Mid-Latitude Cyclones and Associated Fronts

Overview

• Mid-latitude cyclones are low-pressure systems forming and moving in mid-latitudes, making them extratropical.
• Associated with various fronts that bring different weather conditions.
• Circulate counterclockwise in the Northern Hemisphere.

Types of Fronts

Cold Fronts

• Weather Effects: Heavy intense precipitation, hail, thunder, lightning, damaging winds, tornadoes.
• Advancement: When cold air advances into a warmer air mass.
• Cloud Formation: Tall cumulus clouds due to vertical movement.
• Precipitation: Occurs along the cold front boundary.

Warm Fronts

• Weather Effects: Sleet, freezing rain, fog.
• Advancement: Warm air advancing, overruns cooler air due to lower density.
• Cloud Formation: Stratus clouds, causing light drizzly precipitation ahead of the front line.
• Wind Patterns: Southerly winds behind, easterly winds ahead.

Occluded Fronts

• Form when a cold front catches up to a warm front.
• Causes extreme lifting, leading to intense weather.
• Marks the end of the cyclone as air masses mix.

Stationary Fronts

• Initial stage of mid-latitude cyclones where neither air mass is advancing.

Cyclogenesis

• Definition: Development or strengthening of a mid-latitude cyclone.
• Starts with a stationary front and forms a kink as a frontal wave.
• Upper-level divergence strengthens low pressure.
• Cyclones dissipate within a few days.

Source Regions

• Lee-side Lows: Develop on the leeward side of the Rockies and Appalachians.
• Cape Hatteras, NC: Major source, influenced by warm Gulf Stream waters.

Nor'easters

• Mid-latitude cyclones along the U.S. East Coast.
• Begin as Hatteras low-pressure systems, affected by cold air damming.
• Weather Effects: Rain, sleet, freezing rain, snow depending on temperature.
• Known for intensity and rapid development, increasing their danger.

Key Concepts

• Fronts: Boundaries between different air masses.
• Winds and Movement: Westerly winds behind cold fronts; counterclockwise circulation around low pressure.
• Weather Intensity: Varies with front type and cyclone stage; occlusion often marks peak intensity.