Storms & Tornadoes

what is a front?

* boundary between two air masses w/ contrasting temperatures

what is a cold front?

* cold air mass advances under a warm air mass
* warm air mass rises
* heavy precipitation (e.g., thunderstorms) result along a narrow band

→ tend to get storms

what is a water front?

* advancing warm air rises slowly over the adjacent cooler air mass
* associated w/ widespread clouds w/ moderate steady precipitation

→ gradual rise → less intense precipitation

what is an occluded front?

* when advancing cold front overtakes a warm front
* warm air no longer intersect the ground surface

→ warm air not interacting w/ surface

note: cold air travels faster

what is a stationary front?

* occurs when cold air flows nearly parrallel to the front, while warm air rises over the front
* position does not move; can lead to floods, ice storms and heavy snowfall
* warm air cant push cold air → get precipitation to same location for long period of time

is jet stream air flow even or uneven?

* uneven
* more air flow out of a region than into it → leads to deficit in jet stream which results in low p

what is divergence in jet stream?

* an air deficit at the tropopause
* creates low p center
* surface air rises into low-p
* mid-latitude cyclones evolve → is created
* \

mid-latitude cyclone evolution 1

* warm air flows up and over the fronts
* widespread area of clouds and rain along te warm front; showers and thunderstorms along the cold front

mid-latitude cyclone evolution 2

* cold front moves faster than warm front
* as air spirals counterclockwise, the cold front begins the catch up to the warm front
* warm front migrates NW

mid latitude cyclone evolution 3

* cold front catches up and overtakes the warm front; an occluded front devs
* mid-latitude cyclone has a “comma” shape
* once occluded, the sys will lose energy and dissipate ending the mid-latitude cyclone event

what is the head of the comma?

* in winter, home to blizzards and ice storms

what is the tail of the comma?

* thunderstorms, tornadoes, windstorms blizzard

what is a thunderstorm?

* towering cloud that produces lightning and thunder
* usually have strong winds, heavy rains, and sometimes hair

what are the conditions required to dev a thunderstorm?

1. moist air (mostly from oceans, lakes, and wetlands)
2. a lifting mecha
3. atmospheric instability

lifting mechanism

* movement along a front
* high relief fording air upwards
* e.g., mountains
* localized heating of the ground surface

what is a gust front?

* thunderstorms create cold downdrafts
* downdrafts act like small cold fronts

what is unstable air?

* when air parcel is less dense than its enviro

what is adiabatic expansion?

* air parcel expands and cools as it rises
* dry adiabatic lapse rate (\~10ºC/km)
* Saturated (moist) Adiabatic Lapse \n Rate (\~6ºC/km)

what is environmental lapse rate?

* rate temperature drops with increasing altitude in the atmosphere.

atmos instability

* if air parcel rise if warmer than enviro (atmos) → it keeps going up and creates thunderstorm
* if remains colder than atmos, stop rising, go back donw

ordinary cell

* cumulus: warm humid air rises (updraft) and condenses to form a cloud
* mature: precipitation fall; downfall devs
* dissipating: rain cools the air and ground, downdraft suppresses updraft

squall line thunderstorm

* acts like a giant cold front
* lifting is focused along strong, advancing cold fronts

what are frontal squall lines?

* thunderstorms occurring in a vv long line
* often seen along the “tail” of a mid-latitude cyclone
* associated w/ heavy rain, lightning, and straight-line winds; can damage buildings and trees

what is a radar?

* well-defined line of thunderstorms is visible
* the well-defined line lies along advancing cold front

what is a derecho?

* spanish for “direct” or “straight”
* severed straight-line winds over a large geographic region
* may dev along squall-line thunderstorms

derecho, Ontario May 2022

* winds up to 190km/h
* impacted 15.6 million people
* power outages impacted 1.1 million people, some for over a week
* some homes were comp destroyed
* 11 people died; most from falling trees

what is a supercell thunderstorms?

* differ from ordinary cell due to rotational motion of the upward-moving air
* they dev when wind directions near the surface are diff from conditions higher in the troposphere

supercell thunderstorms?

* strong winds in upper atmos cause the storm tilt, so updraft isn’t vertical
* there are 2 downdrafts
* downdraft cant cut off updraft cuz lower so last longer

supercell thunderstorms

* forward flank: NE side of NE-moving supercell
* strong wind at forward flank downdraft (FFD)
* rear flank: SW side of NE-moving supercell
* rear flank downdraft (RFD)
* can produce tornadoes

what is lightning?

* an electrostatic discharge in the atmos that occurs when negatively and positively charged particles become separated

when can charge separation occur in lightening?

* as particles collide in a cloud during a thunderstorm

hazards of lightning?

* damage to trees and homes
* start forest fires
* power outages
* can injure or kill humans that are struck; can cause burns, paralysis, organ damage
* kills approx 7 canadians each each (global \~2,000

\- 6,000)

what is thunder?

* the sound generated by lightning

what can lightning temp reach?

30,000ºC

how is thunder generated?

* lightning stroke instantly heats the air around it, \n causing it to expand explosively.
* When the lightning stroke ends, air contracts violently.
* contracts = collapse
* The sudden expansion and contraction of air generates thunder.

what are downbursts?

* formed by a rapidly descending mass of cold air from a thunderstorm

what is hail?

* associated w/ intense thunderstorm activity
* dev of large hailstones (golf ball-size) requires strong updrafts so snow can’t fall
* longer it stays in atmos → bigger it grows

what is a tornado?

* a violently rotating column of air extending downward from the base of a severe thunderstorm to the groud

→ leaves scars → tornado track

what is a tornado track?

* the path a tornado takes across the ground

what is a tornado outbreak?

* when multiple tornadoes are produced from storms

supercell tornado formation

* is most devastating
* there is a rear-flank downdraft
* forward-flank downdraft
* and updraft

when are tornado watches issues?

* when thunderstorms are capable of producing tornadoes

when are tornado warmings issues?

* if a tornado is spotted or Doppler radar show signs of rotation

multiple-vortex tornadoes

* top right → blue shows that air sucks down in middle
* bottom left → downwards air helps widen it and can split tornado

non-supercell tornadoes

* dev along squall lines and in hurricanes
* sig horizontal wind shear is needed for vortices to dev
* updrafts may lift and stretch vortices into tornadoes
* hurricane rain band shear may also cause tornadoes
* generally weaker than supercell tornadoes
* this is vertical air movement

what is the enhanced Fujita Scale?

* is used to classify the intensity of a tornado
* based on wind speed thresholds and linked to their associated damage
* a tornado is classified on the Enhanced Fujita Scale based on the max damage it causes along its path, they evolve over time
* they first grow in strength, then dies
* can be one rating at some point, or another

Jopling, Missouri tornado

* 158 deaths
* $3 billion of damage
* homes wiped off foundation
* medical center sustained so much damage it had to be demolished

Canada tornado geography

Barrie, Ontario tornado

* cluster of 2 EF2 tornadoes
* $75 million in damage
* 110 homes damaged

how to survive a tornado?

* move to a tornado shelter, basement or interior room
* protect your head using a helmet is available
* highway overpasses are not safe locations. wind speeds can be amplified
* cars provide only modest protection

what can mid-latitude cyclones cause?

* blizzards, thunderstorms, nor’easters (storms called in Atlantic Canada)