1. Forecast parameters, Tornadogensis, maintenance and decay
Terrance Seddon
11/27/07

2. Over view Forecast Parameters Tornadogenesis, Maintenance and decay
Bulk Richardson Number
Mean Shear
Storm Relative Helicity
Tornadogenesis, Maintenance and decay
Type I
Type II

3. Forecast Parameter

4. Bulk Richardson Number
BRN was found to be successful in predicting conditions where storm splitting and super cell formation is likely
This is most likely due to the sensitivity to surface-inflow winds and including the 0-6km winds
V = density weighted mean winds for 0-6km and 0-.5 km

5. Mean Shear This parameter helps predict storm type.
Storms are predicted to be tornadic if CAPE and mean shear are large
However mean shear fails in practice because it is ill defined for fractal hodographs.

6. Storm Relative Helicity
Useful for predicting if the updraft will rotate cyclonically or ant cyclonically as a whole

7. Other parameters
A number very similar to BRN can be obtained by CAPE/SRH, however this number is not that useful.
More useful is CAPE X SRH, which is proportional to the energy-helicity index.

8. The Next Step
So far the parameters we have discuss will only predict the formation of supercells and mesocyclones aloft
The next step is predicting a persistent low-level mesocyclone, which is much more difficult.
The factors that have to be considered:
Precipitation distribution
Balance between SRH and low level mixing ratio
DCAPE

9. Tornadogenesis, maintenance and decay
Mesocyclonic or type I tornadoes
Nonmesocyclonic or type II tornadoes

10. Type I Tornadoes Persistent low level convergence (10-15 min)
Convergence in the boundary layer of the mesocyclone
“Seed” vertical vorticity already present near the ground.