ATMS 120 Exam 3

How do mesocyclones, wall clouds, and tornadoes relate to each other?

* Know sizes (biggest to smallest) 1) MEsocyclone 2) Wall cloud 3) torando

What is a shelf cloud? How does it form and what weather conditions might be expected as one passes?

*** Do not confuse shelf clouds with wall clouds, shelf clouds do not rotate -Shelf cloud: large, low hanging, typically non-precipitating -sign strong storm is approaching Review answers: - Shelf cloud is associated with a MCS - it is before the convective region - its forming becasue we have warm moist air rising over the gust front - Shelf cloud does not rotate - it does not do anything it is a warning cloud

How does the temperature of air change as it rises and sinks? Why?

- As air rises it expands and cools - as air sinks it warms and contracts

MCS Radar

- Know where heavy precip - know low precip (in back) - Know that in. front is the shelf cloud - most heavy precip is in the bow echo (convective zone) - Stringer part can be called a squal line - area of lighter rain is the training stritiform region

Know basic lightning safety.

- Safest place is your car and house - stay away from corded electronics and water - Unsafe places are golf course, under a tree, any place you are the tallest object - dont lie on the ground - crouch down on the balls of your feet - minimize your contact with the ground

How are lightning and thunder related? How is thunder created?

- The lighting heats the air around the bolt to 30,000c - The air rapidly expands creating a huge pressure range - A flash of lighting is seen but not heard - Inversions conduct sounds waves resulting in louder thunder

Why is moisture important to thunderstorm formation?

- fuel for the storm is warm moist air - Td at least 60F - energy source = the production of cloud (condensation), releases latent heat - cant have instability without moisture, moisture supply: - primary is the gulf of Mexico - secondary is evaporation from the soil and evapotranspiration from vegetation (corn sweat)

When and where are thunderstorms most common in the United States? Why?

- most common march - September but can happen any time of year - most common in southeast US

Why do supercells typically persist for much longer than ordinary thunderstorms?

-A separate updraft and downdraft allows the supercell to be long-lived because it reduces the likelihood that too much rain-cooled, stable air from the downdraft region will be ingested into the updraft, causing the storm to weaken *correct me if wrong, i looked it up

What are typical lifting mechanisms that can trigger thunderstorms?

-Fronts -orographic lift: atmosphere heats from the ground up, air over mountain warmer than air around it rises -Seabreeze -rising thermals of air: the surface air just gets hot enough in some locations to start to rise like a bubble, these are ordinary thunderstorms not going to be severe

Know tornado safety.

-Get to the lowest floor of a substantial structure, basements preferred -Don't waste time opening or closing windows!! The tornado will do this for you! -Get to an interior room on the lowest floor of a sturdy structure Put as many walls between you and the tornado as possible -Stay away from windows -Protect yourself from flying debris: • Mattress• Bike helmet• Wear shoes -If you have no basement, interior bathrooms or closets are best -Don't wait for sirens to sound (only meant to be heard outdoors) or to see the tornado -Take shelter when you hear the warning -Avoid large rooms, including auditoriums, gymnasiums, and big box stores

Know hail safety.

-If outdoors, get inside -If in a car, pull over to a safe place and cover your eyes/face if glass is breaking -Do NOT block roadways/hide under overpasses to seek shelter from hail -Indoors, stay away from windows

What is a multiple vortex tornado? How are they different than regular tornadoes?

-Initially, a tornado is composed of a single, rotating column with ascending air in the center -Extremely low pressure in the center near the surface leads to the formation of a downdraft in the center of strong tornadoes -Tornado widens as downdraft hits the ground -The rotation associated with the tornado breaks into the suction vortices

What is an inversion and how does it relate to stability?

-Inversions promote stability within the vertical layer of the troposphere they exist. - The inversion created from a cold front is especially evident when a shallow layer of polar air moves into lower latitudes. The air associated with the shallow air mass is colder than the air aloft, thus creating an inversion. - Inversion is where the air gets hotter as you go up in the atmosphere - Warm air tends to rise - warm air on top of cold air is comftorable and it is stable - warm air below cold air is not stable - inversions = stability - The stratosphere is very stable

Know what the different parts of a supercell looks like on a radar.

