241
FXUS66 KLOX 150658
AFDLOX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1058 PM PST SAT FEB 14 2026
SYNOPSIS
14/656 PM.
DRY CONDITIONS AND SEASONABLE TEMPERATURES ARE EXPECTED THROUGH
SUNDAY. THEN, A POWERFUL STORM SYSTEM WILL AFFECT THE REGION
STARTING MONDAY, BRINGING THE POTENTIAL FOR SEVERE THUNDERSTORMS,
BURN-SCAR DEBRIS FLOWS, FLASH FLOODING WITH ROCK AND MUD SLIDES,
DAMAGING WINDS, HEAVY MOUNTAIN SNOW, AND HIGH SURF WITH COASTAL
FLOODING. COLD AND BLUSTERY CONDITIONS WITH PERIODIC RAIN
WILL OCCUR THROUGH AT LEAST THE MIDDLE OF THIS COMING WEEK.
SHORT TERM (SAT-TUE)
14/913 PM.
***UPDATE***
QUIET BEFORE THE STORM THIS EVENING. A MIX OF LOW AND HIGH CLOUDS
WILL LIKELY FILL IN OVERNIGHT WITH BREEZY BUT MOSTLY SUB-ADVISORY
SOUTHERLY WINDS.
SUNDAY AFTERNOON THROUGH EVENING WE MAY BEGIN SEEING LOW TOPPED
CONVECTIVE SHOWERS FOCUSED ACROSS NORTHERN AREAS. THEY WILL BE ON
THE MOVE, LIMITING THE THREAT OF MINOR FLOODING, ESPECIALLY
CONSIDERED THE VERY DRY SOILS. LOOKS LIKE THE AN INITIAL THREAT OF
ISOLATED THUNDERSTORMS COULD ARRIVE AS EARLY AS SUNDAY NIGHT NORTH
OF POINT CONCEPTION.
PART ONE OF THE PROLONGED PERIOD OF UNSETTLED WEATHER IS SHOWING
SIGNS OF SPEEDING UP SLIGHTLY PER LATEST GUIDANCE. SUITE OF
WINTER, WIND, AND FLOOD HAZARDS LOOK GOOD FOR NOW, BUT IF THE
SYSTEM CONTINUES TO SPEED UP, SOME HAZARDS MAY NEED TO BE MOVED
EARLIER.
SEVERE WEATHER LOOKS ON TRACK TO BELOWS DISCUSSION WITH MONDAY
NOW FULLY WITHIN THE REFS WINDOW. SHOULD INSTABILITY BE ON THE
UPPER END OF THE POTENTIAL ENVELOPE, DAMAGING WIND GUSTS OF 60+
MPH WILL BE POSSIBLE WITHIN STRONGER BOWING SEGMENTS OF THE SQUALL
LINE ANTICIPATED MAINLY MONDAY MORNING TO AFTERNOON AND MAINLY
SOUTH OF POINT CONCEPTION. A RARE COMBINATION OF LOW LEVEL SHEAR
AND SPIN WITH QUESTIONABLE BUT POTENTIALLY ADEQUATE INSTABILITY
WILL MAY SUPPORT A COUPLE OF BRIEF TORNADOES. FLOW ALOFT MORE
SOUTHERLY THAN TYPICAL FOR OUR SEVERE WEATHER SETUPS MAY SUPPORT
ANY TORNADOES BEING FURTHER WEST IN COASTAL BASINS AND CLOSER TO
THE COAST THAN IS USUAL.
***FROM PREVIOUS DISCUSSION***
DRY CONDITIONS, SEASONABLE TO SLIGHTLY ABOVE-NORMAL TEMPERATURES,
AND INCREASING CLOUDS ARE EXPECTED THIS WEEKEND, AS AN UPPER
RIDGE TRANSITS THE FORECAST AREA AND A MAJOR STORM SYSTEM
APPROACHES FROM THE WEST.
A POWERFUL STORM SYSTEM WILL BRING MULTIPLE MODES OF POTENTIALLY
DANGEROUS WEATHER TO SOUTHERN CALIFORNIA ON MONDAY --
POSSIBILITIES RANGING FROM SEVERE THUNDERSTORMS AND PERHAPS A
COUPLE OF WEAK TORNADOES, TO BURN-SCAR DEBRIS FLOWS, TO FLASH
FLOODING WITH ROCK AND MUD SLIDES, TO DAMAGING GRADIENT WINDS, TO
HEAVY MOUNTAIN SNOW, AND VERY HIGH SURF WITH COASTAL FLOODING.
