Mid-Latitude Depressions

Question 1

What is a mid-latitude depression?

Answer 1

Low pressure weather system caused by meeting of polar and tropical maritime air masses at polar front

Question 2

The passing of a depression follows a 3 stage model:

Answer 2

1) Embryo
2) Maturity
3) Decay

Question 3

Outline embryo stage of depression

Answer 3

• TM air meets cooler, denser PM air
• Convergence results in spiral movement as PM air forces TM air upwards, twisting a result of Earth’s movement
• Rising air decreases pressure behind warm front, rising air removed by strong upper atmosphere winds
• Moves in NE direction due to southwesterlies and Coriolis effect

Question 4

Outline mature stage of depression

Answer 4

• Pressure continues to decrease as air rises at warm front over cold air
• Rising air reaches ‘dew point’ increasing temps, due to saturation and formation of clouds = Precipitation
• Precipitation decreases within warm sector due to increase in temp and decrease in uplift
• Cold front, steep gradient formed by rapid undercutting
• Warm TM air rises due to undercutting of PM air, cumulonimbus clouds develop = Heavy rainfall
• Cold front approaches, wind speeds increase due to increasing pressure gradient
• Wind speeds increase as cold front passes, then decreases in cold sector

Question 5

Outline decay stage of depression

Answer 5

• Cold front moves faster than warm front
• Cold front catches up with warm front, lifting warm air from ground (Occluded front)
• No TM air at surface
• Depression infills with cold air, precipitation decreases, pressure increases and wind speeds drop

Question 6

What weather is associated with a warm front?

Answer 6

• Precipitation: Continuos drizzle
• Cloud: Nimbostratus
• Wind direction: SW
• Wind speed: Increase
• Temp: Remains stable

Question 7

What weather is associated with a warm sector?

Answer 7

• Precipitation: Isolated shower at most
• Cloud: Stratus
• Wind direction: Changing from NW to SW
• Wind speed: Low
• Temp: 4-6°C increase

Question 8

What weather is associated with a cold front?

Answer 8

• Precipitation: Heavy rainfall
• Cloud: Cumulonimbus
• Wind direction: NW
• Wind speed: Increase
• Temp: Remains stable