Torrential rain from an atmospheric river with locally heavy convective showers brought flash flooding to portions of the northern Sierra and Motherlode foothills. The heaviest flooding was in Groveland, where 4-5 of rain fell, combining with 8-9 of rain in higher elevations upstream.
Every event with a place to put it. 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 STO wrote it up.
Torrential rain from an atmospheric river with locally heavy convective showers brought flash flooding to portions of the northern Sierra and Motherlode foothills. The heaviest flooding was in Groveland, where 4-5 of rain fell, combining with 8-9 of rain in higher elevations upstream. There was also widespread damage in Tuolumne County to roads from debris flows, soil erosion, erosion of water conveyance systems, sewer systems that were inundated with excess water and debris. Roads damaged inluded state Highways 49 and 132. Moccasin Dam was damaged and came close to failure, with road closures. A tornado struck an amphitheater in Wheatland and caused minor damage. Heavy snow caused travel problems over Sierra highways.
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 Mar 21, 2:50 AM PST, 5 hours 10 minutes earlier.
Area Forecast Discussion National Weather Service Sacramento CA 350 AM PDT Wed Mar 21 2018 .SYNOPSIS... Wet weather continues into the weekend. Snow will remain above pass levels through most of tonight, then will lower with significant accumulations possible at the higher elevations. && .DISCUSSION... Initial wave moved through late Tuesday and earlier in the night with most of the region receiving between 1/4 and 3/4's of an inch of rain. Areas of mostly light to moderate precipitation continue in the warm air advection environment. Snow level radars at Chico and Colfax indicate the snow level remains above 8000 feet. Current temperatures are very mild ranging from the upper 30s and 40s in the mountains to the upper 40s to mid 50s across the Central Valley. Off and on light precipitation will continue across the valley today, though there will be conditional threat for some thunderstorms by mid-afternoon that will be accompanied by heavy rain and gusty winds. Forecast soundings indicate a lower-level cap which may be overcome with enough surface heating (if there are any breaks long enough to allow for it), but sufficient elevated CAPE (250-500 j/kg). Precipitation expected to increase across the region tonight into early Thursday as the surface front approaches and moisture transport from the south increases. Much of the valley expected to see around an inch of rain with 2-4 inches over the mountains where orographic enhancement will increase. Have decided to let the Winter Storm Watch continue for now as it's looking more likely that snow levels will remain high into Thursday. Winds will also increase across the area. Strong cold front will sweep southeast around midday with snow levels lowering rapidly in its wake during the afternoon. As mentioned above, confidence in the exact timing of frontal passage and lowering snow levels is not high at this time and some changes to details are likely. Travel is likely to deteriorate rapidly later in the day as this change over occurs. Stay tuned to the latest forecasts updates. Thunderstorms possible again Thursday in the dry slot behind the front. Brief heavy rain and small hail likely the primary concerns. Over the northern Sierra, a relatively quick shot of heavy snow will be possible into the evening before precipitation tapers. A brief break in the wet weather looks possible late Thursday night and Friday morning before a colder system brings potential heavier snow to the mountains Friday into Saturday. && .EXTENDED DISCUSSION (Sunday THROUGH Wednesday) Main upper trough shifts east of the state during the day on Sunday bringing the last of the precipitation for a while as upper ridging builds over the eastern Pacific. Precipitation chances will mainly be restricted to east of the central valley. Precipitation amounts will be quite light but snow levels will be abnormally low at around 1500 to 2500 feet. A few lingering showers may still be possible Sunday night but building high pressure will bring an end to any precipitation threat by Monday. Temperatures warm by several degrees on Monday but are still forecast to run slightly below normal. Upper level and surface gradients indicate breezy north winds which will help to start drying things out. Temperatures continue to warm on Tuesday as upper ridge pushes inland with highs expected to warm to several degrees above normal. Even more warming is expected on Wednesday with highs throughout the valley expected to reach the mid 70s in the northern Sacramento valley. Breezy north winds will continue through the period between an upper low over the southwest U.S and building high pressure over the eastern Pacific. && .AVIATION... Mainly MVFR/IFR conditions next 24 hours TAF sites as Pacific storm system pushes through the region. Mainly IFR over mountains. Snow levels 6500 to 7500 feet. Southerly wind increasing after 00z Thursday with gusts to 25 knots northern Sacramento valley to 45 knots over the higher Sierra. && .STO WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from this evening through Thursday evening for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. &&
The Beale AFB radar (KBBX), 69 km away, was scanning. The volume nearest the first event began at 16:02 UTC.