OVERALL, THE LARGE-SCALE SYNOPTIC PATTERN, AND ALREADY HINTS OF
THE MESOSCALE ENVIRONMENT, SUGGEST THAT SOME OF THESE HAZARDOUS-
WEATHER MODES COULD EVEN REACH EXTREME OR EVEN DESTRUCTIVE LEVELS
IN A FEW ISOLATED SPOTS, THOUGH UNCERTAIN.
AND BEFORE ADDRESSING DETAILS, IT IS IMPORTANT TO NOTE THAT NOT
ALL LOCATIONS WILL EXPERIENCE DANGEROUS WEATHER, AS THE FAST-
EVOLVING, CONVECTIVE, AND PROGRESSIVE NATURE OF THIS SYSTEM WILL
KEEP DANGEROUS WEATHER FAIRLY ISOLATED. NEVERTHELESS, INTERESTS
ACROSS THE LOCAL AREA ARE ENCOURAGED TO REMAIN AT A HIGH STATE OF
READINESS FOR DANGEROUS WEATHER CONDITIONS ON MONDAY. THE
CONVECTIVE ENVIRONMENT WILL BE CHARACTERIZED BY A LOW-CAPE, HIGH-
SHEAR PARAMETER SPACE, IN WHICH NONLINEAR FEEDBACKS INHERENT TO
UPDRAFT-SHEAR INTERACTIONS INFLUENCE THE SPECIFIC LOCATIONS,
TIMING, AND MAGNITUDES OF THE RELATIVELY-SPOTTY EXTREME WEATHER.
THESE FEEDBACKS ARE NOTORIOUSLY ACCOMPANIED BY LOW PREDICTABILITY,
SUCH THAT UNCERTAINTY IN THE DETAILS OF EXTREME IMPACTS -- IF
THEY WERE TO OCCUR -- COULD REMAIN SIGNIFICANT RIGHT UP UNTIL THE
ONSET OF SUCH IMPACTS, IF THEY WERE TO OCCUR. IN SHORT, THE
SYNOPTIC PATTERN WILL FAVOR THE POTENTIAL FOR DANGEROUS, AND EVEN
LIFE-THREATENING, WEATHER CONDITIONS TO OCCUR ON MONDAY, ANYWHERE
FROM THE TRANSVERSE RANGES SOUTHWARD TO THE PACIFIC COAST.
EVERYONE IS ENCOURAGED TO MONITOR THE LATEST INFORMATION FROM THE
NATIONAL WEATHER SERVICE IN LOS ANGELES/OXNARD, CALIFORNIA. FOLLOW
THE DIRECTION OF EMERGENCY MANAGEMENT AND LAW ENFORCEMENT
OFFICIALS AS THE SITUATION QUICKLY EVOLVES ON MONDAY. FLOOD
WATCHES, WINTER STORM WATCHES, HIGH WIND WATCHES, AND WIND
ADVISORIES HAVE BEEN POSTED FOR MONDAY. THE CONCLUSION OF THIS
SHORT TERM SECTION WILL BE FOLLOWED BY A TECHNICAL DISCUSSION
CONCERNING THE POTENTIALLY DANGEROUS WEATHER HAZARDS FOR MONDAY,
ALONG WITH SOURCES OF UNCERTAINTY, DETAILS ON IMPACTS, AND RANGES
OF FORECAST SCENARIOS.
BEYOND MONDAY, TUESDAY WILL FEATURE RELATIVELY LESS PRECIPITATION
AS THE FORECAST AREA IS POSITIONED BETWEEN LOBES OF ASCENT
TRAVERSING THE BASE OF CONUS-FULL-LATITUDE TROUGHING ANCHORED OVER
THE WEST. GIVEN THE PLACEMENT OF A SUB -20C 500-MB COLD CORE OVER
THE AREA, DIURNALLY ENHANCED CONVECTIVE PRECIPITATION AND
UPSLOPE-FLOW-FAVORED PRECIPITATION WILL CONTINUE, AND IT WILL BE
A BLUSTERY, COOL/COLD DAY. TEMPERATURES IN MOST AREAS WILL REMAIN
AT OR BELOW THE 50S. WHILE HIGH-ELEVATION SNOW WILL HAVE TAPERED
OFF TEMPORARILY BY TUESDAY, BLOWING/DRIFTING SNOW AND MUCH-
REDUCED VISIBILITIES WILL REMAIN OF CONCERN AND WINTER STORM
WATCHES WILL CONTINUE FOR THE EASTERN SAN GABRIELS AND NORTHERN
VENTURA COUNTY MOUNTAINS, THROUGH THE PASSAGE OF AN EVEN COLDER
PRECIPITATION-PRODUCING STORM SYSTEM TUESDAY NIGHT INTO
WEDNESDAY -- ADDRESSED IN THE LONG-TERM SECTION.
