A winter storm brought bountiful Valley rain and mountain snow to interior northern California. 75 inches of rain.
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 winter storm brought bountiful Valley rain and mountain snow to interior northern California. Valley and foothill rain amounts generally ranged from 0.5 to 1.75 inches of rain. Snow levels for this storm were around 3500 feet for Shasta County and the southern Cascades, while the Sierra observed snow levels closer to 4500 feet. This allowed for hazardous driving conditions in the mountains as periods of moderate to heavy snow would result in chain controls, reduced visibility, and slick roads. No snow reports have been found for zones 13 and 69.
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 13, 3:39 AM PST, 3 hours 21 minutes earlier.
Area Forecast Discussion National Weather Service Sacramento CA 339 AM PST Sun Dec 13 2020 .SYNOPSIS... A winter storm will bring rain and mountain snow today, causing travel difficulties. Dry early next week before unsettled weather returns mid to late week. && .DISCUSSION... The forecasted weather system remains on track as the upper level trough is beginning to make its way inland early this morning. Radar imagery has been showing bands of precipitation moving in from the west for areas north of Interstate 80. As the surface cold front moves through the area this morning, precipitation will become more widespread. Periods of moderate rainfall and moderate to heavy mountain snowfall are expected with the frontal passage this morning through early afternoon. The heaviest snowfall is expected over the western slopes of the Sierra with around 10 to 20 feet above 4500 to 5500 feet, most of which is expected to fall by mid afternoon. The Shasta County mountains will see up to 8 to 12 inches for elevations above 3500 to 4500 feet. A Winter Storm Warning remains in effect for the Sierra and a Winter Weather Advisory for the Shasta County mountains. This snowfall could create significant travel delays, especially over the Sierra passes as hourly snow rates could reach an inch per hour from mid morning through mid afternoon. After the surface front passes through the area this morning, short term models continue to indicate some post-frontal instability this afternoon. Areas north of Interstate 80 could see some stronger scattered showers this afternoon with a slight chance of thunderstorms. The bulk of the precipitation will move through by the early evening hours, with mountain showers lingering through the night. HREF is indicating a high potential for fog across the area tonight into tomorrow morning. Dense fog is possible at times for Valley, foothill, and mountain locations. Dry weather returns Monday into Tuesday for most of the area as upper level ridging takes over. Models continue to indicate a weak shortwave could brush northwestern California on Tuesday, bringing a slight chance of showers to the higher elevations in Shasta County. Another Pacific trough is expected to bring the next weather system to the area midweek. At this time, models suggest the trough will begin moving inland Wednesday, with heavier precipitation beginning Wednesday night into Thursday. -HEC && .EXTENDED DISCUSSION (Thursday THROUGH Sunday)... Confidence is increasing in the mid-week storm system with the Days 4 and 5 5H Clusters suggesting a digging trof over Norcal and into the Great Basin Thu/Fri. With confidence increasing we increased PoPs/QPFs accordingly, blending to the WPC guidance available at the time. The GFS Prob of IVT tool indicates there is plume of moisture then, with the GEFS IVT Plume Forecast indicating the potential for a weak AR, along 38-39N, arguably a little wetter than what we looked at yesterday. Currently looks like the west slopes of the Sierra Nevada could receive between one and two inches of precipitation and a tenth to two-thirds of an inch in the Valley. Dry weather returns Fri/Sat with the next system arriving on Sun/Mon. A strong westerly Pacific jet stream is forecast to slam into the Pac NW bringing with it a "Winter Solstice" Storm (Solstice occurs on 12/21 at 2:02 am PST this year). Although the GFS is deeper with the low center, the ECMWF is more progressive/faster driving the trof through our CWA by Tue, while the GFS lags behind. JHM && .AVIATION... Widespread IFR/MVFR conditions in precip as surface front moves across Norcal this morning and lingers over the Sierra most of the evening. SE winds at 30-37 kts at 2 thousand ft may result in LLWS (speed shear) at valley terminals thru 18-20z ahead of frontal boundary. During afternoon, colder, unstable air forecast to move inland over Nrn Sac Vly with the potential for isolated to scattered TSRA. Even though rain will end by/during the early evening in the Valley, a moist air mass will result in persistent stratus and fog with lingering IFR/MVFR conditions overnite. && .STO WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 7 AM this morning to 4 AM PST Monday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. Winter Weather Advisory until 10 PM PST this evening for Burney Basin / Eastern Shasta County-Shasta Lake Area / Northern Shasta County. &&
2 winter storm. Local standard time, as filed.
Storm total snow accumulation reports from the ski resorts peppered across the Sierra varied between 9 to 17 inches of snow.
Caltrans reported 7 inches of snow at their Kingvale maintenance yard, 9 inches of snow at Donner Summit, and 13 inches of snow at Soda Springs.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2020Every state in 2020This day in weather historyWarnings in California, December 2020
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: 934817, 934818.