Thunderstorms and tornadoes!
Why do we have thunderstorms?
- good way for atmosphere to release energy (when warm moist air meets colder drier air, the water vapor condenses and makes clouds. As the vapor condenses it releases heat, a form of energy. A large amount of the thunderstorm's energy comes from the condensation process forming the clouds) - helps the keep the Earth in electrical balance. Earth is neg while atm is positive. There is a steady flow of electrons into the atmosphere - lightning helps return this charge
The stages of thunderstorm life cycle.
1. Developing stage 2. Mature stage 3. Dissipating stage
What do storm spotters look for when trying to ID a tornado/dangerous storm?
1. Inflow bands (ragged bands of low cumulus clouds extending from the main storm - spiral nature indicates rotation) 2. Beaver's tail (smooth, flat cloud band that skirts around the Southern edge at precipitation area - rotation!) 3. Wall cloud (isolated cloud lowering attached to the rain-free base - usually exists for 10-20 minutes before a tornado appears) 4. Rain-free base (as the storm intensifies, the updraft draws in low-level air - the moisture from this air condenses below the rain-free base to form the wall cloud) 5. Rear-flank downdraft (dorwnward rush of air on the back side of the storm that descends with the tornado - looks like a clear slot, with curtains of rain wrapping around the cloud base circulation) 6. Condensation funnel (tornado)
What do you need to generate a tornado?
1. Instability (to create an environment capable of rapid rising motion) 2. A trigger (to initiate rising motion) 3. Wind shear (to create spin for speed necessary for a rotating thunderstorm/tornado)
Lifting triggers/mechanisms (need for class)
1. Lifting by a front. Cold front goes under, warm air goes on top - lots of rotation at the same time. 2. Lifting by a gust front from a thunderstorm - old thunderstorm cold air outflow lifts warm air to make another thunderstorm. 3. Lifting by a sea-breeze front (sometimes a sea breeze can act as a cold front to lift air near the coast.
What damage can thunderstorms cause?
1. Rainfall -> flash flooding 2. Lightning -> fires 3. Hail 4. Strong straight-line winds (Destruction!) 5. Tornadoes
How are thunderstorms formed?
1. Source of moisture (usually warm/moist oceanic air) 2. Conditionally unstable atmosphere 3. A trigger (anything that fosters the development of rising motion)
Techniques for tornado detection:
1. Storm spotters 2. Doppler radar 3. Hook echo 4. NWS radars (dual polarization radar)
What are some trigger mechanisms to bring an air parcel to the buoyancy level? (in depth, don't need to know this level)
1. forced uplift over mountains 2. localized regions of excess surface heating 3. fronts (boundaries between air masses with different thermal properties) 4. gust fronts (cold gusts from other thunderstorms) 5. Drylines (boundaries between air masses with different moisture contents) 1&2 = air mass thunderstorms (supercells)
What is a bow echo?
A radar signature of a squall line that bows out as winds fall behind the line and circulations develop on either end. Tornadoes can occur on the leading edge of a bow echo.
How do tornadoes originate from supercells?
A rotating updraft will lead to supercell development. Wind shear can cause this rotation (when winds at two different levels above the ground blow at different speeds/directions). Rising air within the thunderstorms tilts the rotating air, giving rotation.
What is a derecho?
A widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms.
Time of occurrence of tornadoes.
Between 4-9pm.
What do thunderstorms look like?
Can either look like tall heads of cauliflower or can have "anvil," a flattening off the top cloud layers. This nvil occurs when the updraft (warm air rising) has reached a point where the surrounding air is about the same temperature or even warmer.
What are some triggers for tornados/thunderstorms?
Cold or warm fronts dry lines gust fronts high terrains
What is conditional instability?
Conditionally unstable: instability is conditional upon air being uplifted to the LFC by some mechanism. Normally, air parcel is rising due to internal differences with the atmospheric conditions, but it will stop once these conditions equalize. Conditional instability occurs when some external lifting mechanism continues lifting the air to a point where it is above the condensation level. As the air continues to rise, it will eventually cool to the dew point temperature, the point at which the air is completely saturated with water vapor. Once this rising air parcel passes the environmental curve (or ELR), it becomes buoyant and self-sustaining. This level is called the Level of free convection. At this level, it can produce a thunderstorm.
