Unit 12

a thunderstorm cloud is a _____ cluod.

cumulonimbus

a severe thunderstorm cell may be accompanied by....

damaging surface winds, hail, heavy rainfall, frequent lightning

Modern weather radar can operate in either the reflectivity of Doppler mode. The principal advantage of the Doppler over the reflectivity mode is Doppler's ability to

determine the detailed circulation of air within a thunderstorm cell.

the dissipating stage of the life cyclone of a thunderstorm cell is characterized by

downdrafts only

in the southern great plans, tornadoes are most likely to develop when

dry pacific air overlies a layer of maritime tropical air

roll cloud

elongated cylindrical dark cloud that appears to rotate slowly about its horizontal axis - occurs behind the gust front and beneath, but detached from, a cumulonimbus cloud; roll clouds are seldom accompanied by severe weather

Doppler radar can detect

falling rain, a mesocyclone, gust front, wind shear

which type of lightning is most common in the US?

intracloud

a dry line

is a likely site for development of a sever thunderstorm cell, separates hot, dry air from warm, humid air, often occurs over Texas and Oklahoma

hail

is produced in cumulonimbus clouds

Tornadoes are most likely to develop

over flat, moist terrain

Why do capping (subsidence) inversions favor the development of severe thunderstorms?

If you have a cap inversion - a stable layer above the surface - you have a pressure cooker and it keeps building until the stable layer pops

over the course of a year which one of the following states likely will experience the most tornadoes? Oregon, ND, Kansas, MA, Arizona

Kansas

hail

precipitation in the form of balls or lumps of ice

condition(s) needed for the development of a tornadic circulation within a thunderstorm is (are)...

strong updraft, strong vertical shear in horizontal wind, development of a mesocyclone

Hail is most likely to be produced by thunderstorm cells that are characterized by...

strong updrafts, great vertical development, an abundant supply of supercooled water droplets

The cumulus stage of the life cycle of a thunderstorm cell is characterized by

updrafts only

what are the three conditions required for thunderstorm formation?

1) humid air in the low-to mid-troposphere 2) instability 3) source of uplift

height of tornado

1-3km

lateral diameter of tornado

100-300 meters

how far away is a lightning stroke, if you hear the thunder 10 seconds after you see the flash?

2 miles

lateral speed of tornado

25-40 mph

the typical life expectancy of a thunderstorm cell is

30 min

life time of tornado

30-40min

path length of tornado

40 mi

in the US, the months of peak tornado activity are

April, May, and June

a weak tornado has a life expectancy of

1 to 3 minutes

thunder is the consequence of

a rapidly expanding hot air channel

flash flood

a sudden overflow of a river channel or other drainage way, often caused by torrential rains associated with thunderstorm activity

a feature sometimes present in thunderstorms that may prolong the mature stage is...

a tilted updraft

tornado

a whirling column of air in contact with the ground that is almost always produced by a thudnerstorm

most thunderstorms do not extend very far upward into the stratosphere primarily because the air in the stratosphere is....

absolutely stable

severe thunderstorms

accompanied by locally damaging winds, frequent lightning, or large hail - as general rule: the greater the altitude of the top of a thunderstorm, the more likely it is that the system will produce severe weather

downburst

an exceptionally strong downdraft that, upon striking the earth's surface, diverges horizontally as a surge of potentially destructive winds - occur with or without rain

stretching of a vertical column of air in the mesocyclone will cause

an increase in the spin rate of the air about a smaller radius

weather radar

an indispensable tool for detecting and tracking severe weather systems and providing the public with advance warning of the approach of hazardous weather

cumulus congestus

an upward-building convective cloud with vertical development between a cumulus cloud and a cumulonimbus cloud

Weather Warning

applies when hazardous weather is taking place somewhere in the region or is imminent. people are advised to take all necessary safety precautions.Â

thunderstorm cells occur...

as components of a squall line, in the ITCZ, in a mesoscale convective complex, along a gust front

F-Scale

based on rotational wind speeds estimated from property damage and categorizes tornadoes as <i>weak</i> (F0, F1) <i>strong </i>(F2, F3) or <i>violent</i> (207 and higher wind speed)(F4, F5)

thunderstorm development is favoredÂ

by conditionally unstable maritime tropical air

in the US, thunderstorms are most frequent in

central flordia

what areas of the US experience the most thunderstorms annually?

