Chico Tornadic Supercell

September 26, 1986


California supercells remain poorly documented features. It is clear, however, that while buoyancy for California events is only weak to moderate (from about 200 J/kg to 1800 J/kg) updraft strength can be augmented by moderate to strong shear-induced (and rotation-induced) vertical pressure forces.

The "favorable" directional shear is often generated by the low level topography in certain areas (e.g., the Central Valley, some of the coastal valleys) in certain weather patterns. "Favorable" speed shear is associated with strong jet streams in the mid and upper troposphere and, in the Central Valley, a strong low-level (500 to 1500 meters above ground level) southeasterly jet. The resulting ratio of updraft to shear is often within documented ranges observed for supercells in the literature. To see a schematic representation of the sources of "favorable" low to midlevel shear in California, click here. To see a typical sounding and hodograph for a mesocyclone-induced tornado event (in this case, September 26, 1986), click here.

For an overview of tornado incidence in California see:

Blier, W. and Batten, K.A., 1994: On the incidence of tornadoes in California. WEA. FORECASTING, 9, 301-315.


 

 

Multiple Vortex Mesocyclone-Induced Tornado (F2) Near Chico, CA, September 26, 1986

Photo Courtesy WSO Redding

Braun, S.A. and J.P. Monteverdi, 1991: An investigation of a mesocyclone-induced tornado occurrence in northern California. WEA. FORECASTING, 6, 13-31.

Monteverdi, J.P. and S.A.Braun, 1988: An investigation of the 24 September 1986 "cold sector" tornado outbreak in northern California. National Weather Service Western Region Tech. Mem., NWS-203, 52 pp.

 



 

 

Multiple Vortex Mesocyclone-Induced Tornado (F2) Near Chico, CA, September 26, 1986

Photo Courtesy WSO Redding

Braun, S.A. and J.P. Monteverdi, 1991: An investigation of a mesocyclone-induced tornado occurrence in northern California. WEA. FORECASTING, 6, 13-31.

Monteverdi, J.P. and S.A.Braun, 1988: An investigation of the 24 September 1986 "cold sector" tornado outbreak in northern California. National Weather Service Western Region Tech. Mem., NWS-203, 52 pp.