7 flood, 2 funnel cloud, 1 heavy snow, 1 dense fog, 1 tornado, 1 flash flood. Local standard time, as filed.
Combie road flooded due to overtopping of the adjacent Ragsdale Creek.
Closed lanes on Highway 50 at Latrobe Rd/El Dorado Hills due to rockslide.
Street flooding on Dean Way east of Wales Dr. in Folsom.
Street flooding in Cameron Park Estates Mobile Home Park. Video via Twitter.
Heavy snow fell, causing travel slowdowns disruptions over higher elevations of mountain highways including I80 and Highway 50. At Kirkwood Ski Resort, a storm total of 32 of new snow was reported, 31 at North Star, 24 at Sierra at Tahoe. There was 8 of new snow at Kingvale, elevation 6100'.
Vehicle stuck in a flooded roadway on Scott Rd. and Latrobe Rd.
Extensive flooding in downtown Groveland, as floodwaters ran down the main street, Highway 120. Property was damage and water rescues for stranded residents. There was significant damage done to Groveland Community Hall and Mary Laveroni Community Park. Preliminary estimates from Tuolumne County are approximately $8 million for 16 damaged sites along county maintained roads. A very large portion of these damages are seen in the sinkhole at Ferretti Road and slides and embankment loss on Priest Coulterville Road.
There were 5 vehicles involved in an accident attributed to dense fog. There were 7 injuries reported.
A funnel cloud was observed, weakening. Dime size hail was also observed.
A funnel cloud was observed, extending halfway to the ground.
Tornado touchdown observed by Yuba County deputies at Yuba County. Minor damage was observed, including ripped tarps and objects knocked over. Another touchdown was observed and videoed in an open field, about a mile to the north. No damage was observed at the second touchdown location.
A period of heavy rain upstream from Moccasin Dam, in which about three inches fell during four hours led to significant erosion and at least one landslide. It caused a massive amount of water and debris to run downhill into the Moccasin Reservoir. The water level rose to 3 times the normal reservoir capacity and the emergency spillway was utilized. There was severe erosion of the emergency spillway and potential for the dam to fail. The Power house and staff at the Moccasin Fish Hatchery were evacuated due to potential failure. All the fish in the Moccasin Creek Hatchery were killed when it flooded from the water coming over the emergency spillway. The National Weather Service issued a flash flood warning associated with the probable dam failure, and the sheriff advised residents to avoid the area as a matter of public safety. The warning was reduced to a watch until the reservoir was drained and then the watch was canceled once the reservoir was drained.
Cleanup and repair efforts associated with a major storm that damaged Tuolumne County's Moccasin Creek Dam in March is expected to cost roughly $43 million, according to an estimate by the San Francisco Public Utilities Commission, which owns and operates the dam. That total includes $3.2 million in damage to the state fish hatchery at Moccasin Creek, which lies downstream.
Heavy rain caused a railroad bridge in Marysville to sink. The bridge spans the Yuba River. Rail traffic over the bridge was shut down. A diesel pipeline attached to the bridge also had to be shut down. Union Pacific Railroad drove in new piles to stabilize the bridge. Repairs were completed on March 27.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyThe tornado archive for California, 2018Warnings in California, March 2018
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: 747036, 747037, 747038, 747039, 747047, 747040, 747042, 747048, 747043, 747044, 747045, 747046, 747175.