1. Fronts

2. Warm Air Front Warm air replaces cold air
warm air mass=higher temperature=lesser density
Rainfall increases as the
front approaches

4. Characteristics Weather phenomenon Prior to the Passing of the Front
While the Front is Passing
After the Passing of the Front
Temperature
Cool
Warming suddenly
Warmer, then leveling off
Atmospheric pressure
Decreasing steadily
Leveling off
Slight rise followed by a decrease
Winds
South to southeast (Backing)(northern hemisphere)
North to northeast (Veering)(southern hemisphere)
Variable
South to southwest (Veering)(northern hemisphere)
North to northwest (Backing)(southern hemisphere)
Precipitation
Showers, snow, sleet, or drizzle
Light drizzle
Usually none, sometimes light rain or showers
Clouds
cirrus, cirrostratus, altostratus, nimbostratus, then stratus (pilots use the acronym CCANS) and fog; occasionally cumulonimbus in summer
Stratus, sometimes cumulonimbus
Clearing with scattered stratus, sometimes scattered cumulonimbus
Visibility
Poor
Poor, but improving
Fair in haze
Dew Point
Steady rise
Steady
Rise, then steady

5. Cold Air Front http://www.youtube.com/watch?v=xdgqkc2YJ1Q
Cooler and denser air wedges under the less-dense warmer air, lifting it
Upward motion causes lowered pressure along the cold front
Cold fronts can move up to twice as fast as warm fronts and can produce sharper changes in weather.
Since cold air is denser than warm air, it rapidly replaces the warm air preceding the boundary.
Cold fronts are usually associated with low-pressure areas.

7. Characteristics Weather phenomenon Prior to the Passing of the Front
While the Front is Passing
After the Passing of the Front
Temperature
Warm
Cooling suddenly
Steadily cooling
Atmospheric pressure
Decreasing steadily
Lowest, then sudden increase
Increasing steadily
Winds
Southwest to southeast (northern hemisphere)
Northwest to northeast (southern hemisphere)
Gusty; shifting
North to west, usually northwest (northern hemisphere)
South to west, usually southwest (southern hemisphere)
Precipitation/ conditions*
Brief showers
Thunderstorms, sometimes severe
Showers, followed by clearing
Clouds*
Increasing: Cirrus, cirrostratus, and cumulonimbus
Cumulonimbus
Cumulus
Visibility*
Fair to poor in haze
Poor, but improving
Good, except in showers
Dew Point
High; steady
Sudden drop
Falling

8. Fronts