What does convection have to do with thunderstorms?
Convection is the upward atmospheric motion that transports air (+ any moisture assoc. with it) usually due to surface heating.
What is a dryline?
Drylines are boundaries between air masses with different conditions. For example, the dry line along the coast of mexico, penetrating into Oklahoma. This line is the boundary for the dry air coming from over mexico and the moist air coming from the gulf.
Why do 85% of tornadoes occur in North America?
Have hot winds coming in from the South (warm + moist). These warm air masses can penetrate very far North. Maximized over the center of Oklahoma
Instability in terms of a thunderstorm?
If an air parcel is shifted from equilibrium, it will accelerate away from the original position. With thunderstorms, there is warm air at the surface and cold air in the atmosphere. Warming air from the afternoon sun facilitates lifting, while there is cold air in the atmosphere. This will lead to a warm parcel of air surrounded by cold atmosphere.
In order to get a thunderstorm, you have to go out on a "LIM"
L = lift I = instability M = moisture
Safety measures with tornadoes?
Listen to media. Move to shelter. Go to low elevation (if outside)
What is the difference between the following mesoscale convective systems (MCS): mesoscale convective complex (MCC) and a mesoscale convective vortex (MCV)?
MCS: a collection of thunderstorms that act as a system. MCC: a particular type of MCS that is a large, circular, long-lived cluster of showers and thunderstorms identified by satellites. MCV: A low-pressure center within an MCS that pulls wind into a circling pattern or vortex.
Describe the developing stage of a thunderstorm life cycle. (aka towering cumulus stage)
Marked by a cumulus cloud being pushed upward by a rising column of air (updraft). It will soon look like a tower. Does not typically produce tornadoes. Updrafts are usually suppressed by the weight of condensation. There is also no inherent rotation to work with (though this is overcome by wind shear)
Describe the dissipating stage of a thunderstorm life cycle.
Most likely time for hail, heavy rain, frequent lighting, strong wind, and tornadoes. Eventually a large amount of precipitation is produced and the updraft is overcome by the downdraft beginning the dissipating stage. Gust will move a long distance and cut off the warm moist air that was feeding the thunderstorm.
Types of thunderstorms?
Multi-cell storm (common, new updrafts form along the leading edge of rain-cooled air. Single-cell storm (small, brief, weak storms typically driven by heating on a summer afternoon) Squall line (group of storms arranged in a line) Supercell (long-lived and highly organized, feeding off an updraft, is tilted and rotating)
Why do tornadoes need wind shear?
Necessary to create a horizontal rolling column of air (high velocity) in the region of a supercell. It is tilted vertically by the updraft and can possibly become a tornado. The localized wind shear acts as the rotation for tornadoes (shear will tilt the storm diagonal, manifesting as rotation)
Can you ALWAYS see tornadoes?
No - it's just a column of wind. You can't see it unless it forms a condensation funnel (water, dust, debris)
Myths about tornadoes
Skyscrapers prevent tornadoes. Highways are a place of shelter. If condensation doesn't reach the ground, the tornado can't do damage. Tornadoes always move SW to NE.
What is the relationship between DALR (dry adiabatic lapse rate for air parcel) and the ELR (environmental lapse rate for the environment) in stable, neutral, and unstable conditions?
Stable: ELR < DALR (parcel cools faster then environment, becoming more dense and accelerates back to its original position) Neutral: ELR = DALR Unstable: ELR > DALR (air parcel is warmer and less dense than the surrounding environment, so it keeps rising (Accelerating away))
Why is it important to study tornadoes?
The majority of economic losses due to disasters are hurricanes and droughts - the extent of damage/death is a result of unpredictability of these storms and the crazy winds. Recently, they've become much more expensive (though less losses than other disasters because of the localization of tornadoes). Fatalities decreased due to better warning times.
An unstable air parcel needs to expand because it is so dense. How will this happen?
