A strong atmospheric river event produced a major heavy rain, high wind, and high elevation snow event for much of the region. Record-setting rainfall amounts for many areas of the Sierra into western Nevada.
Every event with a place to put it; 5 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 REV wrote it up.
A strong atmospheric river event produced a major heavy rain, high wind, and high elevation snow event for much of the region. Record-setting rainfall amounts for many areas of the Sierra into western Nevada. NWS Reno received multiple reports of mud and rock slides in the Sierra along I-80 near the summit, and CA 70 and CA 89 in Sierra, Plumas, and Lassen Counties.
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 Reno, NV wrote its last area forecast discussion before the first event at Oct 22, 2:02 AM PST, 7 hours 58 minutes earlier.
Area Forecast Discussion
National Weather Service Reno NV
302 AM PDT Fri Oct 22 2021
.SYNOPSIS...
Plan on periods of rain, high elevation snow, and gusty winds as the
active weather pattern continues through the weekend. An initial
system moves through this morning then as stronger and much wetter
system is forecast for Sunday through Tuesday with potential
impacts from strong winds, soaking rains, and heavy mountain snow.
&&
.SHORT TERM...Today through Monday morning
We are going to be unusually wet through early next week,
potentially setting precipitation records for October in some
locations if things continue to look the way they are looking. Now
is the time to prepare and make sure your drainage areas and gutters
are cleaned out!
Moist flow continues with upslope ascent keeping light showers going
on and off into the Sierra and instability allowing for some
spillover into western Nevada. We can already see the next system
with a Pacific moisture feed moving into northern CA on satellite
and radar. This is the first atmospheric river (AR) in the series
that will affect the region through today.
*First system – Continues through Friday:
Decent push of moisture into the Sierra, primarily near and north of
Ebbetts Pass, with relatively high snow levels (8500-10000 feet).
Deep southerly flow will keep the best precipitation on western
slopes, with not much spillover until late morning into midday
Friday as the upper trough shifts inland. A Flash Flood and Debris
Flow Watch remains in effect for the Dixie, Sheep, Walker, and
Beckwourth burn scars.
Current radar shows a band of showers currently moving across the
northern half of CA but no NCFR signatures present at this time.
Hi-RES CAM guidance did show a narrow band of showers and heavier
embedded precipitation moving into the northern Sierra earlier
this morning hours but little chance this will continue through
the remainder of the morning hours. Snow levels do fall behind the
cold front on Friday, reaching around 6500-7500 feet by late
Friday afternoon, however, the bulk of the more persistent
precipitation will have already moved on into the Great Basin.
Lingering showers could contribute to pass level travel
difficulties from late afternoon into the early evening hours.
Winds will remain breezy through Friday with the cold front
continuing east into the Great Basin region. Valleys may see still
gusts 25-35 mph with ridges potentially exceeding 80 mph.
Remnant moist flow will keep periods of showers going Saturday, but
this looks to be mainly confined to the northern Sierra and far
northern NV.
*The main event - Sunday through Monday morning:
Significant atmospheric river still on track late weekend into early
next week with heavy rain and mountain snow looking almost certain.
The lower end of the qpf scenarios in the ensemble guidance
continues to trend upward with the EC EFI indicating this is a very
anomalous event. Looking at the QPF forecasts compared to the 20-
year reforecast period, this is indicating liquid totals higher than
any event in the past 20 years for these locations at this lead
time. While there is still variation in the lee-side liquid totals,
even the low end guidance is rather impressive for spillover. This
coupled with an ideal synoptic setup and a massive moisture tap is
giving us higher confidence for a major precipitation event
throughout the entire region.
Snow levels will start rather high, around 8,500-10,000 feet, but
will fall during the day Monday. The question at this point is how
fast will they fall. Current forecast would hint at pass level
impacts by Monday morning, with snow levels crashing to around 5500-
6000 feet by Monday night. The upper elevations of the Sierra could
see feet of heavy wet snow, but many communities in the Tahoe Basin
and those along US-395 in the Eastern Sierra are likely to only see
a few inches of snow at most. Just keep in mind -- we could see
dramatically different snow amounts at various elevations. Winter
Storm Watches have been issued for the high Sierra, please see the
products for additional details.
Despite the copious amounts of rain, the dry soils and large amount
of available storage in reservoirs will mitigate widespread flood
risks, especially for mainstem rivers, however, they will see rises.