central florida

the anvil top of a thunderstorm cloud is likely to be a ______ cloud composed of ______

cirrus...ice crystals

multicell line

commonly called a squall line, this type represents a long line of organized line of thunderstorm cells with a continuous gust front as a leading edge associated with strong vertical motions. a squall line may develop ahead of an advancing cold front and offer a moderate threat of severe thunderstorms

a mesoscale convective complex (MCC)

consists of numerous interacting thunderstorms

convective condensation level

continuous stream of bubbles or warm, unsaturated air cool at the dry adiabatic lapse rate until they reach this where water vapor condenses and cumulus clouds start forming - the more humid the air is to begin with, the less expansional cooling that is needed for the bubbles to achieve saturation and the lower is the base of cumulus clouds

forced convection

convective currents are strengthened by frontal or orographic lifting or convergence of surface winds, most thunderstorms are products of forced convection

Virga is sometimes mistaken for a tornado because of itsÂ

cylindrical or funnel shape

can you determine how far a lighting strike will be by estimating the time lag for the thunder to reach you?

distance in miles= elapsed time in secs       5

thunderstorm development is trigged by

forced convection, uplift along a well-defined cold front, convergence of surface winds, uplift of warm, humid air along mountain slopes

a tornado-like cloud that remains aloft and does not touch the Earth's surface is called a

funnel clouds

if you are indoors when a tornado approaches, the best precaution is to:

go to the basement and get under a sturdy bench

a squall line usually forms...

in the mT air along or ahead of a cold front

weather watch

indicated when hazardous weather is possible based on current or anticipated atmospheric conditions. the actual occurrence or timing of the hazardous weather is uncertain. people do not need to interrupt their normal activities except to remain alert for threatening weather and to keep the TV or radio on

Cumulus Stage

initial stage - cumulus clouds build vertically and laterally over 15 minutes and surge upward; at the same time, other clouds merge; cumulus clouds are products of convection within the atmosphere contains primarily updrafts as the cumuliform cloud develops vertically due to unstable atmospheric donations and some type of trigger mechanism

the base of the cumulonimbus cloud

is approximately the convective condensation level (CCL)

a gust front

is caused by the downdraft of a mature thunderstorm, resembles a mini cold front, may induce development of secondary thunderstorm cells, is associated with a mature thunderstorm

a downburst

is designated a microbus or macroburst depending on the distance imp aced along the ground

wind shear

is the change in horizontal wind speed or direction with increasing altitude - weak vertical wind shear favors short-lived updrafts, low cloud tops and weak thunderstorms. whereas strong vertical wind shear favors vigorous updrafts and severe thunderstorms

what is lightning?Â

lightning represents an electrical discharge, occurring when sufficient electrostatic charges build between distant points in the atmosphere causing a "flash-over" as atmosphere's resistance finally breaks down. lightning can be observed between positively and negatively charged regions.Â

what hazards are accompanied by thunderstorms?

lightning, downbursts, flash-flood-producing rain events, large hail and on occasion tornadoesÂ

funnel cloud

localized lowering of cloud base into a tapered column of water droplets

shelf cloud

low elongated cloud that is wedge-shaped with a flat base - appears at the edge of a gust front and beneath and attached to a cumulonimbus cloud - thought to develop as a consequence of uplift of stable warm and humid air along the gust front - damaging surface winds may occur, associated with severe thunderstorm

a globular-type cloud found on the underside of an anvil of a cumulonimbus cloud is:

mammatus

updrafts occur alongside downdrafts during the _____ stage of the life of a thunderstorm cell.

mature

violent weather (hail, tornadoes) is most likely to occur during the _____ stage of the life cycle of a thunderstorm cell.

mature

thunderstorm

mesoscale weather system; product of vigorous convection that extends deep into the troposphere, sometimes reaching the tropopause or even higher, upward during air currents are made visible by billowing cauliflower shaped cumuliform clouds; consists of one or more convection cells

During spring over North America, the general progression of tornado occurrence is

northward

flash flooding is possible when persistent heavy rains fall

on frozen ground, on soils already saturated with water, in mountainous terrain

hail is most frequent

on the high plans east of the rockies

Mature Stage

precipitation reaches earth's surface; stage lasts for 15-30 min, rain, ice pellets, and snow descend the cloud and drag the adjacent air downward, creating a strong downdraft (exits base of cloud and relatively cool) alongside the updraft contains both updrafts and downdrafts as precipitation initially reaches the ground and lightning-producing electrical activity peaks - the frictional drag on the heavy precipitation produces downdraft through the cell

the most important force operating in a tornado is (the)

pressure gradient force

the visible phase of the lightning stroke is called

return stroke

what are the recommended tornado safety rules?

