Dense Fog — W Central S.j. Valley, California

2008-11-23 to 2008-11-24 · W Central S.j. Valley, California

Wider weather episode

The high pressure ridge that brought record temperatures to the central and southern San Joaquin Valley at mid-month also evaporated moisture from the soil. With moisture in the lowest levels of the airmass over the Valley floor, conditions were primed for dense Tule Fog development. As the high-pressure ridge continued to strengthen, fog development was mostly inhibited as the lowest levels of the airmass dried out. As the ridge began to weaken and temperatures cooled, humidities over the Valley floor began to increase again, and the airmass began cooling to near saturation overnight. Dense fog developed near Visalia during the evening of November 21st and became widespread through much of the Valley by daybreak on the 22nd. Dense fog redeveloped during the nights of the 22nd-23rd, and continued well into late morning. This scenario was repeated the next night as well, before an approaching upper-level trough further weakened the ridge and brought enough mixing to inhibit fog development. Visibility reports of only a few hundred feet were common during these dense fog events, from both automated weather stations throughout the valley as well as Highway Patrol pacing reports. The dense fog conditions during the early morning of the 24th brought several car accidents in the Fresno area. One accident resulted in one fatality in the Elkhorn area.

Source: NOAA Storm Events Database, event_id 143311. Narrative written by the NWS forecast office that issued the report.