In mid-December, a large upper level low pressure system developed over the northeastern Pacific Ocean. This low pressure system tapped into a subtropical moisture source, bringing an extended period of significant rainfall to Central and Southern California from the 17th through the 22nd.
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 LOX wrote it up.
In mid-December, a large upper level low pressure system developed over the northeastern Pacific Ocean. This low pressure system tapped into a subtropical moisture source, bringing an extended period of significant rainfall to Central and Southern California from the 17th through the 22nd. Numerous daily rainfall records were set during the period. By the end of the event, rainfall totals ranged from 5 to 10 inches across coastal areas to between 10 and 18 inches in the foothills and mountains with even local amounts as high as 24 inches. With such significant rainfall, numerous reports of flooding were reported across the area, including several mountain roads being washed out. Due to the subtropical nature of the air mass, snow levels remained rather high through the event although between 12 and 24 inches of snow fell at resort level.
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 Dec 20, 8:00 PM PST, 0 minutes earlier.
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 800 PM PST MON DEC 20 2010 .SYNOPSIS... A COLD UPPER LEVEL LOW PRESSURE SYSTEM OFF THE OREGON COAST WILL CONTINUE TO STEER DEEP SUBTROPICAL MOISTURE INTO SOUTHERN CALIFORNIA THROUGH WEDNESDAY...BRINGING PERIODS OF RAIN AND HIGHER ELEVATION SNOW. AS THE MAIN COLD FRONT MOVES THROUGH THE REGION...THERE WILL BE A GREATER THREAT FOR HEAVIER RAIN AND THUNDERSTORMS TUESDAY NIGHT INTO WEDNESDAY. DRIER WEATHER WILL PREVAIL THURSDAY INTO FRIDAY...FOLLOWED BY ANOTHER CHANCE OF LIGHT RAIN ON CHRISTMAS DAY. && .SHORT TERM (TONIGHT-THU)... FORECAST IS LOOKING GOOD AND ON TRACK. AXIS OF GREATEST RAIN IS OVER EASTERN L.A. COUNTY WHERE STRONG SW WINDS ARE CREATING VERY GOOD UPSLOPE RAINS. OVER THE LAST 4 HOURS AN INCH OF RAIN HAS FALLEN OVER THE FOOTHILLS AND OVER TWO INCHES IN THE MTNS WITH A QUARTER TO HALF INCH AMOUNTS OVER THE FLATTER COASTAL AND VLY LOCATIONS. FLASH FLOOD WARNING BASED ON VERY HIGH RAINFALL NUMBERS AT TANBARK WILL LIKELY8 EXPIRE AS THE MAIN BAND OF RAIN IS SHIFTING OUT OF THE COUNTY INTO SAN BERNARDINO COUNTY. SOUTH WINDS ARE A LITTLE STRONGER THAN FCST AND WILL BE BUMPING THEM UP IN AN UPDATE. A QUICK LOOK AT THE 00Z MDLS SHOWS THAT EVERYTHING IS STILL ON TRACK. LOOK FOR A LITTLE LULL OVERNIGHT AND MOST OF TUESDAY. THERE WILL STILL BE ON AND OFF RAIN BUT AMOUNTS WILL BE MOSTLY LIGHT THEN THE FRONT WILL MOVE ON THROUGH TUE NIGHT AND WEDNESDAY BRING VERY HEAVY RAIN AND SCATTERED THUNDERSTORMS. THIS WILL BE A VERY DANGEROUS TIME GIVEN ALL OF THE ANTECEDENT RAIN. THE WINTER CONDITIONS WILL BE VERY TRICKY AS THERE IS A SHARP DECREASE IN SNOW LEVEL AS ONE MOVES FROM SOUTH TO NORTH. SNOW ELEVATIONS CURRENTLY RANGE FROM AROUND 7500 FEET OVER THE COASTAL SLOPES TO 5000 FEET NEAR THE GRAPEVINE. LATEST NAM HAS A LITTLE LESS WINDS SO THE COASTS AND THE VLY MAY BE SPARED ADVISORY LEVEL WIND SPEEDS ALTHOUGH IT WILL BE BREEZY. ...FROM PREVIOUS DISCUSSION... COLD UPPER LEVEL LOW PRESSURE SYSTEM CENTERED OFF THE OREGON COAST