Fronts

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

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

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.

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

Fronts http://www.youtube.com/watch?v=vPC5i6w3yDI