-Know hook echo - rear flank downdraft - forward flank downdraft - and where the hail core is

What is the life cycle of a tornado? Why do they dissipate?

-Lifetime ranges from seconds to an hour -Not completely sure why some tornadoes last for a long time whie other do not -Funnel becomes deformed -Winds inside of storm blow in different directions aloft and near ground -Circulation forms an elongated rope shape ("roping out") -Cold outflow air wraps around tornado -Cold air not buoyant, does not rise

What are mammatus clouds? Are they dangerous?

-Mammatus clouds are sometimes seen underneath the anvils of thunderstorms -They can be beautiful but are not threatening

What is a mesocyclone? How does it form?

-Rotating updraft of the super cell -The wind shear in the lowest 1.5km of the atmosphere creates horizontally rotating tubes of spinning air -The updraft of a developing thunderstorm tilts this horizontally rotating tube upward ... the updraft begins to rotate about a vertical axis -Mesocyclones are often visually manifested by stunning structure, including cloud striations - sucks up the rotation from sheer - have to have sheer - mesoscyclone is a rotating updraft and its caused by sheer.

What is a wall cloud? How does it form?

-Sometimes rotate -Defined as a lowered cloud base beneath the updraft -Tornadoes can develop from rotating wall clouds -Inflow of warm moist air -Wall clouds form as a storm ingests humid, rotating air from forward-flank downdraft -A wall cloud is a lowered cloud beneath the updraft base

What is a gust front or outflow boundary?

-The boundary between cold outflow and warm inflow is called gust front or outflow boundary -Therefore, the temperature drops, and winds increase just before a thunderstorm begins -Also, why it is cooler just after a thunderstorm -Convergence at outflow boundary may trigger new storms -Gust front: cool blast of air that formed in the downdraft of the thunderstorm Review answeres: -Cool air pushing outward is gus front forms downdraft from precipitation

Are cars safe from lightning? What about airplanes?

-The safest place in a lighting storm is a car - Depends on the strength of the lighting, lighting could destroy power in a plane

Do mountains, cities, lakes, or bodies of water prevent tornadoes?

-Tornadoes that form on land can cross bodies of water, including rivers and lakes -Tornadoes can also form on water. These tornadoes are called "waterspouts" -Never think that a body of water will protect you from a tornado

What does a supercell updraft look like? The FFD? The RFD?

-Updraft visually manifested by cumuliform cloud -When storms rain into their updrafts, they quickly dissipate, strong winds aloft in supercell environments blow precipitation out of the updrafts, allowing supercells to persist much longer than ordinary thunderstorms *Updraft base is rain free Review Answers: - updraft base is rain free - and we may see some rotation

What is outflow? How does it form?

-When the cold downdraft reaches ground, it spreads outward -Forms pool of cold air at surface beneath storm -Known as cold pool or outflow

What are the criteria used by the National Weather Service to determine if a storm is severe?

-Winds: greater 50 kts (58mph) -Hail: 1" + in diameter - if there is a tornado the storm is considered severe *have one of the three

What is heat lightning? Is it real?

-a storm that is so far away that you can only see the lightning but not hear the thunder; - not real-it is actually "sheet lightning"

What is the typical life cycle of an ordinary thunderstorm?

-usually lasts less than an hour Stages: -cumulus stage -mature stage *precipitation is required to form a downdraft -dissipation stage stages of development: 1) mesocyclone first 2)development of wall cloud 3) and then tornado once formed: 1) Single vortex (small) 2) multi vortex (largest) 3)rope stage (dying tornado)

What is a bow echo and what is the main weather hazard associated with them?

1) Bow echo = section of high radar reflectivity (intense storms) that "bow" outward 2) When meteorologists see a bow echo, it will usually result in a severe thunderstormwarning being issued -these types of storms are notorious for producing damaging, straight-line winds

What is the supercell spectrum?