Smaller creeks and streams tend to be more flashy and could be more
of a concern, and urban/poor drainage flooding is certainly possible
as well. The greatest threat will be the recent burn scars -- really
any major burns in the past couple of years in the Sierra and/or
western Nevada foothills. This will be the first real test for
several burns, including but not limited to: Caldor East, Tamarack,
Slink, and Numbers. Dixie East, Beckwourth, Sheep, and Walker will
have already been tested with the first AR, but will be pushed
again with this stronger AR. The greatest flood threat will be
during the warmer part of the storm Sunday into early Monday.
Mudslides and debris flows or rockslides are all on the table for
possibilities, so travel could get dicey in the Sierra.
Winds aloft will be rather strong Sunday night into Monday morning,
but given the intense precipitation rates, we are not likely to see
as strong wind speeds at the surface. Valley gusts could still
exceed 40 mph at times, with 100 mph across the ridgelines. These
winds will bring periods of travel and recreation concerns along
with bumpy flights for aviators. The other concern will be areas
where trees are weakened by wildfires and are susceptible to
falling. -Dawn/Amanda
.LONG TERM...Monday through Friday.
By Monday morning, the core of the very strong polar jet stream
is forecast to move south of I-80 which will begin to allow colder
air into the region. Snow levels around 7000' along Donner Summit
will drop rapidly through the day down to around 5000' by Monday
night. However, as the snow levels rapidly fall on Monday, so will
the precipitation intensity, as the atmospheric river moves south
of the region. Current expectations are for 2+ feet along the
higher road passes with 8-12" along donner summit, but only a few
inches around Lake Tahoe and along highway 395 in Mono County. As
is usually the case here in the Sierra, there does remain
uncertainty in the timing of snow levels dropping and when the
precipitation begins to taper off, so if your plans involve travel
in the Sierra Sunday through Monday night check back for forecast
updates and prepare for snowy travel.
Temperatures will be quite cool on Monday and Tuesday with only
moderate warming through the week. After Tuesday night, a break in
precipitation looks likely for the rest of the week as a broad
area of high pressure builds over the region pushing the jetstream
back into the Pacific Northwest. -Zach
&&
.AVIATION...
Scattered showers may bring lower CIGS/VIS and MVFR conditions
through the late morning hours especially for Sierra terminals KTRK-
KTVL where heavier precipitation is expected at those terminals.
Southerly winds ahead of an incoming cold front will gust 20-25kts
this morning for most terminals with winds shifting from the west
after passage of the front early afternoon. KMMH will be gusting 30-
35kts ahead of and following frontal passage this afternoon.
The increased winds will bring the possibility of another round of
LLWS in areas around KRNO through this afternoon.
A much stronger and wetter Pacific system will impact the region
Sunday morning into Monday with strong winds and heavy rain for
terminals across the region. VIS/CIG could lower terminal conditions
across Sierra and western NV terminals down to IFR/LIFR in heavier
precipitation. There are chances for accumulating snow at
KTRK/KTVL/KMMH Monday. -Amanda
&&
.REV Watches/Warnings/Advisories...
NV... Flood Watch from late Saturday night through Monday morning
NVZ002-003.
Winter Storm Watch from Sunday evening through Monday evening
above 8000 feet in NVZ002.
CA...Flood Watch from Saturday evening through late Sunday night
CAZ071.
Flash Flood Watch until 11 AM PDT this morning CAZ071.
Flood Watch from Sunday morning through Monday afternoon CAZ073.
Winter Storm Watch from Sunday afternoon through Monday evening
above 9000 feet in CAZ073.
Flood Watch from late Saturday night through Monday morning
CAZ072.
Winter Storm Watch from Sunday evening through Monday evening
above 8000 feet in CAZ072.
&&
For more information from the National Weather Service visit...
http://weather.gov/renoThe Reno radar (KRGX), 193 km away, was scanning. The volume nearest the first event began at 17:59 UTC.
9 heavy rain, 7 debris flow, 4 heavy snow, 2 flash flood, 1 high wind. Local standard time, as filed.
COOP and CoCoRahs observers, as well as Mesonet/ASOS sites, reported rainfall amounts ranging from 1.0-3.0 around Walker, CA, to the Lee Vining/Mono Lake area with 4.0-6.0 around the Crestview to Mammouth Lakes, CA region.
