Exam 3 Study Guide Flashcards
Does the sierra Nevada mountains have more snow typically than the rest?
Yes
What is an upslope storm?
Snow storm along the rocky Mountains caused by air flowing westward (to the west)
What characteristics of mountains influence snowfall?
Location (Near ocean), Height, Steepness
What is an atmospheric River?
Narrow flow of moist air in the lower and middle troposphere.
What does Atmospheric Rivers look like on satellite?
Long stream of clouds, or high water vapor concentration.
What is orographic lifting?
Forced ascent air that occurs on the windward (upslope) side of the mountains.
Would more snow be expected to fall on the windward or leeward side of a mountain range?
Windward side
Why does more snow happen on the windward side of the mountain?
Air rises on the windward side of a mountain, creating clouds and precipitation. Air sinks on the leeward side, warming and drying air.
What is the melting point?
Defines the freezing/melting point of water.
What type of precipitation would happen above and below the melting point?
Above - Snow
Below - Rain
What is a rain shadow?
A region that experiences little precipitation because it is located on the leeward slope of a mountain range.
Where are rain shadows located?
Leeward side of the mountain.
Where would the ideal locations be for low-pressure system and high-pressure system for heavy storm on the east slope of Colorado’s Front Range?
High-pressure north of colorado
and Low in south west corder of colorado
What general location is the surface wind blowing during an upslope storm in eastern colorado?
Easterly (Northeast, East, or southeast)
What surface wind direction factors heavy snowfall in Denver, colorado?
Northeast
What maximum speeds can downslope windstorms attain?
Gusts may exceed 100 knots (115mph)
What three factors determine the temperature of chinook winds?
- Temperature of air upstream of the mountains?
- Latent heat release in the clouds upstream
- Adiabatic Warming during descent.
Why is the dewpoint temperature typically lower on the leeward side of a mountain compared to the windward side during a downslope windstorm?
Precipitation falls out of the cloud on the windward side of the mountains. The dewpoint lowers when the temp hits it.
What three factors are common to weather patterns that produce Chinook winds?
- Stable layer upstream of a mountain a Kilometer or two above the mountaintop.
- Strong surface pressure gradient across the mountain
- Levels near mountaintop, background flow that is strong and from west.
Where do Santa Ana winds occur?
Southern California
How do Santa Ana winds differ from chinook winds near boulder?
- Santa Annas are
- more frequent
- Less intense
- Winds from east
Why are Katabatic winds most common in Greenland and Antartica?
Katabatic winds require high altitude, large ice sheets - which are present in Greenland and Antartica.
What is the difference between Foehn and Bora?
- Foehn - Warm downslope windstorm
- Bora - Cold Downslope windstorm
What is a lee wave?
A wave in airflow that forms as air passes over the mountain to the lee side.
Why is an inversion important in creating strong downslope winds?
As rising air encounters the inversion, it is forced to accelerate and move downslope, leading to the hydraulic jump.
What role does latent heat release play in the temperature experienced on the plains east of the Rockies during a chinook?
If precipitation falls out of clouds on the windward side, the moisture content is lower and air descending the leeward side will be warmer than air at the same altitude on the windward side.
How does a Katabatic Windstorm Develop?
When cold air sits atop an elevated ice sheet for day or more, and spills over the edge and accelerated by gravitation.
A Katabatic wind is a downslope winds. Explain why it is cold wind spite of warming due to adiabatic compression during decent.
Given that it is initially extremely cold, it does not warm up enough to be considered a warm wind.
How does the National Weather Service determine if a thunderstorm is sever?
It must meet at least one of the following criteria:
- hail with diameter 3/4 inch or larger,
- wind damage or gusts over 50 kts
- Tornado
Why is wind shear important to a sever thunderstorm?
Vertical wind shear separates the updraft and downdraft, preventing precipitation from falling into the updraft; Also makes rotation in thunderstorm
When would you expect airmass thunderstorms to form?
During afternoon
Where would you expect airmass thunderstorms to form?
Far from frontal boundaries, in the middle of an airmass.
Why are MCSs important to the Central Plains?
They provide summer rainfall, which is important for agriculture.
What type of sever weather is most common with MCSs?
Straight - line winds
Along what type of fronts do frontal squall lines typically form?
Surface cold fronts, dry lines or along upper level fronts.
During what time of year are frontal squall lines most common?
Cool season (mostly Spring)
What is a supercell thunderstorm?
Supercells are large ROTATING thunderstorms.
What type of sever weather do super-cells produce?
- Large Hail
- Strong Straight line winds
- Strong Tornadoes
What are boundary intersections?
The locations where two boundaries (fronts) meet.
What role do Boundary Intersection play in super-cells?
Supercells have a tendency to develop at these points of intersection.
List the four necessary elements for severe thunderstorm formation
- Source of moisture
- Conditionally unstable
- Trigger Mechanism
- Vertical Wind shear
What three ways in which severe thunderstorms typically organize?
- mesoscale convective systems –Frontal squall lines
- super-cells.
What two mechanisms lead to the formation of downdrafts in thunderstorms?
- Drag by precipitation
- Cooling by evaporation of falling precipitation
What time of the year are mesoscale convective systems most common?
Mid-Summer (Warm Season)
What causes the development of a mesoscale convective vortex in the last stages of an MCS?