1) Classic Supercells Spectrum -Little rain near updraft, significant precipitation within forward flank -Stunning storm structure often visible from south -Most prolific tornado producers 2) Heavy-percipitation (HP) Supercells Specturm -Significant precipitation near updraft often obscures storm structure and/or tornadoes -Prolific hail-wind producers 3) LP - low percipitation

How does hail form? What type of thunderstorm produces the largest hail? Where do you find the most hail in that type of thunderstorm?

1) Hail formation -Hail embryo is small ice particle suspended in updraft -Supercooled water within updraft freezes to hail embryo and partile grows -A stronger updraft can suspend a heavier and thus larger hailstone -Hailstone falls back to earth when it is ejected from the updraft 2) How to get big hail? -Large instability (strong updrafts) -Strong wind shear, enabling supercell formation (stronger updrafts) -Cooler temperatures/drier air (less melting on the way down) **Largest hail falls fastest and thus closest to updraft 3) updraft??? Review answers: - Largest hail comes from supercells - going to be closest to the updraft -

What are the three thunderstorm types?

1) Ordinary (single cell) thunderstorms -Usually not severe -Form in environments with weak vertical wind shear -Most common -Can last about an hour to when they're formed to when they dissipate -Generally, develop in regimes of weak vertical wind shear 2) Mesoscale Convective Systems (MCS) -An MCS is a large complex of thunderstorms -Can cover an entire state -Often produce significant rainfall -Important for agriculture -Hazards include flooding, straight-line winds, and the occasional tornado 3) Supercell Thunderstorms -Supercell thunderstorms are long-lived rotating thunderstorms -Can last for hours -Often isolated -Most intense thunderstorms on the planet -Most rare type of thunderstorm -*Always rotate* -Typically, single celled and small (county or smaller) -Produce majority of tornadoes -All EF-2+ tornadoes -Produce nearly all hail, golf ball-sized or larger -Severe aspects: tornadoes, hail, straight-line winds -Typically smaller than a county

What is the difference between a watch and warning?

1) Watches = Conditions are Favorable for Severe Weather -When a severe thunderstorm or tornado watch is issued, it means conditions are favorable for severe thunderstorms or tornadoes Conditions: -Surface moisture (look at sfc. Td map) -Lifting mechanism (look at weather maps for fronts) -Unstable atmos. (look on sounding for CAPE and negative lifted index) -Wind shear (look at sounding - change in speed and/or direction) 2) Warnings = Severe Weather is Happening Now! Tornado warnings -A warning has been sighted -By an official (ex. Police officer) -By a trained storm spotter) -Doppler radar has detected rotation within a storm or tornado debris Severe Thunderstorms Warning -Hail 1 inch or greater -Doppler radar detects winds > 50 kts -Weather station observers' winds > 50 kts -Storm spotter or official reports hail > 1 inch or wind damage

What are downbursts and microbursts? How do they form?

1) What is a downburst? -Strong downdraft that comes in contact with the ground -Microbursts are smaller (and often more intense) downburst 2) How do downbursts form? -Sinking air is colder than the air around it -Rain falls into unsaturated air and evaporates -Cooling the air -Cold air sinks -Rain drags air downward with it -Downbursts can sink as fast as 40-50 mph -Aviation hazard **Microburst = smaller and more intense downburst Review Answers - Downburst and micro burst are very fast intense moving downdrafts

What are the three ingredients for thunderstorm formation? What additional ingredient is needed for severe thunderstorm formation?

1) an unstable atmosphere 2) lifting mechanism -Trigger mechanism: Anything that can cause the air to rise 3) surface moisture Severe thunderstorm: 4) vertical wind shear -Decides if storm is severe or not, helps storm organize and rotate -Role of wind shear: to separate the updraft from the downdraft and allow the storm to rotate -Where to find wind shear: winds do not increase or change direction with height (no shear), Winds increase and/or change direction with height (lots of shear) Review answers: 1) thunderstorms need instability 2) negative lifted index means that the parcel line is warmer than the environment 3) to find if the lifted index is negative go to 500 mb and subtract the parcel temp from the environment temp

Review the main components of a squall line - Gust front and shelf cloud, convective zone, and trailing stratiform region. What are the characteristics of each?

