meteorology lecture test two
be able to use a sounding to forecast the likelihood and severity of convection if it initiated
The stronger the convection and the longer a multistorm system exists, the greater the chances of the thunderstorm becoming severe
why do cumulonimbus clouds often have flat tops
because at the top of these clouds, the atmosphere is stable, but coming from the top of the cloud and going down, the atmosphere is conditionally unstable, causing the cloud to form but since right above the cloud is stable, the cloud can't form up there. Updraft encounters air that is warmer than itself and can no longer rise anymore, updraft air them spreads horizontally.
deep conditionally unstable environment
clouds are likely to develop with significant vertical development, we may see cumulus congestus, or cumulonimbus MALR<ELR<DALR (same as shallow conditionally, but more difference between)
Shallow conditionally unstable environment
clouds are likely to develop, but their vertical growth will be limited, we may see cumulus humilis, or stratocumulus MALR<ELR<DALR (same as shallow conditionally unstable, but less difference between them)
absolutely stable environment
clouds are unlikely to form ELR<MALR
what other piece of information is needed to help determine storm mode
doppler radar readings of wind speed and direction
DALR MALR
dry adiabatic lapse rate moist adiabatic lapse rate
why are moist and dry adiabatic lapse rates of cooling different
dry- an unsaturated (dry) parcel cools at a rate of 9.8 Ckm moist- a saturated parcel of air (T=Td) cools at the moist adiabatic lapse rate of about 6 Ckm. they cool at different rates due to the fact that latent heat is released in a rising parcel of saturated air.
supercell
extremely powerful, self-sustaining thunderstorm characterized by intense, rotating updrafts. Impressive storms that generate hail, damaging winds, and tornadoes.
how does national weather service define a severe thunderstorm
hail> 3/4 inch surface wind gusts> 50 knots tornado
diabatic process
heat is added ex. heating from absorption of radiation
what mainly determines air density at a given pressure
if a rising air parcel is colder than its environment, then it will be more dense (heavier), and will sink back down to its original level, meaning the air is stable because it resists upward movement. if the rising air parcel is warmer than its environment, it is less dense (lighter) than the surrounding air, and it will continue to rise until it reaches the same temperature as its environment, this is unstable air. To figure out the air's stability we need to measure the temperature of both the rising air and its environment's temp at various levels above the earth
as an air parcel rises, what will happen
it will adiabatically expand and cool
explain the difference between environmental lapse rate, dry adiabatic lapse rate, and moist adiabatic lapse rate
lapse rate- rate of temp change with height DALR- an unsaturated air parcel cooling (9.8) MALR- a saturated air parcel cooling (6) less dry than DALR, latent heat is released into the parcel and warms the parcel of air, offsetting some of the adiabatic cooling from expansion, nonlinear
why does the parcel cool at a slower rate (6 ckm) when it is saturated than at 9.8 ckm when it is saturated
moist adiabatic lapse rate is less dry. as water vapor condenses in a saturated parcel, latent heat is released into the parcel and warms the parcel of air, offsetting some of the adiabatic cooling from expansion
all thunderstorms need what 3 ingredients
moist surface air a conditionally unstable atmosphere a mechanism "trigger" that forces air to rise
know the differences and be able to identify the main severe storm modes (types) from radar or satellite images; air mass (ordinary), bow echo, squall line, supercell, mesoscale convective complex
multicell storms often form as a complex of storms, such as the squall line and the MCC
what is a multicell thunderstorm
needs a vertical wind shear so that: the storm becomes tilted so the updraft rides over the downdraft, precipitation does not fall through the updraft, it does not collapse on its-self
adiabatic process
process where the parcel temp changes due to an expansion or compression no heat is added or taken away from the parcel (different from temp)
bow echo
relatively small, bow-shaped systems of convective cells that are noted for producing long swaths of damaging winds (dereechos are just really big bow echos)
what is meant by stability
stability is the measure of the stability of the atmosphere, it happens when the env lapse rate is less than the moist/dry adiabatic lapse rate. Used to determine wether or not a parcel will sink or rise in the atmosphere at a specific altitude. we determine air stability by comparing the temperature of a rising parcel to the temperature of its surroundings.
