Ch 5
Which environmental lapse rate represents the most unstable condition in a layer of unsaturated air?
11°C per 1000 m
supercooled droplet
A cloud composed of liquid droplets at temperatures below 0°C (32°F). When the cloud is on the ground it is called supercooled fog or cold fog.
standard rain gauge
A nonrecording rain gauge with an 8-inch diameter collector funnel and a tube that amplifies rainfall by tenfold.
ice-crystal (Bergeron) process
A process that produces precipitation. The process involves tiny ice crystals in a supercooled cloud growing larger at the expense of the surrounding liquid droplets. Also called the Bergeron process.
adiabatic process
A process that takes place without a transfer of heat between the system (such as an air parcel) and its surroundings. In an adiabatic process, compression always results in warming, and expansion results in cooling.
Doppler radar
A radar that determines the velocity of falling precipitation either toward or away from the radar unit by taking into account the Doppler shift.
blizzard
A severe weather condition characterized by low temperatures and strong winds (greater than 35 mi/hr) bearing a great amount of snow either falling or blowing. When these conditions continue after the falling snow has ended, it is termed a ground blizzard.
snow
A solid form of precipitation composed of ice crystals in complex hexagonal form.
black ice
A thin sheet of ice that appears relatively dark and may form as supercooled droplets, drizzle, or light rain come in contact with a road surface that is below freezing. Also, thin dark-appearing ice that forms on freshwater or saltwater ponds, or lakes.
sleet
A type of precipitation consisting of transparent pellets of ice 5 mm or less in diameter. Same as ice pellets.
rime
A white or milky granular deposit of ice formed by the rapid freezing of supercooled water drops as they come in contact with an object in below-freezing air.
ice storm
A winter storm characterized by a substantial amount of precipitation in the form of freezing rain, freezing drizzle, or sleet.
trace of precipitation
An amount of precipitation less than 0.01 in. (0.025 cm).
absolutely unstable atmosphere
An atmospheric condition that exists when the environmental lapse rate is greater than the dry adiabatic rate. This results in a lifted parcel of air being warmer than the air around it.
conditionally unstable atmosphere
An atmospheric condition that exists when the environmental lapse rate is less than the dry adiabatic rate but greater than the moist adiabatic rate. Also called conditional instability.
absolutely stable atmosphere
An atmospheric condition that exists when the environmental lapse rate is less than the moist adiabatic rate. This results in a lifted parcel of air being colder than the air around it.
radar
An electronic instrument used to detect objects (such as falling precipitation) by their ability to reflect and scatter microwaves back to a receiver. (See also Doppler radar.)
snow squall
An intermittent heavy shower of snow that greatly reduces visibility.
precipitation
Any form of water particles—liquid or solid—that falls from the atmosphere and reaches the ground.
fallstreaks
Falling ice crystals that evaporate before reaching the ground.
ice nuclei
Particles that act as nuclei for the formation of ice crystals in the atmosphere.
rain
Precipitation in the form of liquid water drops that have diameters greater than that of drizzle.
shower (rain)
Precipitation in the form of liquid water drops that have diameters greater than that of drizzle.
snow grains
Precipitation in the form of very small, opaque grains of ice. The solid equivalent of drizzle.
virga
Precipitation that falls from a cloud but evaporates before reaching the ground. (See Fall streaks.)
freezing rain (glaze)
Rain or drizzle that falls in liquid form and then freezes upon striking a cold object or ground. Both can produce a coating of ice on objects, which is called glaze.
drizzle
Small water drops between 0.2 and 0.5 mm in diameter that fall slowly and reduce visibility more than light rain.
Why is snow challenging to measure?
Snow accumulations vary greatly from one spot to the next.
water equivalent
The depth of water that would result from the melting of a snow sample. Typically about 10 inches of snow will melt to 1 inch of water, producing a water equivalent of 10 to 1.
accretion
The growth of a precipitation particle by the collision of an ice crystal or snowflake with a supercooled liquid droplet that freezes upon impact.
cloud seeding
The introduction of artificial substances (usually silver iodide or dry ice) into a cloud for the purpose of either modifying its development or increasing its precipitation.
orographic uplift
The lifting of air over a topographic barrier. Clouds that form in this lifting process are called orographic clouds.
coalescence
The merging of cloud droplets into a single larger droplet.
thundersnow
The occurrence of thunder and lightning while snow is falling, typically as part of an intense midlatitude winter storm.
condensation level
The process by which water vapor becomes a liquid.
collision-coalescence process
The process of producing precipitation by liquid particles (cloud droplets and raindrops) colliding and joining (coalescing).
moist adiabatic rate
The rate of change of temperature in a rising or descending saturated air parcel. The rate of cooling or warming varies but a common value of 6°C per 1000 m (3.3°F per 1000 ft) is used.
dry adiabatic rate
The rate of change of temperature in a rising or descending unsaturated air parcel. The rate of adiabatic cooling or warming is about 10°C per 1000 m (5.5°F per 1000 ft).
environmental lapse rate
The rate of decrease of air temperature with elevation. It is most often measured with a radiosonde.
rain shadow
The region on the leeside of a mountain where the precipitation is noticeably less than on the windward side.
hailstones
Transparent or partially opaque particles of ice that range in size from that of a pea to that of golf balls.
snow pellets
White, opaque, approximately round ice particles between 2 and 5 mm in diameter that form in a cloud either from the sticking together of ice crystals or from the process of accretion. Also called graupel.
