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 L USA SLP Map Obtained from AMS Datastreme WEATHER FRONTS COLD L COLD WARM USA Temp Map Obtained from AMS Datastreme TYPES OF FRONTS L USA SLP Map Obtained from AMS Datastreme TYPES OF FRONTS L COLD WARM AIR AIR USA Map Obtained from AMS Datastreme TYPES OF FRONTS L 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 L 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 .