Standard Grade WeatherStandard Grade WeatherDepressionsDepressions

Today we are going to learn..Today we are going to learn..

What a depression isWhat a depression is The main features of a depressionThe main features of a depression The weather associated with a depressionThe weather associated with a depression

What is it?What is it?

Depressions are areas of Depressions are areas of lowlow pressure pressure which bring rain, cloud, wind and unsettled which bring rain, cloud, wind and unsettled conditionsconditions

They form when warm, tropical air from They form when warm, tropical air from the south meets cold, polar air from the the south meets cold, polar air from the northnorth

The boundary between the two air masses The boundary between the two air masses is called a is called a frontfront

They are shown on synoptic chartsThey are shown on synoptic charts

A DepressionA Depression

isobars

Isobars close together =

strong winds

Winds flow in anticlockwise direction

Low pressure = < 1000 mb

High pressure = > 1000 mb

Main featuresMain features

When the two air masses meet the lighter, warm When the two air masses meet the lighter, warm air is forced to rise above the denser, cold air air is forced to rise above the denser, cold air forming forming frontsfronts

As the warm air rises it cools, water vapour As the warm air rises it cools, water vapour condenses, forms cloud and then condenses, forms cloud and then frontal rainfrontal rain

Where the cold front travels faster than the warm Where the cold front travels faster than the warm front and catches up, an front and catches up, an occludedoccluded front is front is formedformed

Depressions travel from west to east across the Depressions travel from west to east across the UKUK

Depressions move from West to East

Warm sector

What have we learnt so far?What have we learnt so far?

Always moves west to east

COLD AIR

WARM AIR

Winds blow anticlockwise

WARM SECTOR

COLD FRONT WARM FRONT

OCCLUDED FRONT

This is a Low Pressure System, commonly known as a Depression

TASK: Add labels TASK: Add labels to your diagram of to your diagram of

a depressiona depression

Cold sectorCold sector

Cold sectorCold sector

Isobars are close together

Air pressure is below 1000mb

TasksTasks

Depressions are very ______ areas of Depressions are very ______ areas of ____ pressure. They bring _________ ____ pressure. They bring _________ weather. On ________ weather maps weather. On ________ weather maps they are represented by upside down they are represented by upside down ____. They form when _______ air rises ____. They form when _______ air rises over ______ air. A typical depression over ______ air. A typical depression passes over the UK from _____ to passes over the UK from _____ to _______. _______.

COLD LOW WEST LARGE V’SUNSETTLED EAST WARM SYNOPTIC

What is the weather like?What is the weather like?

OCCLUDED FRONT

Cold sectorCold sector

Weather fair but beginning to cloud over as warm front approaches. Temperatures cool

WARM FRONT

Brings cloud, steady rainfall and strong wind. Temperatures rise

WARM SECTOR

Slight drizzle as skies clear and rain stops. Temperatures still warm

COLD FRONT

Heavy rainfall, thick cloud cover, strong winds and lower temperature.

Cold sectorCold sector

Skies clear as rain stops. Wind lessens. Temperature remains cool

What is the weather like?What is the weather like?

As the warm front approaches it brings steady As the warm front approaches it brings steady rainfall, low cloud and strong windsrainfall, low cloud and strong winds

In the warm sector the temperature rises, the In the warm sector the temperature rises, the cloud breaks and winds drop, often a small cloud breaks and winds drop, often a small period of dry weatherperiod of dry weather

As the cold front approaches, winds can become As the cold front approaches, winds can become gale force, temps drop and rain becomes very gale force, temps drop and rain becomes very heavyheavy

As the depression passes, rain eases and As the depression passes, rain eases and winds, although cold, begin to dropwinds, although cold, begin to drop

Warm sector

Prolonged, steady rain

Heavy rainHeavy showers

with sunny intervals

Drizzle/fair Sunny/fair

EASTWEST

Occluded FrontsOccluded Fronts What is it?What is it? Occluded fronts Occluded fronts

happen when the happen when the cold front travels cold front travels faster than the warm faster than the warm front and overtakes front and overtakes it.it.

Weather?Weather? Strong winds, Strong winds,

storms, thick cloud storms, thick cloud and rainand rain

TASK: Write a definition for occluded TASK: Write a definition for occluded front, don’t forget to draw the symbol.front, don’t forget to draw the symbol.

TasksTasks2. Use page 80 of new key geography 2. Use page 80 of new key geography

GCSE to draw the GCSE to draw the diagram of a cross-diagram of a cross-sectionsection of a depression. Add labels and of a depression. Add labels and colour it in.colour it in.

4. Collect a copy of ‘4. Collect a copy of ‘What happens When a What happens When a Depression Passes over Musselburgh?’Depression Passes over Musselburgh?’ Use the following slides to help you write Use the following slides to help you write a description of the weather in a description of the weather in Musselburgh at each stage.Musselburgh at each stage.

Glue it into your jotter.Glue it into your jotter.

What happens when a depression What happens when a depression passes over Musselburgh?passes over Musselburgh?

Temperatures are Temperatures are coolcool because Musselburgh is in the because Musselburgh is in the cold sector of the depression. cold sector of the depression. CloudsClouds are beginning to form. are beginning to form. Winds blow from the Winds blow from the SouthSouth west.west.

Temperatures Temperatures riserise as warm as warm front arrives. It is now front arrives. It is now rainingraining heavily as the warm front is heavily as the warm front is over Musselburgh. Winds are over Musselburgh. Winds are blowing from the blowing from the westwest..

Temperatures are Temperatures are coolcool because because Musselburgh is in the cold sector of Musselburgh is in the cold sector of the depression. the depression. Skies are clearingSkies are clearing. . Winds blowing from the Winds blowing from the north.north.

Temperatures are Temperatures are cooling downcooling down as the cold front arrives. It is as the cold front arrives. It is now now rainingraining heavily because heavily because cold front over Musselburgh. cold front over Musselburgh. Winds blowing from Winds blowing from north west.north west.

Temperatures are Temperatures are warmwarm as as Musselburgh is in the warm sector Musselburgh is in the warm sector of the depression. Weather is of the depression. Weather is dry,dry, winds are blowing from the winds are blowing from the westwest

Tasks:Tasks:

Collect a copy of the Collect a copy of the air pressureair pressure past past paper questions from the front. Answer paper questions from the front. Answer the questions in your jotter.the questions in your jotter.

Look through your notes to help you Look through your notes to help you answer the questions.answer the questions.