A deep upper trough with a warm subtropical moisture fetch in front of it pushed into central California during the evening of December 22 and brought a period of rain and higher elevation snow to the area which continued through the evening of December 23. Several stations in the Sierra Nevada measured between 1 and 3 inches of liquid precipitation with the snow level between 8000 and 9000 feet.
Every event with a place to put it; 3 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.
A deep upper trough with a warm subtropical moisture fetch in front of it pushed into central California during the evening of December 22 and brought a period of rain and higher elevation snow to the area which continued through the evening of December 23. Several stations in the Sierra Nevada measured between 1 and 3 inches of liquid precipitation with the snow level between 8000 and 9000 feet. Rain shadowing kept precipitation amounts in the San Joaquin Valley lower with a half inch to an inch of rain on the east side and a quarter to half inch of the west side. Some localized nuisance flooding was reported during the afternoon of December 23. Cooler air pushed into the area during the evening of December 23 resulting in showery precipitation which continued through the early morning of December 24. A few higher elevation SNOTELs picked up an estimated 18 to 24 inches of new snowfall. Some ice pellet showers and a few thunderstorms were observed in the Sierra foothills and the snow level in the Sierra Nevada lowered to around 5500 feet before the precipitation tapered off.
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 22, 4:01 PM PST, 11 hours 59 minutes earlier.
Area Forecast Discussion...UPDATED National Weather Service Hanford CA 401 PM PST Wed Dec 22 2021 .UPDATE...Updated Air Quality Section. && .SYNOPSIS...A very wet weather pattern will continue through the next few days as several weather disturbances move into and across the Central California Interior. Heavy mountain snow and significant lower elevation rain will occur through the middle of next week. && .DISCUSSION...Area radars show increasing coverage and intensity of incoming precipitation as it moves onshore in the southwest flow. Satellite imagery shows a very active baroclinic zone stretching to the southwest out several hundred miles and water vapor imagery shows the southern branch of the jet stream enhancing the clouds. High resolution rapid refresh modeling targets areas generally south of Yosemite through the evening hours with the most concentrated precipitation and then in the early morning hours brings another band of moderate to heavy precipitation into northern parts of the area. So...between the two disturbances, everyone will get at least some precipitation. Snow levels will start out rather high with the first impulse due to the lower latitude origin of the airmass associated with the front. Area snow level radar data suggests the snow level starting out around 9000 feet this afternoon and model data suggests that the snow levels will stay in the 8000-9000 foot range through the next 24 hours or so as the warm, subtropical atmospheric river targets the forecast area. Models then keep the atmospheric river targeting the Central California Interior into Friday before it shifts to the southeast and the precipitation takes a Christmas Eve break. Total snowfall amounts in the Sierra above 7500 feet could reach to as much as 120+ inches over the higher terrain as the topography lines up perpendicular to the moist atmospheric river flow. Meanwhile, below the snow line precipitation amounts in the Sierra and foothills will likely range in the 3-6 inch range through early Saturday. Lower elevations such as the San Joaquin Valley will most likely receive 1-2 inches of rain, especially on the east side of the valley where the orographic lift of the Sierra just to the east will begin to play a role in enhancing the rainfall. Over the Kern County Desert areas, enough moisture be available in the southwest flow to give generally 0.35 to 0.75 inches of rain through Friday night. Latest deterministic models give the area about a 24 hour break from rain and snow for much of Christmas Day, however the next impulse drops in from the northwest by Saturday evening. This feature will have colder air and snow levels will begin to drop to as low as 2500-3500 feet on Sunday. This will bring the potential for serious travel problems on one of the most busy travel days of the year. Another rather cold weather disturbance follows behind the Sunday feature on Monday with yet more rain and lower elevation snow. Forecast models then diverge on how the pattern will evolve into the middle of next week with the ECMWF model driving a very cold trough of low pressure into California on Wednesday while the latest deterministic run of the GFS forms an offshore cold, closed low. Ensemble National Blend of Model probability of precipitation exceeding 0.01 inches shows a 62 percent chance at Merced and 30 percent chance in the Edwards AFB region. So...all in all a very active weather pattern with abundant rain and snow, the potential for travel problems and even some very low elevation snow next week. Winter storm warning will remain in effect for the Sierra for higher elevation very heavy snow through Friday. Will need to also watch burn scars for lower elevation heavy rains that may cause debris flows, especially if the rainfall rates become excessive. && .AVIATION...MVFR conditions are likely in and near showers over the next 24 hours. Local IFR conditions are expected in the Sierra Nevada through at least the next 24 hours. && .AIR QUALITY ISSUES...On Thursday December 23 2021... Fireplace/Wood Stove Burning Status is: No Burning Unless Registered in Fresno... Kern... Kern (Greater Frazier Park Area) and Madera Counties. Further information is available at Valleyair.org && .CERTAINTY... The level of certainty for days 1 and 2 is high. 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 Warning until 4 PM PST Sunday for CAZ323-326>331. && public...Dudley aviation....Dudley weather.gov/hanford
The national radar mosaic for the moment the first event began.
4 flood, 3 heavy snow, 1 debris flow. Local standard time, as filed.
The Tuolumne Meadows SNOTEL (8600 ft) picked up an estimated 18 inches of new snowfall.
The Upper Tyndall Creek SNOTEL (11443 ft) picked up an estimated 22 inches of new snowfall.
The Bishop Pass SNOTEL (11972 ft) picked up an estimated 23 inches of new snowfall.
California Highway Patrol reported roadway flooding at the intersection of E. Copper Ave. and Auberry Rd.
California Highway Patrol reported roadway flooding at the itnersection of N. Madera Ave. and W. Shaw Ave.
California Highway Patrol reported roadway flooding at the intersection of SR 168 and Sparrow Rd.
California Highway Patrol reported roadway flooding at the intersection of SR 65 and Harvard Ave.
California Highway Patrol reported a large boulder on the road at the intersection of Crest Ln. and Sierra King Dr.
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: 990431, 990432, 990433, 990426, 990427, 990428, 990429, 990430.