Convective and shear parameters associated with northern and central California tornadoes during the period 1990–1994

This is a study of the shear and buoyancy parameters associated with thirty tornadic thunderstorms that occurred in northern and central California during the period 1990-1994. A set of convective and rotational environmental parameters, obtained from proximity soundings, is calculated for each event. This sample is then stratified into two categories, F0 and F1-F2, based upon statistically significant differences found in the analyses of the low-level shear parameters. The majority of the parent thunderstorms formed in a relatively low-buoyancy environment, asConvective Available Potential Energy (CAPE) values did not vary significantly across the data sample. In addition, CAPE is found not to be descriminator of tornado damage rating, with no statistically significant difference in buoyancy values between the F0 and F1-F2 case groupings. The 0-1km positive shear is found to be a highly statistically signficant descriminator between the F0 and F1-F2 case groupings. Lower layer positive shear and lower layer storm-relative helicity values for approximately two-thirds of the total cases are in ranges that suggest the parent thunderstorms were probably supercells. More importantly, the 0-2km positive shear and the 0-3km storm relative helicity estimates for about all of the F1-F2 tornadoes are in a range of values documented to support mesoscyclone formation. For both groups, most of the positive shear is found to occur approximately in the SFC-850mb layer, with the region of positive buoyancy generally confined to below 500mb. These results are consistent with observations for low-topped supercells documented in other studies. Composite temperature/dewpoint profiles and hodographs are constructed to provide a prototype buoyancy/shear environment for both of the case groupings: (a) mixed non-supercellular and supercellular (F0); and, (b) likely supercellular (F1-F2).