A wet system brought periods of moderate to heavy rain with scattered thunderstorms. Lines of stronger thunderstorms brought local road flooding to portions of interior Northern California.
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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 STO wrote it up.
A wet system brought periods of moderate to heavy rain with scattered thunderstorms. Lines of stronger thunderstorms brought local road flooding to portions of interior Northern California. There was also a confirmed EF-1 tornado touchdown in the Oroville area, with minor damage. Snow levels were high, with impacts limited to minor travel delays for Sierra pass levels.
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 Sacramento, CA wrote its last area forecast discussion before the first event at Dec 18, 1:38 AM PST, 4 hours 52 minutes earlier.
Area Forecast Discussion National Weather Service Sacramento CA 138 AM PST Mon Dec 18 2023 .Synopsis... Periods of moderate to heavy rain, high elevation snow, and isolated thunderstorm chances continue today through Wednesday. Gusty southerly winds are also expected Monday into Tuesday. Quieter and seasonable weather is then anticipated late week into next weekend. && .Discussion... Early this morning, mostly cloudy skies are evident across interior NorCal via latest GOES-West imagery. Scattered rain showers and a few embedded thunderstorms are also present along and west of the I- 5 corridor at this time. This activity looks to gradually spread east-northeastward through the overnight, becoming more widespread by the morning. Resultant overnight low temperatures will remain comparatively mild, with Valley lows in the mid to upper 40s and upper 20s to low 30s in the mountains. Precipitation chances will continue across the early week period and through Wednesday before tapering off throughout the day on Thursday. Latest probabilities of exceeding 1" of QPF during this time frame remain high, in the 90 to 100% range across the region, with probabilities of exceeding 3" in the 30 to 60% range in the Valley and 70 to 90% range over the mountains. Despite this being a a relatively warm system, high elevation accumulating snow is still expected. Snow levels generally remain in the 7500 to 8000 foot range for much of the event until they drop to the 6500 to 7500 foot range late Tuesday into Wednesday. This will likely keep the bulk of the accumulating snowfall to high elevation mountain peak levels. Latest probabilities of exceeding 4" of snowfall for elevations greater than 7000 feet are in the 50 to 90% range, with probabilities of exceeding 8" in the 40 to 80% range. Best chances for heaviest snowfall are expected near Lassen Peak and for areas south of the Highway 50 corridor. Furthermore, a 15 to 25% chance for isolated thunderstorms will remain possible through Tuesday. This is the result of increasing moisture to the region, amidst a fairly mild temperatures regime, leading to some weak instability. Best chances for thunderstorm development will be across portions of the Delta, Valley, and adjacent foothills locations. With any thunderstorms that do develop, gusty winds, brief heavy rainfall, and small hail will be the primary hazards. Gusty southerly winds will also increase later today into Tuesday morning as the trough begins to move further inland. Sustained winds of 15 to 25 mph are anticipated with occasional gusts 30 to 45 mph. Strongest winds are expected over the northern Sacramento Valley and across the Sierra. Resultant probabilities of wind gusts exceeding 40 mph for these areas are in the 40 to 70% range. && .EXTENDED DISCUSSION (Friday THROUGH Monday)... Late week into next weekend is expected to see much quieter weather across much of the region as troughing over southern California dominates the weather pattern. A weak shortwave embedded in this pattern may bring some isolated showers to portions of the forecast area early in the weekend, but rainfall totals look to remain light and generally confined to the mountains. Otherwise, seasonable temperatures prevail through the long term period. && .AVIATION... Mainly VFR conditions persist early this morning (except for areas of MVFR visibilities across the northern San Joaquin Valley) with scattered showers and a few thunderstorms. MVFR, with local IFR, conditions become predominate after 18Z as more numerous showers and isolated thunderstorms move over NorCal. Areas of southerly surface wind gusts 15-25 kts develop after 20Z, then widespread southerly gusts 25-35 kts increase by 06Z Tuesday. && .STO WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 10 PM this evening to 7 AM PST Tuesday for Central Sacramento Valley-Northeast Foothills/Sacramento Valley- Northern Sacramento Valley. &&
The Sacramento radar (KDAX), 43 km away, was scanning. The volume nearest the first event began at 14:31 UTC.
7 flood, 1 heavy rain, 1 tornado. Local standard time, as filed.
CHP reported roadway flooding on I-80 Eastbound/Travis Blvd off-ramp.
CHP reported standing water on I-80 West at the Waterman Blvd. off-ramp.
CHP reported that the #1 lane at southbound I5 - US 50 E connection/P St on-amp had 2-3 inches of water collected on the roadway.
CHP reported roadway flooding at Lower Sacramento Rd. and E Woodson Rd.
CHP reported /responded to HAZMAT incident caused by a truck hydroplaning on I-5N near Lamoine Rd due to moderate to heavy rain. The incident was mostly cleared at 1:30 PM PST. There was 1.25 of rain reported.
CHP reported roadway flooding at the intersection of Fulkerth Rd and Faith Home Rd.
CHP/Cal Trans reported a rock slide on the road near Potato Patch Campground. Rocks were in both lanes and are being cleared by Cal Trans.
National Weather Service Meteorologists surveyed storm damage in Oroville, and analyzed radar and video evidence. It was determined that an EF-1 tornado, associated with a line of thunderstorms, moved through for about 2 minutes before lifting, resulting in tree and minor structure damage.
CHP reported Mud/Dirt/Rock starting to come downhill and cross the roadway, US50/Bridal Veil Falls, eastbound.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2023Every state in 2023This day in weather historyThe tornado archive for California, 2023Warnings in California, December 2023
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: 1153732, 1153733, 1153734, 1153735, 1153737, 1153736, 1153748, 1153731, 1153746.