Weather Fronts

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 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 FRONT

WARM, LIGHTER AIR

COLD, DENSER AIR

SURFACE COLD FRONTS WEATHER FRONTS

USA SLP Map Obtained from AMS Datastreme WEATHER FRONTS

COLD L

COLD WARM

USA Temp Map Obtained from AMS Datastreme TYPES OF FRONTS

USA SLP Map Obtained from AMS Datastreme TYPES OF FRONTS

COLD WARM AIR AIR

USA Map Obtained from AMS Datastreme TYPES OF FRONTS

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

WARM AIR WARM FRONTS WARM FRONTS AND COLD FRONTS

• Warm air moves towards “retreating” cold air • Cold air moves towards warm air

L 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

COLD AIR L

WARM AIR Animation courtesy of Dr. Joby Hilliker EXTRA-TROPICAL CYCLONES TRACKS OF WINTER ETCs

Alberta Clipper

Noreaster EXTRA-TROPICAL CYCLONES EXTRA-TROPICAL CYCLONES

Northeast winds over New England

- Cold air - moisture from the Atlantic - SNOWFALL

L 79 PRESIDENT’S DAY BLIZZARD 79 PRESIDENT’S DAY BLIZZARD

Southeast winds becoming Northeast over New England

- Cold air - moisture from the Atlantic - SNOWFALL Storm L Track BLIZZARD OF 1978 BLIZZARD OF 1978

Northeast winds over New England

- Cold air - moisture from the Atlantic - SNOWFALL L MARCH 1993 SUPERSTORM MARCH 1993 SUPERSTORM – STORM OF THE CENTURY

Storm Track L 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 Very strong cold front

- Severe Thunderstorms formed ahead of it MARCH 1993 SUPERSTORM – STORM OF THE CENTURY

Storm Track

Storm tracked too close L 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