The Fronts and Backs of Weather 4 Air Masses –similar characteristic of temperature, moisture centers of high pressure –acquire characteristic of source region needs uniform surface (mountain regions - no good) 4 Four Basic Source Regions –Maritime (m) versus Continents (c) –Polar (P) versus Tropical (T)

The Fronts and Back of Weather 4 Continental Air Mass low moisture content few clouds –Winter (cP) Very cold, dry Temperature varies much within air mass Active weather at edge –Summer (cT) Very hot Associated with drought limited source - NA 4 Maritime Air Mass high moisture content abundant clouds –Winter (mP) Chilly, damp Temperature varies some within air mass Active weather at edge –Summer (mT) Hot and humid Associated with HHH abundant source - NA

The Fronts and Back of Weather 4 Fronts (low pressure zones) –valleys between domes of air masses separate air masses of different density –density differences due to Temperature, Moisture »biggest difference: mT (hot, humid) & cP (cold, dry) Many weather parameters vary across a front –Temp, Moisture, Pressure, Wind, Clouds, Precipitation –front type is totally dependent on winds in the colder (more dense) air mass winds blow toward boundary - cold front winds blow away from boundary - warm front

The Fronts and Back of Weather 4 Cold Fronts –denser air moving toward the boundary –Temperature highest at the front, then falls off –Most active weather with front (T-storms) Steep slope to front –RH rises, Visibility up, Pressure rises –mT to cP - common 4 Warm Fronts –denser air retreating from the boundary –Temperature rises as front approaches then steady after front –Most active weather precedes the front Gentle slope to front –RH steady, Visibility down, Pressure drops –cP to mT - common

The Fronts and Back of Weather 4 Stationary Front –winds in denser air mass blow parallel to front –unsettled weather - mainly on cold side –breeding ground for cyclone development 4 Speed of front –determined by surface winds in colder air mass –overrunning determined by speed of winds in the warmer air mass