Case Study 013"Southern California Floods and Florida Tornadoes"
23 February 1998
A closed upper low over the eastern Pacific Ocean, off the northern California coast at 12Z on the 23rd, progressed slowly southeastward with the upper low passing across Southern California on the 24th (Fig. 3). A subtropical moisture connection, with values exceeding 0.75 inch, was directed into Southern California from the southwest. Divergence associated with the right rear entrance region to a 120 knot upper jet streak helped to enhance large-scale lift over Southern California from 12Z on the 23rd through 00Z on the 24th. From 00Z to 12Z on the 24th, the axis of subtropical moisture and zone of enhanced large-scale lift associated with the jet streak moved eastward to a position along the lower Colorado River Valley. This synoptic pattern resulted in strong orographic upslope flow along the south-facing slopes in Southern California.
The storm system that hit Florida brought three supercells that produced tornadoes in central Florida between 03 and 07 UTC on 23 February. These storms formed ahead of a frontal boundary as it intersected an outflow boundary left over from convection earlier in the day. Strong wind shear developed as a low level jet formed beneath a strong subtropical jet and aided in the development of the supercells.
The damages and deaths in Central Florida made this one of the Significant Weather Events of 1998.