High pressure shifted east across California on December 19 and 20. As a result with areas of dense fog reformed in the San Joaquin Valley during the evening of December 19 as clear skies, light winds and inversion conditions prevailed.
Every event with a place to put it; 4 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 shifted east across California on December 19 and 20. As a result with areas of dense fog reformed in the San Joaquin Valley during the evening of December 19 as clear skies, light winds and inversion conditions prevailed. The fog lifted into a low cloud deck in most of the valley overnight, but persisted well into the morning in the south end of the valley before lifting into a low cloud deck.
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 19, 4:37 PM PST, 2 hours 58 minutes earlier.
Area Forecast Discussion National Weather Service Hanford CA 437 PM PST Sun Dec 19 2021 .UPDATE...Updated for the air quality section. && .SYNOPSIS... A cold air mass over Central California will bring near freezing temperatures to rural areas of the San Joaquin Valley again tonight. Fog is likely to develop again and may become widespread and dense overnight. Precipitation chances will increase Tuesday night and Wednesday as a strong storm system approaches the coast. Moderate to heavy rain and mountain snow will be possible later next week. && .DISCUSSION... It was a cold and foggy morning across much of the San Joaquin Valley today. Dense fog lingered until Noon with both Merced and Lemoore just now climbing to 1 mile visibility this afternoon. Visible satellite loops show much of the fog/low clouds clearing out across the SJV south of Fresno County. The fog/stratus shield remains fairly thick across Merced County down across western Fresno County. Expect fog to reform tonight but when, where, and how dense is a bit of a guess. Latest High Resolution Rapid Refresh guidance suggests it could be fairly widespread by midnight. Will hold off on an Advisory for now and let the evening shift monitor the situation and issue accordingly. Overnight temperatures will be similar to last night with freezing conditions in mainly rural areas of the SJ Valley and sub-freezing temperatures in the Desert. Monday will be dry and cool with light winds. A significant pattern change will occur this week as a strong storm system off the coast brings an extended period of wet weather. Precip chances begin on Tuesday but ensemble guidance has been trending a little slower and it's looking more likely to hold off until Tuesday night. A series of shortwaves are progged to impact the west coast through the end of the week bringing several rounds of precipitation. Latest QPF from Tues-Saturday has 1-2" of rain across the SJ Valley with rain shadowing limiting amounts along the west side and southern end of the valley. The Sierra and adjacent foothills are looking at 3 to 8 inches of rainfall possible. Snow levels will start out rather high at around 7000 feet through Wednesday, but will lower to around 5000 feet on Thursday and possibly 3000 feet on Friday. A Winter Storm Watch has been launched for the Sierra Nevada from Yosemite NP to Lake Isabella from late Tuesday night until Sunday afternoon. Rainfall in the Kern Mountains looks to range from 1 to 3 inches with around 0.5" in the Desert. Winds will increase Thursday night through Friday with breezy to windy conditions expected, especially across the Kern County Mountains. So lots of weather concerns with hazardous travel conditions looking likely for the coming week. && .AVIATION... Areas of MVFR and local IFR conditions in mist/fog across the San Joaquin Valley through 06z Monday. Becoming areas of IFR and local LIFR in fog after 06z through 19z Monday. Otherwise, VFR conditions will prevail across the central CA interior for the next 24 hours. && .AIR QUALITY ISSUES... On Monday December 20 2021... Unhealthy for sensitive groups in Fresno and Kern Counties. Fireplace/Wood Stove Burning Status is: No Burning Unless Registered in Kings... Madera... Merced and Tulare Counties. No Burning For All in Fresno and Kern 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... Winter Storm Watch from late Tuesday night through Sunday afternoon for CAZ323-326>331. && Public/Aviation/Fire Weather...DCH PIO/DSS........................JEB weather.gov/hanford
The national radar mosaic for the moment the first event began.
4 dense fog. Local standard time, as filed.
Visibility below a quarter mile was reported in Porterville.
Visibility below a quarter mile was reported in Atwater and Merced.
Visibility below a quarter mile was reported in Bakersfield.
Visibility below a quarter mile was reported in Fresno.
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: 989777, 989775, 989778, 989776.