1) gust front -The gust front forms a line, Linear lifting along the gust front results in a line of thunderstorms -Gust front outruns thunderstorms (no lift; storms become surrounded by cold air) -Gust front: cool blast of air that formed in the downdraft of the thunderstorm 2) shelf cloud -Shelf cloud: large, low hanging, typically non-precipitating -*** Do not confuse shelf clouds with wall clouds, shelf clouds do not rotate 3) convective zone -Line of thunderstorms just behind gust front -Heavy rain, strong gusty winds -Line of high reflectivity (yellow/reds) on image 4) stratiform region -Stratiform precipitation develops behind the line of thunderstorms -Large area of light to moderate rain behind convective zone -Trailing stratiform region = light to moderate rain that follows the intense leading thunderstorms, can contain lightning

Review the sequence of events of a lightning strike

1) stepped leader 2) return stroke -When they meet -Electrons from cloud base suddenly rush down the open path -Current travels back up producing the bright flash -Travels at 10,000,000+ mph -Heats air to 30,000 C 3) return stroke opens an ionized path -Any remaining electrons from cloud base can then rush back down the same path -Called the dart leader 4) second return stroke -When it meets the positive charge -Second bright flash -Can occur multiple times Ryan (review answers) - focus on negative polarity: - Distribution of charges - positive on top negative on bottom in cloud - positive on surface so it looks for the path of least resistance - streamers come down and try to find the path of least risistance and then come back up - KNOW: Strike we see is called the return stroke. - KNOW: after return stroke you can have more than one stroke -Understand: cant perdict exactly where lightning is going to strike - lighting does strike the same place more than one -Step leader: the electrons that are searching for the path of least resistance (Cant see ) - Streamers = step leaders -positive polarity: - stronger

What is the updraft? Downdraft? Overshooting top? Anvil? How do they form?

1) updraft -warm moist air that rises --> cools --> condensation = clouds -Updraft visually manifested by cumuliform cloud -When storms rain into their updrafts, they quickly dissipate, strong winds aloft in supercell environments blow precipitation out of the updrafts, allowing supercells to persist much longer than ordinary thunderstorms *Updraft base is rain free 2) downdraft -Some rain evaporated as it fell = cooling -Precipitation falls and drags the air downward -Result: cold dense pocket of rapidly descending air loaded with precipitation 3) overshooting top -An overshooting top is a dome-like protrusion shooting out of the top of the anvil of a thunderstorm and into the lower stratosphere -When an overshooting top is present for 10 minutes or longer, it is a strong indication that the storm is severe. 4) anvil Air diverges outward when it reaches tropopause, forming an anvil cloud at top of storm -formed at equilibrium level -Strong shear (strong winds aloft) in supercell environments often yields long, asymmetric anvils Review answer for anvil - anvil is the cloud top that is pushing to the side - overshooting top is the part that pushes through the anvil every once in a while

super cell tornados

1) wall cloud rotations comes from the forward flank downdraft 2)tornado rotation comes from the rear flank downdraft

How are tornadoes rated? On what basis?

Basis: Damage. Tornado winds usually not measured directly Assigning value: F0 - F5 (EF0 - EF5) Problems: 1) Subjective Assessment (experience of the surveyor) 2) Non-uniform construction standards 3) Only know the strength after a damage survey 4) If the tornado hits nothing, it can be rated lower than maximum intensity Review Answers - EF scale - based on debris - bassicly based on the damage caused - Cant tell the strength of the storm until afterwords - goes 0 - 5 five is the strongest - the strength of the tornado runs into issues because building are built differently based on location in country and can only tell strength after the tornado has done the damage and different scientists have different opinion/scales

What is the LCL? LFC? EL? LI? CAPE? Know how to find each on a sounding and how they relate to cloud structure