The latent heat released during condensation process leads to a weak low pressure region at mid-levels, causing the clouds to rotate.
How would you identify a frontal squall line on an infrared satellite image?
Identify the comma cloud; the squall line is the line of clouds in the tail.
Why would a high CAPE environment be favorable for severe or even supercell storm formation?
CAPE is a measure of the rising air parcels positive buoyancy (speed). Large values mean conditions are favorable for deep cloud formation, and strong winds.
What is a mesocyclone?
It is the rotating updraft of a supercell.
What sequence of precipitation types would you experience if the core of the supercell were approaching you?
Virga, Light Rain, Moderate rain, Heavy rain, small hail, large hail
Rank the four types of thunderstorms by size, Largest to smallest
Frontal Squall line, MCS, Supercell, Airmass thunderstorm
How does the shape of the anvil of a severe thunderstorm differ from the shape of an airmass thunderstorm anvil?
An airmass thunderstorm anvil is typically much more symmetric than the anvil of a severe thunderstorm.
What environmental condition is required for supercell thunderstorms to acquire rotation?
Vertical Wind Shear
What is a mesocyclone?
A rotating updraft of a supercell thunderstorm. Normally near the region where the tornados are from.
How does a tornado family develop?
Multiple tornados emerging from a single supercell over time constitute a tornado family.
What is the characteristic signature of a tornado thunderstorm in a radar reflectivity image?
The hook Echo in a supercell. This is the free rain zone.
What process concentrates the rotation in a supercell thunderstorm?
Stretching
What is the role of low-level shear in the formation of tornadic supercells?
The horizontal rotation associated with low level vertical wind shear is tilted into the vertical by storm updraft, causing the storm to rotate.
What is vortex stretching?
Vortex stretching is a process where a column of rotating air is enlongated so that the radius of the vortex is decreased and the rotation velocity of the air is increased.
What is the physical principle used to explain vortex stretching?
Conservation of angular momentum
Where does a tornado form relative to the primary features of a supercell thunderstorm?
Typically forms on the southwest side of the storm under the rotating mesocyclone.
How do suction vortices form in a tornado?
In the process of vortex breakdown, a downdraft extends downward to the surface in the center of the tornado. Shear between outward flowing air from the base of the downdraft and inward flowing air drawn into the updraft generates rotation, which is stretched from suction cortices.
What is the typical ratio of the diameters of a mesocyclone and a tornado?
Mesocyclone - 5KM
Tornado - 500m
About 10/1
What months of the year are tornados most common?
Spring (Late April, May and early June)
why is the spring time most common for tornados?
- Airmass temp contrasts are large
- Low level sheer ahead of frontal boundaries.
- Large conditional instability
- Upper level jet streams are still strong.
What time of day are tornados most common?
Late afternoon into early evening.
When can it be difficult to assign an EF-scale rating to a tornado?
If a violent tornado strikes no structures, there is no basis to assign it a high EF-Scale rating.
Do all tornadic thunderstorms borne in supercells produce hook echoes in the radar reflectivity field?
No. In supercells, sometimes the rear flank downdraft has no precipitation within it and does no produce a radar echo.
Why is supercooled water important to the formation of hail in a thunderstorm?
Hail forms as supercooled water droplets accrete (collect) on falling ice particles without supercooled water there could be no hail.
At what altitudes in a thunderstorm does hail growth normally occur?
The freezing level typically can be found about 3km (2 miles) above the ground.
What is a hail embryo?
A small ice particle that forms the core of a hailstone.
Where is the hail embryo curtain in a supercell thunderstorm?
Along the main updraft, near the rear flank.
What trajectories do hailstones typically follow between the hail embryo curtain and the ground?
Float in the updraft, and fall in the foward flank of the updraft.
Where is large hail generally found on the ground relative to a thunderstorms strongest updraft?
On the northeast side of the updraft, close to the edge of the updraft.
What is the difference between dry and wet growth regimes of hail?
dry growth - when water freezes rapidly on the surface
Wet growth - When the water freezes slowly
Why does the National Weather Service not issue hail-specific warnings?
Where is no way of detecting hail with the current Doppler Radar system, unless the hail is really big.
What advantage will polarization radar give to forecasters in the future?
Polarization Radars, determine where the hail is falling with greater certainty.
Where is the United States does large hail occur most frequently?
- Northern Texas
- Oklahoma
What are the two broad types of damage caused by hail?
Damage to agriculture and damage to property each are about 1.5 dollars
How is hail damage related to horizontal wind speed?
Hail is greater with stronger winds because. The velocity is faster, and they can go sideways, so they can bash into windows.
How can hail storms grow?
Hail can grow to the size of softballs and grapefruits
Why are direct measurements of hail difficult to obtain?
Too dangerous to fly into hail storm, and Radar is not accurate.
Differentiate between the hail embryo and a hailstone.
A hail embryo is a small ice particle that serves as the core of a hailstone.
If you experience large hail during a thunderstorm, has the threat of a tornado passed?
No, The threat of a tornado is very near, since the large hail is close to the rain free base and the wall cloud.
Why is an overshooting top often a sign that a thunderstorm contains hail?
The overshooting top is a sign of a strong updraft, which can support large hail.
