Weather & Climate Exam 3

Fog

• A cloud with its base at or very close to the ground surface

• The same as a cloud but different method and plan of formation

• Forms by cooling or additional of water vapor

Fog formed by cooling

• Radiation fog

• Advection fog

• Upslope fog

Fog formed by the addition of water vapor

• Steam fog

• Frontal fog

Radiation Fog

• Results from rapid cooling of the ground which causes surrounding air to cool to its dew point and condensation occurs

  • Nighttime phenomena with clear skies and high relative humidity

  • Early morning phenomena that dissipates with sunrise (which warms ground and decreases humidity)

  • Found downslope in hilly terrain

Advection Fog

• Warm, moist air blown over a cold surface. This chills the air to its dew point and fog forms (thick)

  • Need winds to provide turbulence

  • Common in summer/fall along west coast

Upslope Fog

• Humid air moves upslope and cools adiabatically

• Forms when dew point reached

Steam Fog

• Occurs when cool air moves over warm water and moisture evaporates from the water

  • Common over lakes and rivers

  • Fall phenomena on clear, crisp mornings

  • Winter phenomena when arctic air blows over warm ocean currents

Frontal / Precipitation Fog

Warm air lifts over cold air which produces clouds. When the cold air below is near the dew point and rain evaporates, fog is produced.

Dew

Condensation of water vapor on objects that have radiated sufficient heat to lower temperatures to the dew point of surrounding air

Frost

Forms when dew points is below freezing and water vapor changes directly from the gas to solid phase without entering liquid state (deposition) (not frozen dew)

Sleet

Frozen rain drops

Graupel

Snow pellets with no crystalline shape

Rime

Water droplets in fog freeze on cold surfaces

Ice-Crystal (Bergeron) Process

• Temperature is below 0

• Super cooled water droplets sublimate to ice, forming snowflakes

• Most precipitation in mid latitudes

Collision-Coalescense Process

• Large water droplets function as condensation nuclei

• Most tropical precipitation

Virga

Small raindrops that evaporate while falling through dry air

Air Mass

• Large body of air characterized by a homogenous temperature and moisture content

• Loses original identity as it moves from its source region

Air Mas 2 Letter Code

• 1st letter (lower case)

  • m (maritime; humid; water source)

  • c (continental; dry; land source)

• 2nd letter (upper case)

  • P (polar)

  • A (artic)

  • T (tropical)

• Cold front is collision of mT and cP

Front

• Boundaries that separate air masses of different densities

• Greater difference in air masses → more severe weather

• Move west → east

Changes caused by passage of a front

• Temperature

• Humidity

• Pressure

• Speed/direction

• Cloud cover

Cold Front

Warm Front

Stationary Front

Occluded Front

faster, steeper, cold

• Cold fronts move ___ than warm fronts

• The frontal boundary of a cold front is ____ relative to a warm front

• Usually more severe storms associate with a ___ front

Cold Front Weather

• Air pressure drops

• Cloudiness increases

  • cirrus, cumulus, cumulonimbus

• May have severe storms

• Temperature and humidity drop

Warm Front Weather

• Air pressure drops

• Cloudiness increases

  • cirrus, altostratus, nimbostratus

• Temperature and humidity increases

Stationary Front

Develops when a front shows no appreciable movement

2 Conditions of Stationary Fronts

• Momentum equal

• Barrier

Momentum Equal (stationary front)

• Cold air mass is far enough south that it loses its identity

• Warm air mass is far enough north that it loses its identity

Barrier (stationary front)

• Mountain ranges may prevent an advancing front from moving

• Cloudiness and precipitation occurs for several days

Occluded Front

• Cold front overtakes a warm front

  • Cold occlusion - air behind the moving occluded front is colder than the air ahead

  • Warm occlusion - air behind the moving occluded front is warmer than the air ahead

• Overcast skies and periods of rain and snow

• Commonly associated with latter stage of frontal cyclones (hurricanes)

Cyclogenesis

• Develops at boundary between cold polar air and warm subtropical air

• Upper air flow causes cyclonic surface conditions

• Difficult to predict more than a week in advance

Nor’easters

• Cyclonic storms that affect the East Coast from October-April

• Low pressure system forms in Gulf of Mexico

• Upper air jet stream’s trough carries system up East Coast

• Very difficult to predict

Nor’easters Impacts

• Massive precipitation

• High winds

• Large waves and storm surge

• Airports shut down and power outages

Hurricane

• Most destructive natural disaster on Earth

• Steep pressure gradient generates inward spiral and draws in warm, moist air

• Fueled by release of latent heat when huge quantities of water vapor condense

Eye Wall

Hurricane’s greatest wind and heaviest rain

Eye

• Center of the hurricane

• Air descends, precipitation and winds slow/cease

Formation of a Hurricane

• Tropical Disturbance - moves with trade winds, low pressure

• Tropical Depression - low pressure drops, faster winds

• Tropical Storm - pressure continues to drop

• Hurricane - winds greater than 119 kph

Saffir-Simpson Index

Ranks intensity of a hurricane on a scale of 1 to 5

Storm Surge

Wind Damage

Tornado

• Violently rotating column of air usually in contact with the base of a cumulonimbus cloud and the ground

• Associated with cold fronts, spring, mid-latitudes

• Spiral counter-clockwise in Northern Hemisphere

Mesocyclone

• Rotating column of air in a cumulonimbus cloud

• Early stage of a tornado

• “Comma shape” called hook echo

Doppler Radar

• Can detect rotation of mesocyclones

• Radar emits radio waves that reflect off raindrops in a cloud

Fujita Intensity Scale

Measures tornado intensity from F0 - F5

Lightning

• Highly visible form of energy transfer

Mature Thunderstorm

Warm updrafts and cold downdrafts function as polarization mechanisms; electrical charge separation

Moonbow