High pressure built into California on December 18. Mainly clear skies, light winds and inversion conditions resulted in areas of dense fog forming overnight in the San Joaquin Valley.
Every event with a place to put it; 5 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
High pressure built into California on December 18. Mainly clear skies, light winds and inversion conditions resulted in areas of dense fog forming overnight in the San Joaquin Valley. The fog lifted into a low cloud deck by early afternoon and dissipated by late afternoon.
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 18, 3:40 PM PST, 11 hours 35 minutes earlier.
Area Forecast Discussion National Weather Service Hanford CA 340 PM PST Sat Dec 18 2021 .UPDATE... Updated Air Quality section. && .SYNOPSIS... A relatively cold air mass will remain in place over Central California this weekend. Outside of major urban areas, near freezing temperatures are expected in the San Joaquin Valley tonight and Sunday night. Precipitation chances will increase Tuesday night and Wednesday as a low pressure system moves southward down the coast of California. && .DISCUSSION... A ridge of high pressure will shift southward over California this weekend. Sub-freezing temperatures are expected in the Kern County desert tonight and Sunday night. Outside of major urban areas, near freezing temperatures are likely in the most of the San Joaquin Valley tonight and Sunday night. Here are probabilities of minimum temperatures of 32 degrees or lower for select locations in the San Joaquin Valley on Sunday, December 19th, 2021: Hanford 79%, Madera 73%, Delano 67%, Merced 65%, and Visalia 59%. Here are probabilities of minimum temperatures of 32 degrees or lower for select locations in the San Joaquin Valley on Monday, December 20th, 2021: Hanford 72%, Madera 58%, Merced 55%, Delano 53%, and Visalia 52%. A cyclone aloft will meander around the Eastern Pacific Ocean, at about latitude 40 North, longitude 135 West Monday and Monday night. A piece of energy should break off from this upper-level cyclone and move toward the California coastline Tuesday. Precipitation chances throughout Central California will increase Tuesday night and Wednesday as this atmospheric disturbance moves southward down the coast of California. Nearly three-quarters of an inch of rain is possible in the San Joaqin Valley, north of Kern County, Tuesday night through Wednesday night. Rain amounts should remain below one half of an inch in the San Joaquin Valley portion of Kern County Tuesday night through Wednesday night. One to three feet of snow is conceivable in the Sierra Nevada above 7,000 feet Tuesday night through Wednesday night. A deep trough of low pressure will approach the coast of California Thursday. This robust trough of low pressure will move eastward through Central California Thursday night, before progress into the Great Basin Friday. Along with the possibility of additional precipitation, this trough of low pressure may also produce strong, gusty winds. Strong, gusty southerly winds are possible ahead of this trough of low pressure in the western portion of the San Joaquin Valley and Coastal Range Thursday afternoon into Thursday night. Strong, gusty westerly winds are conceivable in wake of this trough of low pressure in the Kern County desert Friday. && .AVIATION... MVFR ceilings in the San Joaquin Valley should dissipate at around 23z this afternoon. IFR conditions are possible in the San Joaquin Valley tonight into Sunday morning due to areas of fog. && .AIR QUALITY ISSUES... On Sunday December 19 2021... Fireplace/Wood Stove Burning Status is: No Burning Unless Registered in Fresno... Kern... Kings... Madera... Merced and Tulare Counties. Further information is available at Valleyair.org && .CERTAINTY... The level of certainty for days 1 and 2 is medium. The level of certainty for days 3 through 7 is medium. 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... None. && Update...Andersen Public/Aviation/Fire Weather...BS PIO/DSS...DCH weather.gov/hanford
The national radar mosaic for the moment the first event began.
5 dense fog. Local standard time, as filed.
Visibility below a quarter mile was reported in Atwater, Merced and Madera.
Visibility below a quarter mile was reported in Hanford.
Visibility below a quarter mile was reported in Bakersfield.
Visibility below a quarter mile was reported in Lemoore.
Visibility below a quarter mile was reported in Visalia.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, December 2021
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: 989769, 989771, 989774, 989773, 989772.