CONTINUES TO STEER A RICH SUPPLY OF SUBTROPICAL MOISTURE INTO CENTRAL AND SOUTHERN CALIFORNIA. WITHIN THE PAST COUPLE OF HOURS...THE MOISTURE PLUME HAS TAKEN ON A MORE SOUTHWEST-NORTHEAST ORIENTATION WITH THE FOCUS OF DEEPEST MOISTURE OCCURRING FROM LOS ANGELES COUNTY SOUTHWARD. IN FACT...LATEST SATELLITE IMAGERY SHOWING A RESURGENCE OF PW VALUES...WITH A MAX VALUE OF 1.4 INCHES BETWEEN LOS ANGELES AND SAN DIEGO. IN ADDITION...LATEST 18Z NAM SHOWING A STRENGTHENING OF LOW LEVEL SOUTH TO SOUTHWEST WINDS THAT WILL HELP TO BRING SOME STRONG OROGRAPHIC ENHANCEMENT ACROSS LA AND SAN BERNARDINO COUNTIES THROUGH THE EVENING HOURS. LATEST DOPPLER RADAR IMAGERY SHOWING THIS TREND WITH MODERATE TO LOCALLY HEAVY RAINFALL ACROSS MUCH OF LOS ANGELES COUNTY AS OF 2 PM. FLOOD ADVISORY CURRENTLY IN EFFECT FOR LOS ANGELES COUNTY...AS A LARGE AREA OF RAINFALL RATES BETWEEN .25 AND .50 INCHES HAS BEEN OBSERVED ACROSS THE LA BASIN...WITH RATES BETWEEN .50 AND .75 INCHES OBSERVED ACROSS THE SAN GABRIEL MOUNTAINS. RAINFALL RATES ARE EXPECTED TO GRADUALLY DIMINISH LATER TONIGHT AND MUCH OF THE DAY TUESDAY...HOWEVER MAIN COLD FRONT IS EXPECTED TO BRING A RESURGENCE OF HEAVIER RAINFALL INTO CENTRAL AND SOUTHERN CALIFORNIA LATER TUESDAY NIGHT INTO WEDNESDAY MORNING. WHEN THIS MAIN FRONT PUSHES THROUGH THE REGION...THERE IS A SHARP INCREASE IN LOW LEVEL SOUTHERLY FLOW...WITH TIME HEIGHT CROSS SECTIONS SHOWING A LARGE AREA OF 40-50 KNOT WINDS IN THE BOUNDARY LAYER. THIS STRONG SOUTHERLY FLOW WILL ONCE AGAIN BRING AN AREA OF STRONG OROGRAPHIC ENHANCEMENT TO SOUTH FACING SLOPES. IN ADDITION...THIS PORTION OF THE SYSTEM WILL HAVE STRONGER DYNAMICS IN ASSOCIATION WITH A 100 KNOT JET AND ASSOCIATED UPPER LEVEL DIVERGENCE. LAST BUT NOT LEAST...THERE IS BETTER CONVECTIVE POTENTIAL LATER TUESDAY NIGHT INTO WEDNESDAY IN ASSOCIATION WITH COLDER AIR ALOFT AND BETTER UPPER LEVEL DYNAMICS. IN FACT...18Z NAM CONTINUES TO ADVERTISE A LARGE AREA OF LIFTED INDEX VALUES BETWEEN 0 AND -2 ACROSS THE CWA FROM LATE TUESDAY NIGHT INTO WEDNESDAY. AT THIS TIME...IT APPEARS THAT THE GREATEST THREAT FOR HEAVIEST RAINFALL AND THUNDERSTORMS WILL BE LATER TUESDAY NIGHT INTO WEDNESDAY MORNING...WHEN LOCAL RAINFALL RATES COULD EXCEED ONE INCH PER HOUR. ADDITIONAL RAINFALL TOTALS FROM TODAY THROUGH WEDNESDAY ARE GENERALLY EXPECTED TO BE HIGHEST SOUTH OF POINT CONCEPTION...WHERE 2 TO 4 INCHES WILL BE COMMON FOR COASTAL/VALLEY AREAS...AND 4 TO 8 INCHES FOR FOOTHILLS AND MOUNTAINS...EXCEPT ISOLATED TOTALS UP TO 10 INCHES ACROSS THE EASTERN SAN GABRIELS. SINCE TUESDAY NIGHT INTO WEDNESDAY WILL BE MORE CONVECTIVE IN NATURE...WE COULD SEE THE HIGHEST RAINFALL RATES SO FAR. THIS WILL BE AN ESPECIALLY PRECARIOUS TIME FOR THE BURN AREAS...ESPECIALLY IN LOS ANGELES COUNTY. INTENSE RAINFALL RATES ON TOP OF THOROUGHLY SOAKED GROUNDS WILL THE BRING THE POTENTIAL FOR DANGEROUS FLASH FLOODING AND DEBRIS FLOWS IN THE RECENT BURN AREAS. IN FACT IF HIGH INTENSITY UPSLOPE OR THUNDERSTORM RAINS DEVELOP THERE MAY WELL BE FLASH FLOODING NOT ASSOCIATED WITH BURN AREAS...AND LATER SHIFTS MAY NEED TO EXPAND THE FLASH FLOOD WATCH FOR NON-BURN AREAS AS WELL. OTHER KEY ISSUES WITH THIS SYSTEM WILL BE SNOW AND WINDS. WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR THE MOUNTAINS OF VENTURA AND SANTA BARBARA COUNTIES THROUGH TUESDAY...WITH