A low pressure system brought wind, snow, heavy rain, and some debris flows to Southern California from November 29th through 30th. Strong wind associated with the frontal boundary made its way through Southern California on the 29th, with heavy rain behind it.
Every event with a place to put it; 4 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 SGX wrote it up.
A low pressure system brought wind, snow, heavy rain, and some debris flows to Southern California from November 29th through 30th. Strong wind associated with the frontal boundary made its way through Southern California on the 29th, with heavy rain behind it. These rains resulted in numerous flash floods and debris flows, closing roadways and impacting traffic. A few inches of snow fell in the San Bernardino Mountains on November 30th. Fawnskin reported 3 inches, Green Valley Lake reported 4 inches, and Big Bear Resort reported 4-8 inches.
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 San Diego, CA wrote its last area forecast discussion before the first event at Nov 28, 9:30 PM PST, 2 hours 30 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
930 PM PST Wed Nov 28 2018
.SYNOPSIS...
After a few showers tonight, A Pacific storm system will bring
widespread rain Thursday and Thursday night, with locally heavy
rain. A few thunderstorms are also possible. Some snow will occur in
the mountains late Thursday and Thursday night, mainly above 6000
feet. Strong gusty winds will occur, especially in the mountains and
deserts, but some coastal areas will be windy as well with the
passage of the cold front Thursday. Some light precipitation will
occur Friday mostly along the coastal mountain slopes, then another
system will bring showers Saturday afternoon and evening, but with
light to moderate precipitation amounts along with chilly weather.
After a few days of fair weather with a warming trend, another storm
system could move through the region Wednesday or Thursday of next
week.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Skies were mostly cloudy this evening with a few sprinkles. Models
are trending less with precip overnight, but significant rainfall is
likely to move through the area from northwest to southeast with a
cold front Thursday. Timing of heaviest rain appears to be early-mid
morning from Orange County through the Inland Empire to SBD County
Mountains, and late morning/early afternoon in San Diego County and
the mountains of Riverside County. With moisture up to around 650 MB
and 30-50 knots winds in the 700-850 MB layer from the
west/southwest, there should be substantial orographic precipitation
on W/SW facing mountains slopes. The trough axis will follow the
front and mostly move over Thursday evening, so a second peak in the
heavier precipitation is likely then. Rainfall totals through
Thursday night still appear to be:
Lower deserts: 0.30 inches or less.
High deserts: 0.25 to 0.50 inches
Coast: 0.75 to 1.25 inches
Valleys: 1.00 to 1.75 inches
Mountains: 1.50 to 5.00 inches (highest on coastal slopes)
If thunderstorms form, there could be heavy rainfall rates easily
over 1/2 inch per hour. Also, there is a lot of directional wind
shear along and ahead of the front along with surface CAPE values
around 400 J/kg, which could contribute to waterspouts, or perhaps
even a brief isolated weak tornado, though confidence is quite low
on that. More likely there will be strong gusty winds along the
front, with gusts near the coast possibly over 40 MPH, of course
much higher over the mountains where local gusts could exceed 60 MPH.
Snow levels will be quite high, above 8000 feet, Thursday morning
but should come down somewhat. 00Z NAM has wet bulb zero getting
only down to around 6000 feet though, so the snow level may stay at
or even a little above 6000 feet Thursday night. In the colder air
above the snow level, there could be significant snow, 4-12 inches
at/above 7000 feet, locally higher at highest peaks.
After the storm passes to the east, there remains some low-level
moisture and fairly strong onshore flow, so a few showers could
occur along the coastal mountain slopes Friday and Friday night.
Another system is still on track to move through the area Saturday
afternoon/evening, but most rainfall from this should be below 1/2
inch, except locally over an inch could occur on west-facing
mountain slopes (more northerly low-level wind profile due to the
more inland track of the upper low). It will be a colder system,
with a snow level possibly 5000 feet or less, so several inches of
snow could fall in the mountains. It will be quite chilly, with
highs Saturday barely above 60 at lower elevations, and after the
system moves through, Sunday should have a cold air mass overhead,
with temps likely not getting much above 60 then. Warmer weather
should return Mon/Tue, though models are showing some kind of
Pacific storm system, possibly strong, moving through Wed/Thu.
&&
.AVIATION...
290430Z...
Coast/Valleys/Mountains...Ceilings will lower across the
terminals west of the mountains tonight. Light showers are
developing over the coastal waters this evening and will spread
inland beginning around 06Z. Expect widespread rain with ceilings of
1500-2200 ft MSL and visibilities 3-5SM beginning late tonight. Cold
front will approach KSNA/KONT around 15Z, KCRQ 18-19Z, and KSAN 20-
21Z. The window for heaviest rainfall and isolated thunderstorms
will begin about 3 hours before the frontal passage. In the heavier
band visibilities could be reduced to 1SM with wind gusts 20-30
knots with local gusts to 35 knots possible. In the wake of the
front ceilings will improve to 3000-4000 ft MSL. However, another
round of showers is likely to impact the terminals Thursday evening
in the wake of the front. Frequent wind gusts of 25-30 knots are
likely Thursday afternoon/evening.
Deserts...VFR conditions are expected tonight. Scattered showers and
isolated thunderstorms are expected Thursday as a cold front moves
across the area. Rain could reduce visibilties at times. Wind gusts
of 25-35 knots are likely beginning around 20Z Thursday in the wake
of the front.
&&
.MARINE...
