?
Near and parallel to a stationary or slow moving frontal zone
Heavy blowing snow is reported if the visibility is reduced to:
1/4 of a mile or less
A snow squall is usually associated with:
lake effect snow or frontal snow
List the 3 factors necessary for the formation of winter convective clouds (streamers)
Unstable temperature profile
Long Fetch
Little wind shear
To ensure instability, _______ will be present below 1km
No inversion
Organized bands of streamers can be expected if the shear is:
30 degrees or less below 3 km
List the 5 characteristics of snow squalls
Shallow systems Inland penetration up to 200km Narrow band of precip Duration of several hours to days Snowfall can be heavy
Snow squall tops are generally less than:
10000ft
What are the 3 lows over the rockies?
Alberta lows
Nebraska lows
Colorado lows
