Exam 3

Consider the accompanying figure. At which of the four positions would you expect to hear the following 12hour forecast? "Cloudy and cold this morning with snow this afternoon and tonight?"

1

Consider the accompanying figure. At which of the four positions would you expect to hear the following 12hour forecast? "Partly cloudy and continued warm through this afternoon and evening?

2

Consider the accompanying figure. At which of the four positions would you expect to hear the following 12hour forecast? "Cloudy with possible showers today, turning colder by tonight"

3

If you see lightning and hear the thunder 15 seconds later, then the lightning stroke is about ____ miles away

3

The general area where a tornado is likely to form can often be predicted up to ____ days in advance

3

Probability forecasts use climatological data that are typically averaged over ___ years

30

Consider the accompanying figure. At which of the four positions would you expect to hear the following 12hour forecast? "Clearing and colder today with continued rising pressures"

4

Beyond about ____, computer prog forecast accuracy falls off rapidly due to the chaotic nature of the atmosphere.

7 days

atmospheric model

A mathematical model consisting of many equations that describe how atmospheric temperature, pressure, winds, and moisture will change with time

c​ontinental polar (cP)

Air masses that are cold and dry and form over land

c​ontinental arctic (cA)

Air masses that are extremely cold and dry and form over land

​continental tropical (cT)

Air masses that are hot and dry, and are responsible for heat waves of summer in the western half of the United States

When caught in a thunderstorm in an open field, what action is best to take?

Crouch down as low as possible while minimizing contact with the ground.

Which instrument measures the speed at which precipitation is moving toward or away from an antenna?

Doppler radar

Most computer models produce forecasts for only one grid point.

False

The greatest annual number of thunderstorms in the United States occurs in ___

Florida

What is the origin of the cP and cA air masses that enter the United States

Northern Canada and Alaska

As the electric potential near the ground increases during a thunderstorm, a positive charge current can move up pointed objects, such as masts of ships, producing a luminous halo or glow known as ___

St. Elmo's fire

What would you expect to observe during the passage of a gust front?

Temperatures will drop and winds will become strong and gusty

Which statement about tornadoes is correct

The United States has more tornadoes than any other country in the world.

What is the most accurate description of the principle of a lightning rod?

The lightning rod intercepts the lightning and safely carries the lightning current around the object it protects

What does it mean when meteorologists say a model is "parameterized"?

The model is approximated for broad areas instead of being predicted for specific points.

A weather watch would most likely be issued for which condition?

There is a chance for tornadoes today

A small thunderstorm cloud blowing dust at the ground could warn of a severe hazard to aircraft. Why?

This could indicate an intense downdraft or microburst

A forecaster will use a prognostic chart for guidance in preparing a forecast, but will also rely on personal experience and a knowledge of local features that can affect the weather.

True

A weather forecast that predicts that future weather will be the same as present weather is called ___

a persistence forecast

Low-pressure areas tend to ____ before occluding and ____ after occluding

accelerate; decelerate

A forecast method that compares past weather maps and weather patterns to those of the present is a(n) __

analogue method

Cold fronts that move into the United States from the east, or northeast, are called ____ fronts

back door

A high pressure system that tends to persist in the same geographic location for many days is referred to as a ____ high

blocking

A stationary front does not move because winds on both sides of the front ___

blow parallel to the front and in opposite directions

The coldest of all air masses is ___

cA

Record breaking low temperatures are associated with which air mass

cP

What type of air mass would be responsible for hot, dry summer weather in southern Arizona

cT

Which air mass forms over North America only in summer?

cT

Smaller grid spacing ____ the resolution of computer forecasting models.

can increase

Suppose that where you live is typically several degrees warmer in the middle of January than the rest of the month. If you forecast this "January thaw" for the middle of next January, you would have made a ___

climatological forecast

Squall lines most often form ahead of a(n) ____ front

cold

One would expect a cP air mass to be __

cold and dry

What type of weather front would be responsible for the following weather forecast? "Increasing cloudiness and warm today with the possibility of showers by this evening. Turning much colder tonight with southwesterly winds becoming gusty and shifting to the northwest."

cold front

Cyclogenesis occurs frequently on the eastern slopes of the Rockies as a result of __

compressional heating

Developing low pressure areas generally have ____ air near the surface and ____ air aloft

converging; diverging

The initial stage of an ordinary cell thunderstorm is the ____ stage

cumulus

When upper-level divergence of air above a surface low exceeds the surface convergence of air, the surface air pressure will ____ and the storm itself will ___

decrease; intensify

Beneath an intense thunderstorm, the downdraft may become localized so that it hits the ground and spreads horizontally in a radial burst of wind. This is called a(n) ___

downburst

The air pressure normally ____ before a cold front passes and ____ after a cold front passes.

drops; rises

The typical path of a winter mid-latitude cyclone is ___

eastward or northeastward

The forecasting technique that produces several versions of a forecast model, each beginning with slightly different weather information to reflect errors in the measurements, is called ____ forecasting

ensemble

The downdraft in an ordinary cell thunderstorm is created mainly by ___

evaporating raindrops that make the air cold and heavy

Because it is located at middle latitudes, the United States is only rarely affected by polar and tropical air masses.

