Sunday, 9 January 2005
Tornado probabilities derived from Rapid Update Cycle forecast soundings
Tornado forecasting can be improved if forecasters incorporate data of the near-storm environment with radar data when considering tornado watches and warnings. To gain a better understanding of how tornado threat changes with changing environmental conditions, proximity soundings in the vicinity of supercells, derived from the Rapid Update Cycle model, were examined. These soundings were taken from the years 1999-2001 and 2003. A total of 644 supercell soundings were examined and split into three categories: nontornadic soundings (336), weakly tornadic soundings (217) and significantly tornadic soundings (91). Thermodynamic, moisture and wind shear parameters were compared against each other and contingency probability tables were produced for probabilities of any tornado and of a significant tornado.
The results of this investigation reinforce the findings of several previous proximity sounding studies. Notably, the parameter space of 0–1-km Bulk Shear versus MLLCL height was found very valuable in assessing the likelihood of a supercell producing a tornado. Also, in situations where values of MLLCL and 0–1-km Bulk Shear are favorable for tornado formation, large values of instability appear to increase the threat of significant tornado occurrence. As found in other studies, deep-layer shear does not appear to be a good indicator as to whether the environment is conducive to forming tornadic supercells.