The parcel of air will rise and move into regions of low pressure and expand. This expansion will result in a decrease in kinetic energy so the temperature in the air parcel will cool. It will continue rising and expanding to a certain point, at which it is now at the same temp as the atmosphere and will no longer rise.
What is the dry adiabatic lapse rate? (this is the rate for the air parcel)
The rate at which dry air cools with an increase in altitude.
What is the moist adiabatic lapse rate?
The rate at which moist air cools with an increase in altitude.
What is the environmental lapse rate?
The rate at which temperature decreases with altitude in the stationary atmosphere.
What is the lapse rate?
This is the rate at which air temperature falls, with increasing elevation (deg/km). Lapse rate decreases by 6˚C for every kilometer in the layer between 2 and 3km (+6/1km). Defined to be positive when the temperature falls with increasing elevation. Lapse rate is 10˚C/1000km between 0 and 2000km. (10˚C/km)
What is the dew point temperature?
This is the temperature at which air can no longer hold water vapor, and vapor will condense into liquid water.
The Fujita scale
This scale goes by wind speeds. EF-0 (65-85mph), EF-1 ... EF-5 (<200mph). It is a damage scale that incorporates 28 different indicators (with 8 degrees of damage for each factor. 1 = beginning of visible damage, 8 = complete destruction)
How do tornadoes and hurricanes differ?
Triggers: they both need triggers Wind shear: bad for hurricanes but a key factor in thunderstorm/tornadoes. Winds: speeds of tornado winds are greater but the extent of hurricane winds is much larger Scale: Saffir-Simpson (hurricanes) vs. Fujita scale (tornadoes) Warning time: tornadoes (short) vs. hurricanes (large)
Weather radar vs. doppler radar?
Weather radar is images taken from satellites. Doppler radar uses frequency of a wave returning to calculate wind speed based off of its affect on precipitation.
How does instability occur?
When an air mass can't go back to its original equilibrium position in the absence of the changing force (like a ball on top of an upside-down bowl). Instead, the air parcel will accelerate away. This occurs due to warming at low levels or cooling at higher levels (or opposite, like with freezing rian).
Describe the mature stage of a thunderstorm life cycle.
When the updraft continues to feed the storm, but precipitation begins to fall, creating a downdraft. When this hits the ground, it will cause a gust front.
How do moving airmasses allow for supercell formation?
Winds tend to curve east due to the presence of the jet stream. Cold front going SE, Warm front going NE. Dry front coming from ~ Mexico. Dry front over Oklahoma.
What is a tornado?
a narrow, violently rotating column of air that extends from the base of a thunderstorm to the ground.
What is a supercell?
an often-dangerous thunderstorm with a very organized internal structure including a rotating updraft that allows it to keep going for up to several hours. Supercells are capable of producing severe weather including high winds, large hail, and strong tornadoes. They are most frequently isolated and often develop in the warm air ahead of a squall line. A supercell also usually forms in an environment with strong vertical wind shear that causes the updraft to begin rotating.
How does doppler radar work?
can be at a fixed or mobile site. It can measure the speed of wind b/c the beam that is received by the radar will have a different frequency depending on the motion of the water drops. Viewing angle is lifted upward to view winds at higher surface. Can measure wind velocity and reflectivity (intensity of precipitation)
Non-supercell tornadoes?
form from vertically spinning air-parcels occurring near the ground, caused by wind shear from warm, cold, or sea breeze front, of a dryline. Updraft will move over the spinning and stretch it, forming a tornado.
Why do tornadoes with smaller radius of rotation have faster wind speed?
r(wall) • v(wall) = r (tornado) • v(tornado) The smaller the radius of rotation, the faster with wind speeds
The most destructive and deadly tronadoes occur from...
supercells (mesocyclones)
Tornadoes form in association with...
the rotating supercell thunderstorms, often associated with a mid-latitude LPS.
What is the most common time that tornadoes occur?
very early in the season. There is a boundary that changes with the season due to the warm and cold air masses moving as the temperature warms. As the boundary migrates northward, will have higher incidence of tornado activity. (Early april - Georgia. Late june - Dakotas)