SNOW LEVELS GENERALLY RANGING BETWEEN 5000 AND 6000 FEET...HIGHER IN LOS ANGELES COUNTY. THESE AREAS COULD SEE SNOW ACCUMULATIONS BETWEEN 4 AND 7 INCHES THROUGH TUESDAY. SINCE THERE IS THE POTENTIAL FOR HEAVIER SNOW AND STRONGER WINDS TUESDAY NIGHT INTO WEDNESDAY...A WINTER STORM WATCH HAS BEEN POSTED FOR THE MOUNTAINS OF LOS ANGELES AND VENTURA COUNTIES FOR THIS TIME FRAME. THE MOST SIGNIFICANT ACCUMULATIONS ARE EXPECTED ABOVE 6000 FEET DURING THIS TIME...GENERALLY IN THE 1 TO 2 FOOT RANGE...BUT LOWER ELEVATIONS COULD SEE LIGHTER ACCUMULATIONS. THE STRONGEST WINDS ARE EXPECTED TUESDAY NIGHT...WHEN WE COULD SEE SOUTHERLY WINDS GUSTING TO 60 MPH IN THE MOUNTAINS. A HIGH WIND WATCH HAS ALSO BEEN POSTED FOR THE SBA COUNTY MOUNTAINS. AS WE DRAW CLOSER TO THE EVENT...WIND ADVISORIES WILL LIKELY BE REQUIRED FOR MANY OTHER ZONES ACROSS THE REGION ON TUESDAY NIGHT WITH GUSTS BETWEEN 30 AND 40 MPH COMMON. CHANCE OF LINGERING SHOWERS WEDNESDAY NIGHT...FOLLOWED BY DRY WEATHER ON THURSDAY. .LONG TERM (FRI-MON)... DRY CONDITIONS EXPECTED ON FRIDAY WITH WARMING TREND. ANOTHER WEATHER SYSTEM COULD BRING A CHANCE OF RAIN FOR CHRISTMAS DAY. AT THIS POINT IT LOOKS LIKE WE WILL BE ON THE SOUTHERN END OF THIS COLD FRONT...WITH RAIN SPREADING INTO SLO/SBA COUNTIES ON CHRISTMAS DAY AND WEAKENING AS IT MOVES INTO LA/VTU COUNTIES CHRISTMAS NIGHT. SLIGHT CHANCE OF A LIGHT SHOWERS FOR REMAINDER OF EXTENDED PERIOD. && .AVIATION...20/2350Z. TWO MAIN RAIN BANDS CURRENTLY MOVING ACROSS THE AREA. THE HEAVIEST BAND IS OVER EASTERN LAX COUNTY...WITH A LESS INTENSE BAND OVER SLO/SBA COUNTIES. CIGS/VSBYS WILL LIKELY VARY GREATLY FROM HOUR TO HOUR...SO CONFIDENCE IN 00Z TAF IS LOW. KLAX...LOW CONFIDENCE IN 00Z TAF. KBUR...LOW CONFIDENCE IN 00Z TAF. && .LOX WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY (SEE LAXWSWLOX). FLOOD WATCH (SEE LAXFFALOX). WINTER STORM WATCH (SEE LAXWSWLOX) HIGH RIP CURRENT RISK (SEE LAXSRFLOX). SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && PUBLIC...GOMBERG/ASR AVIATION...THOMPSON SYNOPSIS...GOMBERG WWW.WEATHER.GOV/LOSANGELES
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 255 PM PST MON DEC 20 2010 CAZ034>041-044>046-051>054-059-087-088-547-548-211400- SAN LUIS OBISPO COUNTY CENTRAL COAST- SANTA BARBARA COUNTY CENTRAL COAST-SANTA YNEZ VALLEY- SAN LUIS OBISPO COUNTY INTERIOR VALLEYS-CUYAMA VALLEY- SANTA BARBARA COUNTY SOUTH COAST-VENTURA COUNTY COAST- LOS ANGELES COUNTY COAST INCLUDING DOWNTOWN LOS ANGELES- VENTURA COUNTY INTERIOR VALLEYS-VENTURA COUNTY COASTAL VALLEYS- SANTA MONICA MOUNTAINS RECREATIONAL AREA- SAN LUIS OBISPO COUNTY MOUNTAINS- SANTA BARBARA COUNTY MOUNTAINS-VENTURA COUNTY MOUNTAINS- LOS ANGELES COUNTY MOUNTAINS EXCLUDING THE SANTA MONICA RANGE- ANTELOPE VALLEY-CATALINA ISLAND-SANTA CLARITA VALLEY- LOS ANGELES COUNTY SAN FERNANDO VALLEY- LOS ANGELES COUNTY SAN GABRIEL VALLEY- 255 PM PST MON DEC 20 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWESTERN CALIFORNIA. .DAY ONE... THROUGH TONIGHT PERIODS OF RAIN WILL CONTINUE ACROSS THE AREA THROUGH TONIGHT. THE HEAVY RAINFALL WILL PRODUCE LOCAL NUISANCE FLOODING OF LOW LYING AREAS SUCH AS UNDERPASSES. FOR THE RECENT BURN AREAS...THERE IS THE POTENTIAL FOR HIGH RAINFALL RATES WHICH COULD PRODUCE MUD AND DEBRIS FLOWS. LOWERED SNOW LEVELS HAVE BROUGHT LIGHT TO MODERATE