seek shelter, avoid shelters that have wide, free-span roofs, interior hallway/basement, stay clear of windows, lie flat on the floor with your head covered

what are the recommended safety rules you should observe to protect yourself and your property from lightning?Â

seek shelter, don't shower/cook/use telephone

which one of the following cloud types may be accompanied by strong surface winds? stratus, cirrus, roll cloud, shelf cloud

shelf cloud

A waterspout usually is ______ a tornado.

smaller than

Tornadoes are most likely to occur in the ______ sector of an intense midlatitude cyclone

southeast

The troposphere is normally less stable in

spring than fall

dissipating stage

subsiding air replaces the updraft throughout the cloud, effectively cutting off the supply of moisture provided by the updraft. adiabatic compression warms the subsiding air, the relative humidity drops, precipitation tapers off and ends, and convective clouds gradually vaporize the updraft has essentially disappeared and the downdrafts predominate until both the precipitation and lightning activity dwindle in the cell

dart leaders

surges of negative electrical charge that follow the conductive path formed by the initial stepped leaders and return stroke of a lightning bolt

multicell clusters

that form the mesoscale convective complexes consist of a series of cells moving along as a single unit. these large circular clusters of thunderstorms develop into a long-lived complex with characteristics mesoscale dimension clusters and form one of the most common thunderstorm types. since the updrafts often become strong, these clusters provide a moderate threat for severe weather

why is a tilted updraft important to the development of especially severe and long-lasting thunderstorms?

the great the altitude of the top of a thunderstorm, the more likely it is that the system will produce severe weather

gust front (mature stage)

the leading edge o a mass of relatively cool gusty air that flows out of the base of a thunderstorm cloud (downdraft) and spread along the ground well in advance of the parent thunderstorm cell; a mesoscale cold front

return stroke

the return stroke follows the path of least resistance and often emanates from tall, pointed structures such as a metal flagpole or tower.Â

appearance of a flat anvil top indicates that the cumulonimbus cloud has reached

the tropopause

End of mature stage

thunderstorm cell attains max intensity toward end - rain is heaviest, lightning bolts are most numerous and hail, strong surface winds and even tornadoes may develop,Â

cumulonimbusÂ

thunderstorm cloud that forms as a consequence of deep convection in the atmosphere

what areas of the US experience the most tornadoes annually?

tornado alley - a corridor stretching from eastern TX and the TX panhandle northward through OK, KS, and portions of Nebraska Central OK has the highest annual incidence of tornadoes

free convection

triggered by intense solar heating of the earth's surface - not sufficiently energetic enough to generate a thunderstorm

supercell

typically has a single intense updraft and nearly always produces significant severe weather. a mesocyclone, a precursor of a tornado, is often present

single cell

typically these cells are weak, short-lived and poorly organized. since the updrafts are weak, most single-cell thunderstorms provide only a slight threat for becoming severe

entrainment (mature stage)

unsaturated air at the edge of the cloud is down into the cloud - continues throughout the life cycle of a thunderstorm cell -entrained air mixes with the cloudy (saturated) air causing some of the water droplets and ice crystals to vaporize - the consequent evaporative cooling weakens the buoyant uplift and strengthens the downdraft

stepped leaders

a breaching path and produce a narrow ionized channel. when a branch of the stepped leaders comes within about 00 m of the ground, it is met by a positively changed return stroke from the ground.

convection

vertical air circulation in which cool air sinks and forces warm air to rise

why do some thunderstorms cells surge to great altitudes and trigger severe weather, while others do not?

vertical wind shear - weak vertical wind shear - the flow of warm humid air into the cell is weak, the downdrafts outflow pushes the gust front well ahead eventually cutting off the supply of humid air, precipitation falls through and thereby weeks the updraft

the most destructive aspect of tornadoes in terms of property damage is

very strong winds, an abrupt drop in air pressure, subsidiary vortices

typically, of all the tornadoes that occur each year in the US, most are rated as ____ on the F-scale

weak

why is a tilted updraft important to the development of especially severe and long-lasting thunderstorms?

when a thunderstorm updraft is tilted by vertical wind shear, precipitation does not fall against (and thereby weaken) the updraft. the thunderstorm cell can billow upward to great altitudes and perhaps become severe. permits the updraft to continue supplying the thunderstorm cell with warm. humid air without the self-limiting interference caused by the downdraft. usually a thunderstorm can become severe with a tilted updraft if certain synoptic scale weather conditions are favorable