1. Severe Weather Some Meteorology Basics

2. Atmospheric Heating  Atmosphere is heated from the bottom  Solar energy absorbed by the Earth is re- radiated as heat  Warm air is less dense so it rises  This mixing of the air produces our weather

3. Atmospheric Heating is Uneven  Latitude (position relative to the poles and the equater) influences amount of solar energy received  Land re-radiates heat much faster than water  Moisture also plays a role –Evaporation requires energy –Condensation releases energy

4. Uneven Heating and Air Pressure  Areas where air is heated  Air becomes less dense (weighs less)  Air rises  Combination is measured as Low Pressure

5. Uneven Heating and Air Pressure  Areas where air is less heated  Air becomes more dense (weighs more)  Air sinks  Combination is measured as High Pressure

6. Air Pressure and Weather  Low Pressure areas have rising air  Air rises to areas where it is cooler  Cooling may produce condensation  Condensation may result in precipitation  Lows are generally associated with stormy weather

7. Air Pressure and Weather  High Pressure areas have sinking air  Air sinks to areas where it is warmer  As air is heated, it can hold more moisture  If more moisture is not available, the effect is that the air become drier (less humid)  Highs are generally associated with clear weather

8. Air Pressure and Wind  Warm air rises in areas of Low Pressure  Cool air sinks in areas of High Pressure  To equalize the pressure, air must move from areas of High Pressure to areas of Low Pressure  This movement of air is called wind

9. Simple, but not so simple  Air moves from areas of high pressure (sinking) to areas of low pressure (rising)  However, the air doesn’t follow a straight path  Because the Earth spins on its axis, the wind is “deflected” in a slightly different direction

10. Coriolis Effect  The “deflection” of the wind, or any moving object, because of the Earth’s rotation is known as the Coriolis Effect  In the Northern Hemisphere, moving objects are deflected to the right of their intended path

11. Highs, Lows and Around It Goes  Wind blows from High Pressure toward Low Pressure  We can also think of this as blowing “outward” or away from the High  And, “inward” or toward the Low  The Coriolis Effect deflects these winds, so…

12. Highs, Lows and Around It Goes  Winds blow clockwise and out from Highs  Winds blow counterclockwise and in toward Lows

13. Counterclockwise winds around a Low: Hurricane Fran

14. Counterclockwise winds around a Low: “The Perfect Storm”

15. Low Pressure and Severe Weather  Air rises, cools and may promote condensation in Lows  Lows are generally associated with stormy weather  Some storms are quite severe

16. Examples of Severe Weather and Low Pressure Systems  Tropical Depressions (Lows)  Tropical Storms (Stronger Lows)  Hurricanes (Very Strong Lows)  Mid-Latitude Cyclones (Strong Lows with associated warm and cold fronts)  Nor’easters (Strong Lows that move off the East Coast  Tornadoes (Small, powerful Lows associated with fronts)