what are some ways to either stabilize or destabilize the atmosphere
stabilize: radiational cooling (radiation inversion), cold air moving in at low levels, warm air above moving over cold ground, subsidence destabilize: cooling the air aloft (cold air advection aloft (wind blows cold air above warm air)), warming near-surface air; surface heating (insolation- late afternoon is when thunderstorms typically initiate from surface heating), warm air advected below (moving warm air in at low levels- often occurs with a low-pressure system passing through)
describe the atmospheric conditions at the surface and aloft that are necessary for the development of most supercell thunderstorms and tornadoes (include low-level wind shear's role)
supercells are developed mainly because a) the position of cold air above warm air produces a conditionally unstable atmosphere, and b) a strong vertical wind shear induces rotation. A supercell is more likely to develop when the winds aloft are strong and change direction from southerly at the surface to more westerly aloft and a low-level jet exists just above the earth's surface. The tilted nature of the storm allows new cells to form as old ones die out
what factors determine the bases of cumulus clouds, which form from riding thermals
surface temperature and dew point. 125(t-td) for celsius and 228(t-td) for fahrenheit.
what is a lapse rate
the rate of temp change with height
assessing atmospheric stability
to determine whether or not a parcel will rise or sink in the atmosphere, simply compare the parcel temp with the environment's temp at that same altitude -if tpar> tenv, it will rise (unstable) - if tpar=tenv, it won't rise or sink -if tpar<tenv, it will sink (stable)
stable air parcel
vertical motion is inhibited
unstable air parcel
vertical motion is not inhibited, it is favored rapid cloud development commonly produces cumulus and cumulonimbus clouds
if the atmosphere is conditionally unstable, what condition is necessary to bring on instability
we need the difference in temperature between the surface air and the air aloft to be relatively small. as the air aloft warms and surface air cools, it stabilizes the atmosphere. the cooling of air surface may be due to nighttime radiational cooling at the surface, an influx of cold surface air brought in by the wind (cold advection), or air moving over a cold surface. the lowering of an entire layer of air makes it more stable, so the lifting of a layer of air makes it more unstable.
what atmospheric conditions are necessary for the development of ordinary cell thunderstorms
an unstable environment, form in warm, humid air masses (mT) away from significant weather fronts (<1 hour lifetime). tend to form where warm, humid air rises in a conditionally unstable atmosphere and where vertical wind shear is weak.
how do gust fronts form and what type of changes of wind, temperature, pressure, and turbulence is associated with a gust front
Gust fronts form when rain evaporates below the LCL, cools, and creates a cold outflow. Wind changes direction and increases in strength, the temperature of the environment cools, pressure is increased, and there is strong turbulence associated with a gust front.
squall lines
Long lines of thunderstorms that form along a cold front.
how do we classify tornado strength with the enhanced fujifita scale
MPH winds, knots, and expected damage. The fujita scale classifies tornados according to their rotational wind speed.
what is the difference between a watch and a warning
when tornados are likely to form during the next few hours, a tornado watch is issued to alert the public that tornados may develop within a specific area during a certain time period. Once a tornado is spotted, either visually or on a radar screen, a tornado warning is issues to alert people of the approaching storm.
an air parcel
will rise if it is less dense than the environment will sink if it is more dense than the environment
what happens to an air parcel as it is pushed up a mountain and then descends on the other side
wind forces air up and over, the windward side will be cloudy and rainy as air ascends, the leeward side will be warmer and drier as the air descends back down, often called rain shadow (can cause a HUGE amount of rain)
Mesoscale Convective Complex
A slow-moving roughly circular cluster of interacting thunderstorm cells covering an area of thousands of square kilometers that may persist for 12 hours or more.
why does thunderstorm and tornado activity change with the seasons
Thunderstorm and tornado activity form along or just east of a boundary line called a dryline. This is a narrow zone where there is a sharp horizontal change in moisture. In the US, drylines are most frequently observed in the western half of TX, OK, and KS, and most frequently occur during spring and early summer, where they are observed about 40% of the time. The atmosphere is most stable in the early morning and most unstable in the afternoon, so that is why tornadoes and thunderstorms mostly occur in the afternoon.