Weather Test #3
Explain the difference between positive and negative polarity lightning and know how to draw both on a cloud. Label the charges on the cloud and ground.
Positive charge accumulates toward the top of the cloud Negative charge accumulates toward the bottom of the cloud The negative cloud bottom induces a positive charge on the ground o Electrons on the ground are repelled away by the negative (same) charge
What is a bow echo? What type of thunderstorm is it associated with? What type of severe weather does it signify? How does it differ from a hook echo?
1. Line of thunderstorms having an arc or bow shape 2. Associated with strong straight-line winds
Calculate the probability of a flood based on its occurrence interval (10yr, 20yr, 100yr, etc)
100 divided by x 10yr - 10% 20yr - 5% 100yr - 1%
*What are the three ingredients needed to form a thunderstorm?
A lifting mechanism, unstable atmosphere, enough moisture
What is the mesocyclone, where in a cloud can it be found and how does it relate to the formation of a tornado?
A mesocyclone is a vertical column of cyclonically rotating air within a thunderstorm (much larger than a tornado). Tornadoes develop out of the wall cloud of a supercell and the wall cloud develops out of the mesocyclone.
*What is the difference between a tornado and a funnel cloud?
A tornado is a column of air that rotates violently around a small area of intense low pressure. -Rotation reaches all the way from cloud to ground A funnel cloud is when the tornadic circulation does not reach the ground.
What is the difference between a wet and dry downburst?
A wet downburst is accompanied by measurable precipitation meanwhile dry downbursts have no measurable precipitation because rain evaporates
Explain why wind shear allows the formation of a severe thunderstorm
As it keeps the updraft and downdraft separate, this allows for the thunderstorm to grow larger and last longer
*If you looked at an image of the damage due to a tornado, how would you know it is an EF5?
Because of the structural damage, only a foundation would remain
Describe a few different ways in which the air is forced to rise (in order to form a cloud and a thunderstorm)
Convection - warm air near the earth's surface rises Convergence - air rises when piled up at the surface Topography - air can't go through mountains, goes up the mountain Fronts - warm air mass rises above the cold air mass
What is a derecho? How does it differ from a tornado?
Derecho - Strong, long-lived, non-rotating wind event Can be observed with squall lines or MCCs Not as common as tornadoes Normally larger scale than tornadoes Radar signature is a bow echo Can last several hours to a day Usually a straight line wind event causing a long path of wind damage, which is not associated with a tornado
*What is the name of the scale used to classify tornadoes? What was the original scale? What is the currently used updated scale?
Enhanced Fujita Scale (originally was the classic Fujita scale) ranges from EF0-EF5
What are the two mechanisms at work in a downburst?
Evaporation of falling drops -Droplets take energy from the environment to evaporate -Environment cools in response -Cooler air, denser, sinks Drag due to precipitation -Falling precipitation pushes air downward and weighs air mass down towards the earth's surface
Describe safety precautions that should and should not be taken during a tornado.
Go to a basement -If no basement, go to an interior room in lowest level --Away from windows --Bathroom, closet, etc. Do not waste time trying to open windows -If outside, try to get inside --If not, go to ditch --Not inside a car Protect neck and head
*What are the three specific criteria used to officially classify a thunderstorm as severe? Do they all have to occur or is one of them enough?
Hail 1-inch or larger, a tornado, and high winds of at least 50 knots *You only need 1 of the 3 for the thunderstorm to be considered severe
*Draw a hook echo and mark the spot where a tornado could form.
Hook echo - -Radar signature of a supercell with very strong rotation -Tornado can be produced near the center of the hook
What is a thunderstorm? What type of cloud is involved in its occurrence?
It is a cloud/storm that produces thunder and lightning. A cumulonimbus (Cb) cloud is needed.
*Use a sounding chart to determine the Lifted Index and use the Lifted Index to determine if the atmosphere is stable or unstable.
LI = T(environment @ 500 hPa) - T(parcel lifted to 500 Negative LI - unstable conditions at 500 hPa (since parcel warmer than environment) Positive LI - stable conditions at 500 hPa (since parcel colder than environment) Possible weather: LI > 2 - No significant activity 0 < LI < 2 - Showers or thunderstorms possible with other source of lift -2 < LI < 0 - Thunderstorms possible -4 < LI < -2 - Thunderstorms more probable, but few, if any severe LI < -4 - Severe thunderstorms possible *Large negative number - severe weather *Large positive number - very nice weather
What are the two subtypes of downbursts?