false

During a cold winter in which the Great Lakes are entirely covered by ice, lake-effect snows would be expected in extremely high frequencies and intensities.

false

Even if distinctive features that might indicate a tornado are observed on radar, a tornado must be observed visually before a tornado warning is issued.

false

Geographical features on the earth, such as mountain ranges, do not have much effect on the weather because the features are small compared to the thickness of the atmosphere

false

Most cloud-to-ground lightning flashes consist of a single return stroke

false

Source regions for air masses tend to be generally flat or of varied composition, and in an area of light winds dominated by surface high pressure

false

Stable atmospheric conditions usually result in good visibility

false

Weather charts and maps are still plotted and analyzed entirely by hand

false

Continental polar air associated with a wintertime high pressure area will likely bring ___

freezing temperatures

A tornado cloud that does not touch the ground is called a ___

funnel cloud

What is the best source region for an air mass?

generally flat areas of uniform composition with light surface winds

For a surface low to develop into a major storm system, the upper-level divergence of air must be ____ surface convergence of air.

greater than

The leading edge of a thunderstorm's cold outflowing air is known as a __

gust front

A weather warning indicates that __

hazardous weather is either imminent or actually occurring within the specified forecast area

The so-called Tornado Belt, or Tornado Alley, of the United States is located __

in the Central Plains

Surface pressure systems tend to move ____ the wind at the 500-mb level.

in the same direction as

A downslope wind coming off a mountain will ____ in a nearby city affected by a strong polar high-pressure system.

increase the temperature

A supercell storm is a(n) __

intense long-lasting thunderstorm with a single violently rotating updraft

Generally, the average speed of a warm front ____ the average speed of a cold front

is slower than

When a cold front passes, the lowest pressure reading at a station will occur ____ the front passes

just as

The forecast funnel outlines the steps used by forecasters to steer their attention from ____ scales and from ____ time frames

large to smaller; short to longer

Lake-effect snows are best developed around the Great Lakes during ___

late fall and early winter when cold, dry polar air moves over the relatively warm water

Most tornadoes have winds that are __

less than 125 knots

Large-scale computer models would typically have ____ grid spacing compared to small-scale models.

longer

During the winter, an air mass that moves into coastal sections of Oregon and Washington from the northwest would most likely be __

mP

What type of air mass would be responsible for daily afternoon thunderstorms along the Gulf Coast of the United States?

mT

What type of air mass would be responsible for hot, muggy summer weather in the eastern half of the United States?

mT

An accurate forecast __

may or may not show skill

What weather system can grow to be as much as 1000 times larger in area than an ordinary cell thunderstorm, even large enough to cover an entire state

mesoscale convective complex

A chart that plots how air temperature has changed over the past five days at a given station is a(n) __

meteogram

A relatively narrow downburst, less than four kilometers wide, is called a __

microburst

The signal detected by a Doppler radar is a ___

microwave reflected by precipitation

Forecasting large-scale weather events several days in advance is ___

more accurate than forecasting the precise evolution and movement of small-scale, short-lived weather systems

Many flash floods, including those that occurred over parts of New England and the mid-Atlantic states during June 2006 and in Colorado's Big Thompson Canyon in July 1976, are the result of thunderstorms that ___

move slowly

Mid-latitude cyclonic storms are better developed in the United States during the coldest months because the polar jet stream ___

moves farther south in the winter

A group of thunderstorms that develop next to one another, each in a different stage of development, is called a(n) ___

multicell thunderstorm

If a mid-latitude cyclonic storm has moved from the southwest toward the northeast during the past six hours, the storm is likely to move toward the ____ during the next six hours.

northeast

The storm system in the accompanying figure will apparently move toward the ___

northeast

In the polar front theory of a developing wave cyclone, the area of most intense weather is normally found to the ____ of the storm's center.

northwest

When two air masses collide at a front, one air mass may be pushed upward by the other. This is because ___

one air mass is denser than the other

Although many thousands of weather observations are taken worldwide each day, what regions still have sparse observations?

over oceans and higher latitudes

Mid-latitude cyclonic storms and fronts tend to move in a direction that __

parallels the isobars in the warm air ahead of the cold front

The least accurate forecast method of predicting the weather two days into the future during changeable weather conditions is usually the __

persistence forecast

The top of a thunderstorm is normally ____ charged, and the middle and lower parts are ____ charged

positively; negatively

Forecast models have a hard time predicting ___

precipitation

An ensemble forecast is considered robust when the ___

progs match each other fairly well

The forward progress of a warm front may be inhibited at night as a result of ___

radiational cooling

On a Doppler radar screen, a tornado might appear as a region of __

rapidly changing wind directions

During a cold occlusion, the cold front forces the warm front to __

rise off the ground

Occasionally, an elongated ominous-looking cloud forms just behind a gust front. This type of cloud, which appears to slowly spin about a horizontal axis, is called a ___

roll cloud

For a forecast to show ____, it should be better than one based solely on the current weather or the "normal" weather for a given region

skill

If a tornado is rotating in a counterclockwise direction and moving toward the northeast, the strongest winds will be on its ____ side

southeastern

Drylines typically occur in the ___

southern Great Plains of the United States

Tornadic thunderstorms that form ahead of an advancing cold front most often travel from ____

southwest to northeast

In the Northern Hemisphere, winds for a cold front travel south or ____ before passing, shift directions while passing, and then travel ____ after passing.