If a rising, unsaturated air parcel is colder and heavier than the air surrounding at all levels, the atmosphere is ____.
absolutely stable
The atmosphere is _____ when a lifted parcel of air is colder and heavier than the air surrounding it.
absolutely stable
Suppose the rising air parcel is warmer and less dense than the air around it. In this case, the atmosphere is ____.
absolutely unstable
When a parcel of air expands and cools, or compresses and warms, with no interchange of heat with its outside surroundings, this situation is called a(n) _____ process.
adiabatic
A parcel of air expands and cools, or compresses and warms, with no interchange of heat with its outside surroundings. What is this called?
adiabatic process
With radar, the brightness of the echo is directly related to the _____ of rain falling in the cloud.
amount
Radar gathers information about precipitation in clouds by measuring the ____.
amount of energy reflected back to a transmitter
Most rain at middle latitudes is produced by the ice crystal process. This is because ____.
clouds in these regions can extend into regions where air temperatures are below freezing
In clouds with tops warmer than -15 °C (5 °F), the _____ process can play a significant role in producing precipitation.
collision coalescence
The elevation above the surface where a cloud first forms is called the ____.
condensation level
The elevation above the surface where the cloud first forms is called the _____.
condensation level
A _____ atmosphere exists when a parcel of air can be lifted to a level where it becomes saturated, a cloud forms, and the rising parcel becomes warmer than the air surrounding it.
conditionally unstable
The first mechanism that can cause the air to rise is _____.
convection
These two conditions, working together, will make the atmosphere the most stable:
cool the surface and warm the air aloft
Which set of conditions, working together, will make the atmosphere the most stable?
cooling the surface and warming the air aloft
Hail forms inside this cloud:
cumulonimbus
Suppose rain falls on one side of a street and not on the other side. This rain most likely fell from a ____ cloud.
cumulonimbus
Which cloud type would be most likely to form in an unstable atmosphere?
cumulonimbus
The most common snowflake form is ____.
dendrite
The _____ is the rate at which the air temperature surrounding us decreases as we climb upward into the atmosphere.
environmental lapse rate
Ice crystals and snowflakes falling from high cirrus clouds are called _____.
fallstreak
Ice crystals and snowflakes falling from high cirrus clouds are called _____.
fallstreaks
In the winter, you read in the newspaper that a large section of the Midwest is without power due to downed power lines. Which form of precipitation would most likely produce this situation?
freeing rain
In a conditionally unstable atmosphere, the environmental lapse rate will be ____ than the moist adiabatic rate and ____ than the dry adiabatic rate.
greater; less
The combination of drifting and blowing snow, after falling snow has ended, is called a _____.
ground blizzard
The _____ process of rain formation proposes that both ice crystals and liquid cloud droplets are present in clouds at temperatures below freezing.
ice-crystal
Aircraft icing would be heaviest and most severe ____ freezing temperatures.
in a cloud at just below
The moist adiabatic rate is different from the dry adiabatic rate because:
latent heat is released inside a parcel of rising saturated air
Rising saturated air cools at a lesser rate than rising unsaturated air primarily because:
latent heat of condensation is released in a rising parcel of saturated air
The largest snowflakes would probably be observed in ____ air whose temperature is ____ freezing.
moist; near
Orographic clouds form ____.
on the windward slope of a mountain
Doppler radar normally displays the heaviest rainfall rates in these colors:
orange and red
Subsidence inversions are best developed in high pressure areas because the ____ air associated with them causes the air to ____.
sinking; warm
ubsidence inversions are best developed in high pressure areas because the ____ air associated with them causes the air to ____.
sinking; warm
A raindrop that freezes before reaching the ground is called ____.
sleet
Which below best describes the shape of a large falling raindrop about 5 millimeters in diameter?
slightly elongated and flattened on the bottom
A conditionally unstable atmosphere is ____ with respect to unsaturated air and ____ with respect to saturated air.
stable; unstable
A _____ consists of a funnel-shaped collector attached to a long measuring tube.
standard rain gauge
Which cloud type would most likely form in absolutely stable air?
stratus
Which of the following is not a way of producing clouds?
subsidence
Water droplets existing at temperatures below freezing are referred to as _____ droplets.
supercooled
The ice crystal process of precipitation formation operates in the mixed ice and water region of a cold cloud where there are ice crystals and ____.
supercooled droplets
The dry adiabatic rate is the rate at which ____.
temperature changes in a rising or descending parcel of unsaturated air
Which of the following is not considered an important factor in the production of rain by the collision-coalescence process?
the number of ice crystals in the cloud
A hot "bubble" of air that breaks away from the warm surface and rises, expanding and cooling as it ascends, is known as a(n) _____.
thermal
Which cloud type will only produce precipitation by the collision-coalescence process?
thick, warm cumulus clouds
If you observe large raindrops hitting the ground, you could conclude that the cloud overhead was ____ and had ____ updrafts.
thick; strong
If an air parcel is given a small push upward and it continues to move upward on its own accord, the atmosphere is said to be ____.
unstable
These two conditions, working together, will make the atmosphere the most unstable:
warm the surface, cool the air aloft
What set of conditions, working together, will make the atmosphere the most unstable?
warming the surface and cooling the air aloft