Macroburst -A downburst with winds extending for more than 4 km, with peak winds lasting 5 - 20 minutes (term not used too often) Microburst -A downburst with winds extending for less than 4 km, with peak winds lasting 2 - 5 minutes
Explain the two ways in which radar can be used to determine the possibility of a tornado. Name and explain them.
Modern Doppler radars can measure not only reflectivity (radiation reflected back to the instrument), but also wind speed away or toward the radar Consecutive pixels with opposite wind direction (velocity couplet) indicate rotation This is the mesocyclone The actual tornado cannot be seen with regular equipment
*What is a tornado family?
One storm that produces several tornadoes
What is hail, and how does it form?
Pellets of frozen rain that fall in showers from cumulonimbus clouds. They form when rain droplets get pushed high into the atmosphere by updrafts, freeze and then fall. They can get larger if they keep getting pushed up into the atmosphere.
*If you were given a sounding, tell me what the 3 following lines mean?
Red line - T environment Yellow line - T parcel Black dotted line - Dew point *Which 2 are used to determine stability? The red and yellow line
List the four types of thunderstorms
Single Cell Thunderstorms -Air mass thunderstorms -Supercells Multi-cell Thunderstorms -Squall lines -Mesoscale Convective Complexes (MCCs)
How do tornadoes and hurricanes compare to each other in size, duration, and windspeed?
Size - tornadoes are 10s of feet to a couple miles wide while hurricanes are 500-1,000 miles wide Duration - tornadoes last mins to hours while hurricanes last days to weeks Windspeed - tornadoes are classified from Ef0-EF5 and range in windspeed from 65mph to over 200mph while hurricanes are classified using the Saffir Simpson Scale from category 1 through 5 ranging from 74 mph to over 155mph
How many seconds does it take between a flash of lightning and the sound of thunder to reach our ears (hint, this is the trick for determining how far away lightning is)
Sound takes longer to reach our ears o 5 seconds per mile (or 3 secs. per km) Example: o If ten seconds pass between the flash and the thunder, it happened 2 miles away
*Explain the 4 steps of a lightning strike
Stepped leader - Initial flow of electrons toward the earth Return stroke - When the electrons meet a positive feeler Dart leaders - not all charge is used up by initial discharge Subsequent return stroke - Several occur until out of negative charge in the cloud is "emptied" - (this is why lightning appears to flicker) Exercise 3.8
Where is tornado alley? Name states in the heart of tornado alley.
Texas, Nebraska, and Oklahoma
*What happens to Air parcel for unstable atmosphere?
The air parcel rises
Describe what the air does when the atmosphere is stable and when it is unstable.
The atmosphere is unstable if rising air is warmer than its surroundings T parcel > T environment AKA: The air parcel is warmer than the environment around it
How do the old scale and the new scale compare? How are they different and what is the same?
The two scales are equivalent in the sense that an F4 and an EF4 would produce the same kind of damage. The difference is in the winds that are estimated to have caused that damage EF scale based on exhaustive engineering studies of how wind affects structures -Wind speeds considered more accurate
*What is the difference between a tornado watch and a tornado warning?
Tornado Watch - Conditions are favorable for the development of storms with the potential to form tornadoes Tornado Warning - A tornado has been spotted or radar has indicated a storm with strong rotation and capable of producing a tornado at any time
Explain some basic causes of flooding
Tropical cyclones Stationary front overrunning Frequent storms over the same area Mountain topography
Explain how the strength of a tornado is determined
Weak (mph) (damage) -EF0 65 - 85 light (branches) -EF1 86 - 110 moderate (windows, roofs) Strong -EF2 111 - 135 considerable (trees, trailers) -EF3 136 - 165 severe (cars, walls) Violent -EF4 166 - 200 devastating (houses) -EF5 over 200 incredible (everything)
*What is a tornado outbreak?
When a large number of tornadoes form over a particular region
*What is the additional ingredient needed to make the thunderstorm severe?
Wind Shear
What is a downburst?
a strong downdraft that comes in contact with the ground and winds can exceed 100mph