GHY 104 1st Edition Lecture 17Weather- Weather - the short-term, day-to-day condition of the atmosphere- A “snap-shot”- Important element to weather: Temperature Air Pressure Relative Humidity Wind speed and direction Seasonal Factors- Climate – long-term average (over decades) of weather conditions & extreme in a regionAir Masses- Air Mass: Homogeneous body of air with similar temperature and moisture properties to underlying land area- Source region: Location from which an air mass originates- Classify air masses by:- Moisture – These can be either Maritime (m) = moist or continental ( c) = dry- Temperature – These can be Equatorial (E), tropical (T), polar (P), Arctic (A), or Antarctic (AA).- Know combinations of these letters and what each means for each type of air mass: cP, cT, cA and cAA, mT, mP cP – Continental Polar cT – continental Tropical cA – continental Arctic cAA – continental Antarctic  mT – maritime TropicalThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. mP – maritime Polar- As air masses migrate from source regions, temperature and moisture characteristics change andtake on characteristics of the land over which they pass. - An example of Air Mass Modification is Lake Effect SnowAtmospheric Lifting Mechanisms- Convergent Lifting- Air coming together, no place to go but up - Convectional Lifting- Uneven heating of the Earth’s surface - Orographic Lifting- Forcing over a mountain barrier- Frontal Lifting (cold and warm fronts)- Air masses collidingOrographic Uplift- Air forced over mountain on Windward slope cools at the Dry Adiabatic Rate- Once Ta lowered to Tdp = saturation, condensation at the Lifting Condensation Level = clouds.- Air continues to rise over mountain, cooling now at the Moist Adiabatic Rate- Once peak is reached, air then descends the leeward slope, warming at the DAR.- Dry hot leeward winds are called chinook winds.- Large dry area on leeward side of mountains is called the rainshadow. Frontal Uplift- Front – the leading edge of an attacking air mass - Fronts are named after the attacking air mass- Cold Fronts- Cold air is denser, heavier- Cold air forces warm air aloft- Relatively narrow, but up to 400 km wide (250 mi)- Blue triangles on a weather map- Warm Fronts- Warm air moves up and over cold air - 1000 km wide (600 mi)Red or orange half circles on a weather