CoCoRahs Observers, trained spotters, and Mesonet/ASOS sites reported rainfall amounts ranging from 0.5-3.0 in the area between Janesville to Susanville, CA; 3.0-4.0 in the Westwood to Lake Almanor region; and up to 6.0 about 3.0 mi SSW of Susanville, CA.
Trained spotter in Doyle at an elevation of 4500 feet reported 7.28 inches of rain as of midnight (24 hour period starting 24/0001 LST) with an additional 1.49 inches falling since midnight. The spotter also reported that snow was falling around midnight but not accumulating. Total rainfall amount of 8.77 was reported at this site.
COOPs observers and Mesonet/ASOS sites reported rainfall amounts ranging from 0.3-1.0 in the far NE corner of Modoc county in and around Fort Bidwell, CA, as well as 1.0 -2.0 within the area from Cedarville, CA to Lake City, CA.
CoCoRahs Observers, trained spotter, and Mesonet/ASOS sites reported rainfall amounts 1.0-2.0 around Echo Lake, 2.0-4.0 from Echo Summit to Meyers, CA; and 6.0-8.0 reported from Meyers, CA to South Lake Tahoe, CA.
A trained spotter located 2.0mi NW of Meyers, CA (COCORAHS STATION CA-ED-20) reported 24 hour total for rain-snow melt of 8.40 inches. The trained spotter also reported 4 inches of snow fell with SWE of 1.14 inches.
A trained spotter in Placer County, 1.0 mi NNW of Homewood, CA measured 12 inches of snow along with 6.4 inches of liquid over the previous 24 hours.
Public reported 18 inches of snow at Lake Davis in Plumas, County.
Law Enforcement in Nevada County reported 25 inches of snow near soda springs or 7 mi W of Truckee, CA, since 10 PM on 23OCT.
Law enforcement reported several areas with debris in the roadway, and the culvert under the railway is plugged.
California Highway Patrol reported large rocks in roadway on Gold Lake road above Graeagle Lodge.
California Highway Patrol reported rocks, mud in road near Chilicoot Campground.
California Highway Patrol reported a large (larger than a basketball) boulder in the road on State Highway 70 near Camp Layman Road.
US Highway 50 is closed due to a late night rock fall near Echo Summit.
California Highway Patrol reported the left lane on us 395 at Conway Ranch Road is closed due to a large rock in the roadway.
California Highway Patrol reported a large boulder in the middle of the westbound lane of US Highway 89.
California Highway Patrol reported 3.5 feet of water over the road on the north end of Constantia Road making the roadway impassable.
California Highway Patrol reported ton of rocks and water come off the mountain side of old 40, (Donner Pass Rd between Truckee and Donner Summit.) the road is now closed as it is not safe to pass due to erosion and falling debris.
Broadcast Media and PG&E reported several inches of heavy wet snow around the South Lake Tahoe area. Echo Summit received up to a foot of new snow. PG&E reported about 5 inches of snow which resulted in a power outage in the South Lake Tahoe area.
COOP and CoCoRahs observers, trained spotters, and Mesonet/ASOS sites reported rainfall amounts ranging from 1.0-3.0 in the area of Glenshire-Devonshire/Donner Peak, CA, and 4.0-6.0 in and around Truckee, CA.
Several CoCoRahs Observers and Mesonet/ASOS sites reported rainfall amounts ranging from 0.4-1.0 near Independence Lake, 2.0-4.0 in and around Portola, CA, and 4.0-6.0 west of Verdi, NV.
Several Mesonet/ASOS sites reported rainfall amounts ranging around 1.0 near Cromberg, CA; 2.0-4.0 west of Janesville, CA; and 4.0-6.0 SE of Frenchman Lake.
CoCoRahs Observers, trained spotters, and Mesonet/ASOS sites reported rainfall amounts ranging from 1.0-2.0 near Alpine Meadows ski resort, 2.0-5.0 in and around Homewood, CA, and as much as 6.0 at Tahoe City, CA.
About 4.38 of rainfall reported by mesonet station MKEC1 located 0.88mi SW of Markleeville, CA.
A peak wind gust of 159 mph was recorded from the summit of Mammoth Mountain at an elevation of 11,053 feet.
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, October 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: 987732, 987742, 987736, 987744, 987338, 987339, 987337, 987314, 987323, 987324, 987330, 987331, 987332, 987333, 987334, 987335, 987336, 987721, 987603, 987604, 987716, 987743, 987340.