weather forecasting and air masses 1
TRANSCRIPT
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Air Masses, Fronts and Global Wind Patterns
Meteorology
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Air MassesAir Masses
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Definition:Definition: Air mass - a large dome of air
which has similar horizontal temperature and moisture characteristics throughout.
Very similar to a balloon.
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Continental Arctic (cA): Continental Arctic (cA): • Frigid – record low temperatures• Dry - very low dew points• Dense - very high barometric pressure• Usually originate north of the Arctic Circle
Siberian Express • Usually once or twice a winter• very rarely form during the summer
because the sun warms the Arctic.
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Continental polar (cP): Continental polar (cP): • Cold and dry - stable• Usually originates in NW Territory of Canada• Influences mainly the northern USA• Responsible for clear and pleasant weather
during the summer • Usually in winter• Creates troughs in the polar jet stream• Lake effect snow in Great Lakes areas
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Maritime polar (mP):Maritime polar (mP):• Cool and moist - unstable • Originate over N. Atlantic and N. Pacific• Main Influence - the Pacific Northwest
and the Northeast. • can form any time of the year • Generally not as cold as cPcP air masses
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Maritime tropical (mT): Maritime tropical (mT): • Warm and very moist – unstable• Originate in the Gulf of Mexico and
the Southern Atlantic Ocean• Influences the eastern USA • Most prevalent during summer • Responsible for hot, humid summer
days across the South and the East.
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Continental Tropical (cT):Continental Tropical (cT): • Very Hot and very dry – stable aloft • Originates in Desert Southwest and
northern Mexico • Occurs in the summer, rarely in winter• Usually keeps the Desert Southwest
scorching above 100oF during summer• Generally clear skies, hot, low humidity
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Source RegionsSource Regions
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Reasoning for TornadoesReasoning for Tornadoes
Orographic Perfection
Meeting of• Moist - mT• Hot - cT• Cool – cP
Roc
ky M
tn.
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Tornado AlleyTornado Alley http://www.britannica.com/thunderstorms
_tornadoes/video/ocliwea124v4.mov
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Fujita ScaleFujita Scale
(NationalAtlas.com)
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Fronts and their symbolsFronts and their symbols
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Fronts:Fronts: Boundary between two air masses Characterized by shift in weather
Cold Warm Stationary Occluded
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5 Characteristics of a 5 Characteristics of a FrontFront
Sharp temperature changes over a relatively short distance.
Changes in air moisture content Shifts in wind direction Pressure changes Clouds and precipitation
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Cold FrontsCold Fronts• Temperature – drops rapidly• Pressure – rises steadily• Clouds – Vertical building• Precipitation – Heavy along front• Winds – Strong and shifting
• Typically move faster than warm front
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Cold FrontCold Front
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(Fozzy)
Cold FrontCold Front
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Cold FrontCold Front
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In the summer, cold In the summer, cold fronts can trigger:fronts can trigger:
thunderstorms large hail dangerous winds tornadoes
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Graphic Depiction!
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Warm FrontsWarm Fronts• Temperature – rises slowly• Pressure – slight rise, then fall• Clouds – strato- and cirro-• Precipitation – long, steady• Winds – variable and light
• Typically will have affect for days
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Warm FrontWarm Front
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Warm FrontWarm Front
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Warm FrontWarm Front
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Effects of warm frontsEffects of warm fronts Slow-moving warm front can mean
days of wet weather before warm air Sometimes water vapor in warm fronts
condense to producerainsnowsleet freezing rain
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Stationary FrontStationary Front
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Stationary FrontsStationary Fronts• Temperature – stagnent• Pressure – slightly fluctuates• Clouds – altocumulus• Precipitation – none• Winds – variable and light
• Can last for days weeks
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Occluded FrontOccluded Front
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Occluded FrontsOccluded Fronts• Temperature –
•Warm – gets milder•Cold – gets colder
• Pressure – •Warm - slight drop•Cold – slight rise
• Clouds – cumulus• Precipitation – steady and light• Winds – variable and light
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Occluded FrontOccluded Front
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Different Temperatures - Different Temperatures - Different Pressures Different Pressures
CoolAir
WarmAir
Denser
MorePressure
Less Dense
LessPressure
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Pressure and Air MovementPressure and Air Movement
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Pressure Gradient ForcePressure Gradient ForceDifference in pressure over a given
distance---between isobarsClose together = step pressure gradient
STRONG windsFar apart = gentle pressure gradient
Light winds• Just like contour lines
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Pressure Gradient ForcePressure Gradient Force
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Isobaric MapsIsobaric Maps
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Coriolis EffectCoriolis EffectApparent force due to the
rotation of the Earth (Think Merry-go-round)
N. Hemisphere wind turns right S. Hemisphere wind turns left
Strength depends on latitude and wind speed
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Coriolis EffectCoriolis Effect
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Coriolis EffectCoriolis Effect
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Centripetal ForceCentripetal ForceIn-ward directed forceAllows an object to remain in
circular motionWinds moving around high and
low pressure areasClockwise around Highs.Counter-clockwise around Lows.
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Friction Friction (What a Drag)(What a Drag) The resistance to movement Surface winds are affected by friction Why? Ground resistance:
trees, mountains, houses, buildings, etc. This drag causes winds to blow across
pressure gradient at the surface.
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Pressures All TogetherPressures All Together
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General Planetary CirculationGeneral Planetary Circulation
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Winds Winds Horizontal movements at
surfaceNames from WHEREWHERE it came
from…not where it is going!!!
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Around Pressure CellsAround Pressure Cells
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Pressure CellsPressure Cells High – In and Up
Converge at surfaceAscend in centerDiverge Aloft
Low – Down and OutConverge aloftDescend in centerDiverge at surface
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X-section of Planetary CirculationX-section of Planetary Circulation
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January Global Pressure Map
January
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July Global Pressure Map
July
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Summer HighsSummer Highs
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