NATS 101 Lecture 24 Mid-Latitude Cyclones

Cyclone Evolution

Cyclone Family

Decaying Situation

Where Winds are Divergent

What Increases Divergence?

What Increases Divergence?

What Increases Divergence?

Longwaves and Shortwaves

Longwaves and Shortwaves

Vertical Structure

	Cyclone deepens only if divergence in column exceeds convergence
	System tilts toward the west with height
	Tilt would align upper-level (UL) divergence over the surface low
	Results in low deepening

Storm of Century

Storm of Century

Storm of Century (not shown)

Storm of Century

Track of Storm of Century

Cyclone-Anticyclone Tracks

Summary: Extratropical Cyclones

	In mid-latitudes, much of our weather is associated with the Extratropical Cyclone
	Cyclone denotes the circulation around a low pressure center
	Their circulation affects an area of 1000 km (or more) across, through entire troposphere

Summary: Extratropical Cyclones

	ET cyclones derive their energy from horizontal temperature contrasts.
	Not surprisingly, they generally form on a boundary between a warm and cold air mass, near the jet stream axis
	They transport warm air poleward and upward, and cold air equatorward and downward.

Summary: Extratropical Cyclones

	They tend to follow a similar lifecycle
	They form underneath areas of UL divergence, downwind of SW troughs
	The low pressure center tends to move with speed and direction of 500 mb flow
	They enhance temperature contrasts into frontal zones, which act as a breeding ground for future ET cyclones

Next Lecture

	Topic – Forecasting Part I
	Reading - Ahrens pg 231-248
	Problems - 9. 3, 9.4, 9.5, 9.6