Exam 3 Review - EVSC 3300


  • Air Mass Classification:

    Warm air mass over cold air mass results in an UNSTABLE mass

    Cold air mass over warm air mass results in a STABLE mass

  1. Continental:

  • ARCTIC → very cold, dry stable, ice & snow

  • POLAR → cold, dry stable

  • TROPICAL → hot, dry, stable aloft; unstable surface

  1. Maritime

  • POLAR → cool, moist, unstable

  • TROPICAL → warm, moist, unusually stable

  • Fronts:

    WARM: warm (less dense) air overrides cold air (gentle precip.)

    COLD: cold dense air wedges under warm air; warm air rises

    STATIONARY: motionless, winds blow parallel to front

    DRYLINE: “dew point” front

  • Pressure Gradient Force (PGF):

    Goes from high to low pressure

    Horizontal pressure gradients produce horizontal wind

  • Thickness:

    Warm air is thicker than cold air

    Pressure decreases faster in cold air

    Low (high) heights = low (high) pressures (@ con. ht. surface)

    Height gradient force corresponds to PGF (@ con. ht. surface)

  • Surface vs. Aloft:

    SURFACE: more (less) mass above you

    ALOFT: associated with warm (cold) air

  • Circulations:

    Thermally direct: air away from warm → decrease in pressure

air into cold → increase in pressure

Land/Sea breeze: land → clockwise; sea → counterclock

Day/Night Winds: up mountain during day; down mountain at night

  • Forces At Work In Atmosphere:

    Apparent → coriolis, centrifugal

    Real → gravity, friction, PGF

    ★ Balances:

  • HYDROSTATIC: gravity + PGF

  • GEOSTROPHIC: PGF + coriolis

  • GRADIENT: PGF + coriolis + centrifugal

  • CYCLOSTROPHIC: PGF + centrifugal (tornado!)

  • SURFACE: PGF + coriolis + friction

  • Wind Direction & Geostrophic Wind on Diagrams:


  • Upper Tropospheric Flow:

  • Pressure decreases faster with height in cold compared to warm

  • Temperature differs b/t Equator and poles drives PGF aloft

  • Winds aloft; West to East jet stream


  • N. Hemisphere vs. S. Hemisphere

~ N. Hemisphere 

  • AROUND LOW PRESSURE: counterclockwise + convergent

  • AROUND HIGH PRESSURE: clockwise + divergent

~ S. Hemisphere

  • AROUND LOW PRESSURE: clockwise + convergent

  • AROUND HIGH PRESSURE: counterclockwise + divergent

  • Low Pressure System = upper divergence + temperature gradient


★ Reading a Weather Map:

H → high pressure (decent weather)

L → low pressure (cloudy/stormy)

* cold and warm fronts spikes and lattice point the direction front is moving

ISOBAR LINES CLOSE TOGETHER → big difference in pressure; strong winds

ISOBAR LINES FAR APART: air pressure is even; calm air/light breeze

* cold and warm front meeting → creates low pressure system

* high pressure interacting with low pressure → tight isobars