Met 8 - Low Pressure Systems - Depressions

What is a front?

A boundary between two different air masses

What is a depression?

An area of low pressure

What direction does a warm front move?

Warm air replaces cold air

What direction does a cold front move?

Cold air replaces warm air

What is the polar front?

The boundary between cold polar maritime air and warm tropical maritime air

What is the average slope of a warm front?

1:150

What is the average slope of a cold front?

1:50

How far ahead of the surface front can cirrus clouds appear in a warm front?

Up to 500 NM (925 km)

What type of clouds are common ahead of a warm front?

Cirrus, altostratus, and nimbostratus

What weather is associated with a warm front approach?

Thickening cloud, decreasing visibility, and light to moderate rain

What happens to pressure as a warm front approaches?

It steadily falls

What happens to temperature and dew point after a warm front passes?

Both usually increase

What happens to wind when a warm front passes?

It veers by 90° and becomes stronger and gustier

What is the typical visibility behind a warm front?

Poor, with possible drizzle and low cloud

What clouds are found in an active cold front?

Cumulus and cumulonimbus

What weather is associated with a cold front passage?

Heavy rain, squalls, possible thunder and hail

What happens to temperature and dew point after a cold front passes?

Both decrease

What happens to pressure after a cold front passes?

It rises quickly

What is frontal turbulence?

Turbulent conditions caused by sharp wind veer during cold front passage

What happens to visibility after a cold front passes?

It improves rapidly to good or excellent

What is an occluded front?

A front formed when a cold front overtakes a warm front, lifting the warm air off the ground

What are the two types of occluded fronts?

Cold occlusion and warm occlusion

What weather is associated with occluded fronts?

Mixed weather from both warm and cold fronts, often with persistent cloud and heavy rain

What is a stationary front?

A front that stops moving or moves very slowly

What weather is associated with stationary fronts?

Persistent low cloud, poor visibility, and precipitation

What is a secondary depression?

A new low that forms along an existing front of a primary depression

What is the warm sector in a depression?

The area of warm air between the warm and cold fronts

How is a depression steered?

By the upper-level jet stream

What type of air does a heat low contain?

Warm, unstable air

What type of cloud may form in a heat low?

Cumulonimbus

What is another name for a heat low?

Thermal low

What synoptic feature often follows a cold front?

A dry slot with clear skies

What indicates an active front on a synoptic chart?

A sharp 'V' in the isobars and strong wind veer

What is a trough on a weather chart?

A line of low pressure that may cause front-like weather without an air mass change