1. Stability

3. Figure 5.2

4. pressure vs. height pressure is a force per unit area
pressure at sea level is around 1000 millibars
pressure decreases with height exponentially
50% of the mass of Earth’s atmosphere is below an altitude of 5-6 km (the 500 millibar height)

5. adiabatic temperature change

6. Figure 5.3

7. lifting mechanisms

8. orographic lifting

9. frontal wedging

10. convergence

11. 3-d storm

12. convection over the Florida peninsula

13. convection

14. Figure 5.4

15. Figure 5.5

16. wet and dry adiabatic temperature change

17. absolute stability

18. absolute instability

19. conditional instability

20. Table 5.1 Summary of categories of atmospheric layer stability
Environmental lapse rate (ELR) Stability
ELR > 10C/km Unstable
6C/km < ELR < 10C/km Conditionally unstable
(Unstable if saturated,
stable if unsaturated)
ELR < 6C/km Stable
ELR = 10C/km Neutral if unsaturated,
unstable if saturated
ELR = 6C/km Neutral if saturated,
stable if unsaturated

21. environment < dry

22. environment > dry

23. dry < environment < dry

24. Figure 5B

25. Table 5.2
Table Stability categories and likelihood of severe convective storms for various ranges of the Lifted Index (LI), Showalter Index (SI), Convective Available Potential Energy (CAPE), Total Totals (TT) index and SWEAT index.
Stability LI SI CAPE TT SWEAT
Very stable > +3
(no significant activity)
Stable to > < 0
(Showers possible;
isolated T’showers unlikely)
Marginally unstable 2 to to to to 50
(T’showers possible)
Moderately unstable 4 to – 3 to to to to 300
(Thunderstorms possible)
Very unstable 6 to – 6 to – to to to 400
(Severe T’storms possible)
Extremely unstable <  <  > > 400
(Severe T’storms probable;
tornadoes possible)