LCL: lifting condensation level, (Kink in the parcel line where a cloud is forming, can be seen or noticed by a sharp change in direction of the temperature line) - cloud base - the altitude to which the air must be lifted for condensation to begin - as air rises it cools cooling the air, increases RH - at the LCL the T= Td - the rh = 100% and a cloud forms LFC: level of free convection (the first time the parcel line crosses the temperature line on a sounding chart, after this it becomes boyant) - the point above the ground that the parcel first becomes warmer than its environment - the parcel can rise on its own because it is boyant, - this is where the unstable part of the storm forms - cloud begins to bubble EL: equilibrium level (second time that the parcel line crosses the temperature line on a sounding chart, this is the cloud top) - the point where the anvil forms - Air hits the stable warm air in the stratosphere and spreads out horizontally - marks the top of the storm LI: lifted index -the difference between the environment and parcel @500 mb CAPE: all the palces that the parcel is warmer than the environment would be a cape

How do non-supercell tornadoes form? What are they called?

Landspouts and waterspouts: - Preexisting circulation at surface along wind shift stretched by updraft - No downdraft or supercell required - Can occur with supercells, ordinary thunderstorms, or MCSs - Usually less intense than supercell tornadoes, but still dangerous REview answer - Yes they are possible and we can have them in squal lines - can have water spouts and land spouts - they are going to be wekaer than supercell tornados

What is atmospheric instability? How does it relate to an air parcel?

Parcel: blob of air Environment: the air outside of the parcel Adiabatic process: no heating or mixing of the air in the environment with the air in the parcel KEY IDEA: - compare the temp of the parcel to the temperature of the environment - if the temp of the parcel is warmer than the temp of the environment it can rise (warm air is less dense) Review answers: - Temerature - parcel that is warmer than the environment it is going to create instability - rising air creates clouds, clouds make thunderstorm, etc - for severe weather you want a negative lifted index

What is a derecho?

Review answers: - a very long lasting wind event - very long MCS event

What is the typical electric change separation inside of and near a thunderstorm? What causes this charge separation?

Review answers: lighting- base of cloud is going to be negative positive is going to be at the top, the negative charges in the base of the cloud are going to pull up some of the positive charges on the ground

What is a supercell? A hook echo?

Supercell: -When storms rain into their updrafts, they quickly dissipate, strong winds aloft in supercell environments blow precipitation out of the updrafts, allowing supercells to persist much longer than ordinary thunderstorms 1) Supercell Structure -Forward-flank downdraft (most of the rain falls here) -Rear-flank downdraft (co-located with the hook echo) -Hail core -Strong winds aloft blow precipitation away from the updraft -Precipitation falls downwind of updraft, forms forward-flank downdraft -Heaviest precipitation falls adjacent to updraft Hook Echo: -Hook echo originates from precipitation particles rotating around the updraft -First hook echo ever seen in Urbana, IL in April 9, 1953

Where in the United States are tornadoes most likely?

Tornado Alley and Dixie Alley: MOst likely: - peak in may/june most common in the late afternoon/ evening (4:00-6:00 PM) needs 4 ingrediants: 1)moisture 2)instability 3) trigger mechanism 4) sheer

Tornado Genesis

Wall cloud -> forward flank downdraft Tornado -> rear flank downdraft mesocyclone-> environmental sheer

What is the definition of a tornado?

a mobile, destructive vortex of violently rotating winds having the appearance of a funnel-shaped cloud and advancing beneath a large storm system *i looked it up, could be wrong

Which type of supercell is the most prolific tornado producer?

classic supercells

Review the lightning myth or fact exercise

refer to slides

Why do ordinary thunderstorms typically only last for about an hour?

the downdrafts begin to cut off the updrafts *correct me if im wrong, i just looked it up

How often does each type of severe weather occur in the US each year?

thunderstorm season: march-sept, but can happen any time of year Tornado: 1400 Hail: 3 to 5 thousand Wind: 12 to 14 thousand

When (during a year and during a day) are tornadoes most likely? Why?

year: april-july day: hour 14-hour 20 why: ???