An approaching storm system will generate strong winds and rough
seas beginning late tonight. A cold front will cross the coastal
waters Thursday with wind gusts to 30 knots possible through Friday.
In addition, a few thunderstorms will be possible Thursday afternoon
and evening. Winds will decrease some late Friday. A Small Craft
Advisory is in effect from late tonight through Friday. Hazardous
conditions will be possible again late Saturday through Sunday
across the coastal waters.
&&
.BEACHES...
A long-period swell from the west-northwest will continue to
generate high surf starting today. The surf will peak Thursday into
Friday before gradually subsiding over the weekend. For details,
check the High Surf Advisory and the Surf Zone Forecast.
&&
.HYDROLOGY...
A few showers will occur overnight, producing mostly under 1/10
inch, except late on the south slopes of the San Bernardino County
Mountains.
From previous discussion (little change in general prognosis)...
More widespread and heavier rainfall is expected with the cold front
as it moves through southwest California Thursday morning and early
afternoon. Isolated thunderstorms are possible with the cold frontal
passage. Rainfall rates of one half to one inch per hour will be
possible with heavier showers and thunderstorms. Rainfall rates of
around one half inch per hour will be possible on southwest facing
mountain slopes. These rainfall rates are capable of causing local
urban flooding, ponding of water in poorly drained areas, and deadly
mud slides and debris flows on and below recent burn areas. The
Flash Flood Watch for recent burn areas has been extended and now
goes from Thursday morning through late Thursday night.
After the front passes, periods of showers with isolated
thunderstorms will continue through Thursday night, with showers
decreasing early Friday morning. Through early Friday, rainfall
is expected to range from around one inch near the coast to 2 to 4
inches in the mountains. Isolated rainfall totals of around 5
inches will be possible on favored southwest facing slopes. Around
one half inch of rainfall is expected in the high desert areas
and one tenth to one quarter inch in the lower deserts.
A second, weaker storm may bring additional showers to portions of
Southern California for Saturday afternoon into Sunday with less
rainfall expected.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 6 AM Thursday to 6 AM PST Friday for Apple
and Lucerne Valleys-Riverside County Mountains-San
Bernardino County Mountains-San Diego County Deserts-San
Diego County Mountains-San Gorgonio Pass Near Banning.
Winter Weather Advisory from noon Thursday to 2 AM PST Friday
for Riverside County Mountains-San Bernardino County
Mountains.
Flash Flood Watch from Thursday morning through late Thursday
night for Orange County Inland Areas-Riverside County
Mountains-San Bernardino County Mountains-Santa Ana
Mountains and Foothills.
Wind Advisory from 8 AM to 6 PM PST Thursday for Orange County
Coastal Areas-Orange County Inland Areas-San Bernardino and
Riverside County Valleys-The Inland Empire-San Diego County
Coastal Areas-San Diego County Valleys-Santa Ana Mountains
and Foothills.
High Surf Advisory until 8 PM PST Saturday for San Diego County
Coastal Areas.
High Surf Advisory until 10 PM PST Friday for Orange County
Coastal Areas.
PZ...Small Craft Advisory from 4 AM Thursday to 10 PM PST Friday for
Coastal Waters from San Mateo Point to the Mexican Border
and out to 30 nm-Waters from San Mateo point to the Mexican
Border Extending 30 to 60 nm out including San Clemente
Island.
&&
PUBLIC/HYDROLOGY...Maxwell
AVIATION/MARINE/BEACHES...MorelandThe Santa Ana Mts radar (KSOX), 45 km away, was scanning. The volume nearest the first event began at 08:01 UTC.
5 debris flow, 4 high wind, 3 heavy rain, 3 flash flood. Local standard time, as filed.
Mesonet ssvc1 (8 mi nne of Rancho Cucamonga) reported a 24-hr rainfall total of 3.38 inches.
CoCoRaHS station ca-sr-63 in Crestline reported a 24-hr rainfall total of 3.6 inches.
Santiago Peak 2 mesonet reported a 24-hr rain total of 3.24 inches.
Mormon Rock Mesonet reported a peak wind gust of 61 knots between 0100 and 0200 PST on November 29th.
Whitewater raws mesonet reported a peak wind gust of 52 knots between 0700 and 0800 PST on November 30th.
Heaps Peak mesonet reported a peak wind gust of 57 knots between 0800 and 0900 PST on November 29th.
Media reported highway 60 (Pomona Ave.) at Etiwanda Ave. was flooded due to heavy rain with accidents reported in the area.
Burns Canyon mesonet reported a peak wind gust of 54 knots between 0900 and 1000 PST on November 29th.
California Highway Patrol reported a vehicle stuck in approximately 1 foot of standing water along Highway 210. No injuries were reported.
A spotter reported a significant gray water flow in Horsethief Canyon within the canyon banks. No injuries or damages were reported.
Department of Highways reported a road closure due to flooding on Verdemont and Cajon Blvd.
Media reported major debris flow in Trabuco Canyon. The debris flow appeared to be mainly comprised of very little water and mostly mud/rocks.
CalFire reported water and debris from Coldwater Canyon flowing over into Glen Ivy Road.
CalTrans reported an emergency closure of SR-38 at Valley of the Falls Drive due to a debris flow.
Riverside County Emergency Management reported water and rocks in the road near Temescal Canyon.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, November 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: 793345, 793350, 793355, 793359, 793344, 793343, 793339, 793358, 793341, 793351, 793353, 793352, 793354, 793356, 793357.