Dense Fog — Grapevine, California

2025-12-03 · Grapevine, California

Event narrative

CHP reports dense fog on the Grapevine portion of I-5.

Wider weather episode

High pressure aloft with an inversion layer persisted since the last week of November. Low temperatures dipped into the mid 30s at times when the low clouds cleared in the Central Valley. Otherwise, low temperatures were only slightly cooler when the low clouds, rather than fog, lingered. Patchy dense fog occurred at times during the first five days of the month in the San Joaquin Valley, but lifted to a stratus deck for the next few days. Dense fog was prevalent in the foothill areas, including the Grapevine, the Sierra Nevada foothills, and the coastal ranges at elevations between 1,000 feet and 2,500 feet from the 1st until the 9th.

Elsewhere, seasonably cool temperatures were recorded while dry conditions were present, such as in the mountains above 2,500 feet and the Kern County desert. Freezing overnight low temperatures were reported in the desert during the first several days of the month, which is common during December.

Fog and low stratus cloud cover continued over the San Joaquin Valley, as well as the lower Sierra Nevada foothills and coastal ranges up to around 2,500 feet for much of the second week of the month. However, dense fog became most prevalent in the San Joaquin Valley each night and morning from the 12th until the 15th. Most locations in the valley observed dense fog, even when they did not observe any clearing during the daytime on the 12th until the 15th. Enough moisture remained trapped in the Central Valley while the inversion layer served as a lid over the mountains and foothills due to the stagnant high pressure pattern in place.

Source: NOAA Storm Events Database, event_id 1304886. Narrative written by the NWS forecast office that issued the report.