Upslope flow behind the departing trough banked up against the Tehachapi Mountains during the evening of December 17 producing areas of dense fog which impacted travel along the major passes for a few hours. Visibility was reduced to a few hundred feet in the Grapevine area where California Highway Patrol paced traffic for nearly four hours on Interstate 5.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS HNX wrote it up.
Upslope flow behind the departing trough banked up against the Tehachapi Mountains during the evening of December 17 producing areas of dense fog which impacted travel along the major passes for a few hours. Visibility was reduced to a few hundred feet in the Grapevine area where California Highway Patrol paced traffic for nearly four hours on Interstate 5. The fog lifted into a stratus deck around midnight on December 18 and visibility along the passes rapidly improved.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Hanford, CA wrote its last area forecast discussion before the first event at Dec 17, 5:45 PM PST, 2 hours 28 minutes earlier.
Area Forecast Discussion National Weather Service San Joaquin Valley - Hanford CA 545 PM PST Mon Dec 17 2018 ...Updated Air Quality Section... .SYNOPSIS... Skies will gradually clear this evening and overnight as the cold front moves east of the area. Some lingering clouds, patchy dense fog, and showers are possible over the Tehachapi Mountains through Tuesday morning. High pressure will build over the U.S. West Coast during Tuesday through Thursday, and dry weather is expected. Patchy night and morning fog is possible in the San Joaquin Valley through the middle of the week. && .DISCUSSION...A few light showers remain over the the Sierra Nevada, including at North Fork and Bass Lake. However, most of the precipitation has ended as the cold front has passed over much of Central California, so have cancelled the Winter Weather Advisory for the Sierra Nevada from Yosemite to Kings Canyon NP. Locations in the high country of the Sierra Nevada reported a few inches of snow, including four inches at Tuolumne Meadows as of this morning. Skies have been clearing over the west side of the San Joaquin Valley, based on latest satellite data. With the upper- level trough now over the region, winds have increased over the east side of the Kern County mountains, as a few locations are reporting gusts around 50 mph. Expect coverage to spread into the desert, while gusts further increase towards the evening, so will let the Wind Advisory continue this afternoon through late tonight. The northwest flow aloft will likely allow increased low cloud cover to persist this evening into Tuesday morning over the west and north facing slopes of the Sierra foothills and the Tehachapi Mountains. In addition, some patchy fog is possible in the San Joaquin Valley tonight through Tuesday morning, especially in areas that received the greatest rainfall with this recent system and have already cleared, such as Merced and Los Banos. Some locations in these areas and into the Sierra foothills towards Mariposa reported just above one inch of rain, especially during last night/early this morning. High pressure will build over Central California and much of the Western U.S. during Tuesday through Thursday, so dry conditions are expected for much of the region. More widespread fog in the Central Valley is possible by Tuesday night into Wednesday. Another low pressure system will pass over mainly Northern California during Thursday night into Friday, although some light precipitation is possible the northern portion of our forecast areas, or around Merced/Los Banos and east towards Yosemite. Otherwise, a zonal, or westerly flow, will dominate the weather pattern during the weekend. Another low pressure system is possible by Sunday afternoon through next Monday, although it appears to follow a similar trajectory, while the brunt of the moisture moves over Northern California and the Pacific Northwest. While the latest model solutions are generally in decent agreement, much uncertainty remains for the extended period (especially Friday through next Monday). More details will soon follow. && .AVIATION... In the San Joaquin Valley tonight, areas of MVFR conditions are possible due to haze and mist after 03z. Localized areas of IFR conditions are also possible after 07z due to reduced visibilities from fog and mist. Otherwise VFR conditions will prevail over the next 24 hours. && .AIR QUALITY ISSUES... None. && .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is low. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information an/or to provide feedback. && .HNX Watches/Warnings/Advisories... Wind Advisory until 1 AM PST Tuesday CAZ095-098-099. && public...BSO avn/fw...Bollenbacher synopsis...BSO weather.gov/hanford
1 dense fog. Local standard time, as filed.
California Highway Patrol reported dense fog along Interstate 5 between Fort Tejon and Gorman and paced traffic for approximately four hours.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, December 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 789826.