"Southern California Severe Weather"
02 September 1998

On 2 September 1998, a series of strong thunderstorms affected Southern California, bringing strong winds, lightning and heavy rains. The winds knocked down power lines and trees across the area, while the heavy rains resulted in widespread flash flooding across the valley. In addition, a funnel cloud was reported by a helicopter pilot near Pomona, CA.

A mid-level ridge off the west coast of the U.S. dominated the flow aloft over California. The result was flow from the south and east, bringing in moisture all the way from the Gulf of Mexico, and spreading moisture northward from Hurricane Isis. At 1200Z 2 September, the GOES-10 Water Vapor shows mid-level moisture entering the southern California region from the east. By 1800Z, the moisture had worked its way in. This moisture at mid-levels can be noted in RUC analysis sounding from 1800Z for Los Angeles. Analysis of this sounding using the lowest 100 mb, one can estimate a LCL of 800 mb, and a LFC of about 660 mb. With these found, the parcel can be estimated and generous positive area results above 660 mb. The lift needed to initiate these storms would be convergence at the surface along the mountain ridges. Most, if not all, of the storms formed as a result of orographic lift, which can be seen when comparing the US 2km Nowrad image of the storms with the topography of California. The rather high-based nature of many of these storms was instrumental in producing wind at the surface, and even generating reports of microbursts in the area.

Damages were generally minor, with initial reports of about $50,000 in a report from Kern County. Lightning strikes also started several wildfires, the largest fire consumed 1,500 acres of grass east of Bakersfield.

Case Study 41