1. Case Study in Conditional Symmetric Instability
METR 4433: Mesoscale Meteorology Spring 2008 Semester Dr. Kelvin Droegemeier School of Meteorology University of Oklahoma

3. Definition and Attributes of CSI
The combined effects of gravitational and inertial forces leading to instability of a parcel displaced in a slantwise direction
Conditional refers to an atmosphere near saturation
The slantwise displacement resulting from the instability restores the atmosphere to neutrality
Banded precipitation often results from CSI owing to the fact that the longitudinal instability occurs (i.e., rolls aligned with the shear or thermal wind)
Bands typically range from km wide and from km long (slopes of 1:100)
Typically last 1-3 hours and remain stationary
Vertical velocities can be 10 m/s

6. Characteristics of CSI
Occurs in regions where vertical wind profile shows increasing speed and veering with height (10-20 m/s over 1-2 km)
Occurs in the presence of low static stability in the middle troposphere and a stable air mass in the boundary-layer (north of a surface frontal boundary)
Occurs near a warm front and ahead of an upper-level trough
Occurs where the slope of the isentropes (theta-e or s) are steeper (more vertical) than the isopleths of absolute momentum (M)

8. Note weak shortwave approaching area

9. Shortwave reflected at sfc as inverted trough

10. Atmosphere nearly saturated (good for CSI) with strong low-level inversion

11. NEXRAD VAD from Sterling, VA – note wind veering with height and increasing in speed

12. CSI often occurs in regions of frontogenesis and FG reinforces the slantwise circulation and helps take it to smaller scales

13. mb thickness

14. CSI occurred between D-C, where strong stability is present – and thus convection would not occur!