Strong thunderstorms moved over the Los Angeles county area, bringing heavy rain to the area. Near the Fish burn scar, the heavy rain produced flash flooding and mud and debris flows in the city of Azusa.
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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 LOX wrote it up.
Strong thunderstorms moved over the Los Angeles county area, bringing heavy rain to the area. Near the Fish burn scar, the heavy rain produced flash flooding and mud and debris flows in the city of Azusa.
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 Los Angeles, CA wrote its last area forecast discussion before the first event at Jan 12, 2:01 PM PST, 40 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
201 PM PST Thu Jan 12 2017
.SYNOPSIS...
A cold low pressure system will affect the region today with
periods of rain, mountain snow, and possible thunderstorms. Some
rain and mountain snow showers will continue over the mountains
into Friday. Otherwise, dry and increasingly mild weather will
prevail Friday through early next week as high pressure builds in.
The next chance for rain will be the middle of next week.
&&
.SHORT TERM...(TDY-SUN)
The front has moved into Los Angeles County and the heaviest
precipitation is now across the eastern portion of the county.
There was little to no break between the frontal rain and the
lingering warm flow rain that had been falling in the area since
the overnight hours. This has resulted in some very soggy soils
and a flash flood watch continues in portions of the county
through late evening. A flash flood warning is in effect for the
burn areas of northeastern Los Angeles County as a band of heavy
showers are poised to move over the area through mid afternoon.
Behind the front conditions are more spotty/showery and as the
colder air mass slides southward it is this precipitation that
brings the threat of snow to mountain locations. Radar and spotter
reports indicate that snow was sticking down to near 5000 feet in
some locations with flurries down a bit lower. The coldest air
will not move directly over the mountains today but rather will
remain off the coast with the low center until the low moves
inland over Orange and San Diego Counties. The coldest air will
move across the area mountains with the low passage but most of
the precipitation will be over at that time. Some snowfall is
expected overnight on the Grapevine and other passes around 3500
feet and higher but the greatest danger will be the wet roads
icing over and then perhaps getting snow on top. This is typically
more dangerous than just snow on the roads.
The combination of very cold air coming in behind the front and
good jet dynamics to the south of Los Angeles County help to
increase the instability across the county this afternoon. There
have been a few reports of thunder in Los Angeles County along
the front... but conditions look to be more unstable by mid
afternoon as solar heating adds a bit more instability to the
mix. Thunderstorm development will likely be isolated. However in
such a moist environment this could still result in a heavy burst
of additional rainfall to soggy locations. The greatest threat
will be from mid afternoon through early evening.
As the low center slides south of Los Angeles County and then
eastward... there will likely be some wrap around moisture that
adds some final precipitation to the San Gabriel Mountains and
perhaps to the Antelope Valley. Otherwise the precipitation exits
the region Friday afternoon. A weak offshore flow sets up on
Saturday and this will give a warming kick to the region and
temperatures will be near normal by Sunday.
.LONG TERM...(MON-THU)
Conditions will be relatively warm and dry across the region
through Wednesday. Another strong weather system will approach
southwestern California by early Thursday... possibly in San Luis
Obispo County by late Wednesday. At this time the heavist rain
looks to be a midday Thursday through Friday event. Still pretty
far out in time but it looks promising.
&&
.AVIATION...12/1800Z.
At 1800Z, there was no marine inversion present at KLAX.
Very low confidence in all TAFs. There will be frequent cig and
vis category changes through the day. MVFR cigs and vis will be
the most common with IFR conds second most common. The rain will
exit SLO and SBA counties this afternoon and then Ventura and LA
counties this evening. There is a 20 percent chc of a TSTM over
L.A. county 20Z-02Z.
KLAX...Very low confidence in the 18z TAF. There will be frequent
cig and vis category changes through the day. MVFR cigs and vis
will be the most common with IFR conds second most common. There
is a 60 percent chc that the east winds will not exceed 7 knots
this morning. There is a 20 percent chc of a TSTM 20Z-02Z.
KBUR...Very low confidence in the 18z TAF. There will be frequent
cig and vis category changes through the day. MVFR cigs and vis
will be the most common with IFR conds second most common. There
is a 20 percent chc of a TSTM 20Z-02Z.
&&
.MARINE...12/200 PM.
A storm system passing through the coastal waters today will
increase winds to SCA criteria for the outer waters mainly
northwest of the Channel Islands, with winds approaching SCA
levels elsewhere by this afternoon and persisting for the next
couple of days. There will also be a slight chance of
thunderstorms over the inner waters s of Point Mugu for this afternoon.
There is a 40% chance for some SCA level gusts Fri-Sat...with a
better chance for SCA level winds by Saturday afternoon across the
outer waters.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement in effect through Friday morning for
zones 39>41-87. (See LAXCFWLOX).
Winter Weather Advisory in effect until 9 AM PST Friday for
zones 52>54. (See LAXWSWLOX).
Flash Flood Watch in effect until 9 PM PST this evening for
zones 54-88. (See LAXFFALOX).
PZ...Small Craft Advisory for winds in effect until 9 PM PST this
evening for zones 670-673. (See LAXMWWLOX).
&&
.HAZARD POTENTIAL OUTLOOK...(SUN-THU)
Another strong weather system may begin to affect the region by Thursday.
&&
PUBLIC...Kj
AVIATION...Sweet
MARINE...Sweet
SYNOPSIS...Sukup
weather.gov/losangelesThe Santa Ana Mts radar (KSOX), 46 km away, was scanning. The volume nearest the first event began at 22:39 UTC.
1 flash flood. Local standard time, as filed.
Strong thunderstorms brought heavy rain to the Fish burn scar. The heavy rain produced mud and debris flows which impacted Encanto Parkway in the city of Azusa.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2017Every state in 2017This day in weather historyWarnings in California, January 2017
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: 677801.