SNOWFALL TO THE MOUNTAINS ABOVE 5000 FEET ELEVATION OF VENTURA AND SANTA BARBARA COUNTIES...AND WILL CONTINUE THROUGH AT LEAST TONIGHT WHILE SPREADING INTO THE LOS ANGELES COUNTY MOUNTAINS. BEACH GOERS WILL FACE AN ENHANCED RISK OF RIP CURRENTS. * FLASH FLOOD WATCH..........SEE WGUS66 KLOX - FFALOX FOR DETAILS * * WINTER WEATHER ADVISORY....SEE WWUS46 KLOX - WSWLOX FOR DETAILS * * HIGH RIP CURRENT RISK......SEE FZUS56 KLOX - SRFLOX FOR DETAILS * .DAYS TWO THROUGH SEVEN... TUESDAY THROUGH SUNDAY THE WET PATTERN IS EXPECTED TO CONTINUE ACROSS THE AREA THROUGH WEDNESDAY. THE ADDITIONAL RAINFALL WILL CONTINUE TO BRING DRIVING AND FLOODING ISSUES TO THE AREA. SNOW ACCUMULATIONS WILL INCREASE ABOVE 6000 FEET ELEVATION TUESDAY AND WEDNESDAY WITH SIGNIFICANT SNOWFALL EXPECTED TUESDAY NIGHT AND WEDNESDAY. STRONG SOUTHERLY WINDS WILL LIKELY IMPACT THE MOUNTAIN TUESDAY NIGHT...WITH DAMAGING GUSTS POSSIBLE. THERE WILL ALSO BE THE THREAT OF THUNDERSTORMS EVERYWHERE TUESDAY NIGHT AND WEDNESDAY. DRY CONDITIONS ARE EXPECTED ON THURSDAY AND FRIDAY. BY LATE CHRISTMAS DAY...ANOTHER BUT MUCH WEAKER STORM SYSTEM IS EXPECTED TO APPROACH SAN LUIS OBISPO COUNTY...BRINGING A POSSIBILITY OF RAIN TO ALL AREAS BY SUNDAY. * HIGH WIND WATCH............SEE WWUS76 KLOX - NPWLOX FOR DETAILS * * FLASH FLOOD WATCH..........SEE WGUS66 KLOX - FFALOX FOR DETAILS * * WINTER STORM WATCH.........SEE WWUS46 KLOX - WSWLOX FOR DETAILS * * WINTER WEATHER ADVISORY....SEE WWUS46 KLOX - WSWLOX FOR DETAILS * .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. SIRARD
The Santa Ana Mts radar (KSOX), 61 km away, was scanning. The volume nearest the first event began at 04:00 UTC.
3 flash flood, 2 winter storm. Local standard time, as filed.
A weather spotter reported flash flooding and debris flow near the community of Wrightwood. Flume Canyon Road near the intersection with the Angeles Crest Highway was completely washed out by the heavy rainfall.
Heavy showers produced significant flash flooding in south central Los Angeles County. California Highway Patrol reported significant flooding at the intersection of Vermont Avenue and West 190th Street with over one foot of water and numerous vehicles stalled in the high water.
Heavy rainfall produced flash flooding in the mountains of Los Angeles County. California Highway Patrol reported that Big Rock Creek Road at the intersection of the Angeles Crest Highway was washed out by flash flooding and mud flows.
Significant snowfall was received at the resort level (above 7000 feet) across the mountains of Los Angeles County. Mountain High resort reported between 12 and 24 inches of new snowfall. Along with the snowfall, southeasterly winds gusted between 45 and 55 MPH and produced dangerous winter storm conditions.
Significant snowfall was received at the resort level (above 7000 feet) across the mountains of Ventura County. Based on surrounding reports, high elevation areas received over 12 inches of snowfall. Along with the snowfall, southeasterly winds gusted between 45 and 55 MPH and produced dangerous winter storm conditions.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2010Every state in 2010This day in weather historyWarnings in California, December 2010
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: 266931, 266934, 266935, 266932, 266933.