southwest; west or northwest

A line of thunderstorms that forms ahead of an advancing cold front is called a __

squall line

Which forecasting method assumes that weather systems will move in the same direction and at approximately the same speed as they have been moving?

steady-state (trend) forecast

With a limited number of wind observations, tight spacing of height (above sea level) contour lines on a 500-mb chart may indicate areas of ____ winds.

stronger

Low pressure systems tend to move toward the region of greatest ___

surface pressure drop

High pressure systems tend to move toward the region of greatest ____

surface pressure rise

A weather prediction for the United States based on El Niño events is an example of forecasting using ___

teleconnections

An air mass is characterized by similar properties of ____ and ____ in any horizontal direction at a given altitude.

temperature; humidity

In the United States, dryline thunderstorms are most common in __

the Great Plains

Ordinary cell thunderstorms only last about one hour and begin to dissipate when __

the downdraft spreads throughout the cloud and cuts off the updraft

You are generally safe inside an automobile during a lighting storm because ___

the metal car body will carry the lightning current around the passengers inside

A hook-shaped echo on a radar screen often indicates __

the possible presence of a tornado-producing thunderstorm

Thunder is caused by __

the rapid heating of air surrounding a lightning channel

If lows and highs aloft are directly above lows and high at the surface, ___

the surface system would dissipate

A probability forecast that calls for a "40% chance of rain" means that ___

there is a 40% chance that any random place in the forecast area will receive measurable rainfall

More tornadoes are being reported in recent decades because __

tornado-spotting technology has improved

A network of more than 100 Doppler radar units covers nearly all of the 48 contiguous United States

true

In a strong tornado, doubling the wind speed will quadruple its destructive potential

true

In some situations, individual thunderstorms may organize into a convective weather system that may be 1000 times larger than an individual storm

true

Some mid-latitude cyclones may have calm winds at their center, similar to a hurricane's "eye"

true

When the air is dry, tornadoes can remain invisible until they reach the ground and pick up dust

true

An ordinary cell thunderstorm ___

typically forms on warm, humid days

A nowcast is a weather forecast that extends for ___ (refer to q45)

usually not more than 6 hours

Doppler radar determines precipitation ____ by measuring changes in the ____ of the reflected radio wave

velocity; frequency

What type of rotating cloud develops from a funnel cloud or tornado and extends beneath a severe thunderstorm?

wall cloud

What type of weather front would be responsible for the following weather forecast? "Increasing high cloudiness and cold this morning. Clouds increasing and lowering this afternoon with a chance of snow or rain tonight. Precipitation ending tomorrow morning. Turning much warmer. Winds from the south and becoming southwesterly tomorrow."

warm front

The region of air between the cold and warm fronts of an open wave is known as the __

warm sector

Compared to an mP air mass, an mT air mass is ___

warmer and moister

A rotating column of air that is connected to a cumuliform cloud over a large body of water is a __

waterspout

Maritime air masses typically form over ____ and have _____ air

water; moist

For a surface storm system to intensify, the upper trough of low pressure must be located to the ____ of the surface low

west

The Enhanced Fujita scale pertains to the ___

wind speed of a tornado

The majority of lightning strikes occur __

within a cloud

analysis

​A final chart created by thousands of observations transmitted onto surface and upper-air charts to forecast weather patterns

prognostic chart

​A final forecast chart made by assimilating data into models repeatedly until a representation of the atmosphere at a specified future time can be made

m​aritime tropical (mT)

​Air masses are warm and humid, and are responsible for the hot, muggy weather that frequently plague the eastern United States in summer.

​maritime polar (mP)

​Air masses that are cold and moist, form over water, and are responsible for the cold, damp, and often wet weather along northeastern United States

data assimilation

​The process of integrating surface and upper-air observations of temperature , pressure, moisture, winds, and air density are fed into equations at regular intervals

numerical weather prediction

​The routine daily forecasting of weather by the computer using mathematical equations

h​eat lightning

​distant lightning that is seen but not heard on hot summer nights when the overhead sky is clear

street lightning

​forms when either the lightning flash occurs inside a cloud or intervening clouds obscure the flash

r​ibbon lightning

​forms when wind moves the ionized channel between each return stroke, causing the lightning to appear like it's hanging from the cloud

b​ead lightning

​occurs when the lightning channel breaks up, or appears to break up

f​orked lightning

​when a dart leader moving toward the ground deviates from the original path taken by the stepped ladder, appearing crooked