WEATHER FRONTS

Map Obtained from TWC

COLD FRONTS

We already have stated that a cold front is a boundary separating two

air masses (a cold air mass and a warm air mass)

The cold air is found behind the cold front and it advances towards

the warm air

COLD FRONTS

SURFACE

COLD, DENSER AIR

WARM, LIGHTER AIR

COLD FRONT

Cold air undercuts warm air. Warm

air is pushed upwards, thus clouds form

and precipitation occurs.

This often happens ahead of cold fronts.

The greater the temp difference

between cold and warm air the greater

the upward motion – CUMULUS clouds

COLD FRONTS

WEATHER FRONTS

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USA SLP Map Obtained from AMS Datastreme

WEATHER FRONTS

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COLD

COLDW

AR

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USA Temp Map Obtained from AMS Datastreme

TYPES OF FRONTS

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USA SLP Map Obtained from AMS Datastreme

TYPES OF FRONTS

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COLD

AIR

WARM

AIR

USA Map Obtained from AMS Datastreme

TYPES OF FRONTS

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COLD FRONT

COLD AIR MOVES TOWARDS WARM AIR

USA SLP Map Obtained from AMS Datastreme

COLD FRONTS

• But cold air is denser than warm air at

equal pressure (at the surface of Earth)

• So how exactly does cold air “move”

towards warm air?

COLD FRONTS

COLD FRONTS

WARM FRONTS

• Warm air moves towards “retreating” cold air

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WARM AIR

WARM FRONTS

WARM FRONTS AND COLD

FRONTS• Warm air moves towards “retreating” cold air

• Cold air moves towards warm air

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ALL TYPES OF FRONTS

All fronts occur at the boundaries of two (or more) air masses

FRONTS & EXTRA TROPICAL

CYCLONES• Fronts, low pressure, wind direction, temperature

combined give you an idea of what an ETC is

LCOLD AIR

WARM AIR

Animation courtesy of Dr. Joby Hilliker

EXTRA-TROPICAL CYCLONES

TRACKS OF WINTER ETCs

Alberta Clipper

Noreaster

EXTRA-TROPICAL CYCLONES

EXTRA-TROPICAL CYCLONES

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Northeast winds over New England

- Cold air

- moisture from the Atlantic

- SNOWFALL

79 PRESIDENT’S DAY BLIZZARD

79 PRESIDENT’S DAY BLIZZARD

LStorm

Track

Southeast winds becoming Northeast over New England

- Cold air

- moisture from the Atlantic

- SNOWFALL

BLIZZARD OF 1978

BLIZZARD OF 1978

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Northeast winds over New England

- Cold air

- moisture from the Atlantic

- SNOWFALL

MARCH 1993 SUPERSTORM

MARCH 1993 SUPERSTORM –

STORM OF THE CENTURY

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Storm Track

Very strong cold front

- Severe Thunderstorms formed

ahead of it

Heavy Snow - North Side of the storm track

(~North winds – cold air – upwards motion)

17” record snowfall Birmingham AL

4” snowfall Atlanta GA

2ºF Birmingham AL

MARCH 1993 SUPERSTORM –

STORM OF THE CENTURY

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Storm Track

Storm tracked too close

to RI resulting in many

hours of south winds

and lots of rainfall

before the changeover

to snow

NOT A RECORD STORM

FOR RI!

THE PERFECT STORM

THE PERFECT STORM