---TECHNICAL DISCUSSION FOR MONDAY WEATHER HAZARDS FOLLOWS---
*SEVERE THUNDERSTORMS AND PERHAPS A COUPLE OF TORNADOES:
WITHIN A HIGHLY AMPLIFIED FLOW PATTERN IN THE MID AND UPPER
LEVELS, IMPULSES OF SIGNIFICANT UPPER JET ENERGY DIGGING SOUTHWARD
FROM THE GULF OF ALASKA WILL BE CARVING OUT A LONGWAVE TROUGH
FROM LATE THIS WEEKEND AND INTO NEXT WEEK. A LEAD SHORTWAVE TROUGH
WILL ROUND THE BASE OF LARGER-SCALE BROAD CYCLONIC FLOW ON MONDAY
AND EJECT EAST-NORTHEASTWARD WITH A TRAJECTORY RIGHT OVER THE
LOCAL AREA, BECOMING PROMINENTLY NEGATIVELY TILTED DURING THE DAY
MONDAY. AN ACCOMPANYING 100-110-KT 500-MB, CYCLONICALLY-CURVED
SPEED MAXIMUM WILL RACE EAST-NORTHEASTWARD TOWARD THE CHANNEL
ISLANDS IN THE AFTERNOON, POSITIONING ITS LEFT-EXIT REGION AND
HIGHLY DIFFLUENT UPPER FLOW OVER THE BIGHT OF SOUTHERN CALIFORNIA.
THE ACCOMPANYING THERMALLY INDIRECT AGEOSTROPHIC CIRCULATION IN
THE EXIT REGION OF THE UPPER JET IS EXPECTED TO FACILITATE A
RELATIVELY DEEP LAYER OF LOW-LEVEL MASS RESPONSE, WITH AN INTENSE
LOW-LEVEL JET FORMING AND PROGRESSING ACROSS THE REGION ON MONDAY.
WITHIN THE WARM SECTOR OF THE CYCLONE, 850-700-MB SOUTHERLIES TO
SOUTHWESTERLIES IN CONJUNCTION THE LOW-LEVEL JET ARE FORECAST TO
REACH 45-65 KT. RELATED THERMAL ADVECTION WILL AUGMENT THE STRONG,
DEEP ASCENT TO FOSTER INTENSE CYCLOGENESIS FOR A NORTHEASTWARD-
TRACKING SURFACE LOW TOWARD THE CALIFORNIA CENTRAL COAST DURING
THE DAY ON MONDAY, DRIVING LAX-SFO ONSHORE PRESSURE GRADIENTS TO
AROUND 10-13 MB. DEEPENING RATES FOR THIS SURFACE LOW COULD
BRIEFLY APPROACH 1 MB PER HOUR FOR A SHORT DURATION ON MONDAY,
RESULTING IN A STRONG ISALLOBARIC RESPONSE TO THE DEEP
CYCLOGENESIS N/NW OF THE FORECAST AREA, BACKING SURFACE WINDS
ACROSS THE REGION. THIS MASS RESPONSE WILL ALSO FORM A NORTH-SOUTH
CONFLUENCE AXIS OFFSHORE FROM THE CENTRAL COAST, WHICH WILL
PROGRESS EASTWARD THROUGH THE DAY IN CONJUNCTION WITH THE
PROGRESSION OF THE EJECTING LEAD TROUGH.
EAST OF THE CONFLUENCE AXIS, A NARROW CORRIDOR OF WEAK SURFACE-
BASED BUOYANCY WILL SPREAD ACROSS THE FORECAST AREA, OWING TO THE
INFLUX OF MODEST PACIFIC MOISTURE -- LOWER TO MIDDLE 50S SURFACE
DEWPOINTS -- BEING SURMOUNTED BY RAPID MIDLEVEL COOLING AND
STEEPENING MIDLEVEL LAPSE RATES IN ADVANCE OF THE MIDLEVEL COLD
POOL CHARACTERIZED BY 500-MB TEMPERATURES AROUND -28C TO -30C
OFFSHORE. A SHALLOW, CONVECTIVE SQUALL LINE WILL FORM IN THE
VICINITY OF THE CONFLUENCE AXIS, INGESTING WEAKLY BUOYANT INFLOW
WITHIN THE LOW-BUOYANCY CORRIDOR -- SPREADING ONSHORE ALONG THE
CENTRAL COAST BY MID-DAY MONDAY AND RAPIDLY PROGRESSING EASTWARD
THROUGH THE DAY WHILE. THE TIMING OF THE SQUALL-LINE PASSAGE
THROUGH THE AREA IS EXPECTED TO BE AROUND 9AM-6PM, LIKELY CROSSING
PT. CONCEPTION BEFORE 2PM AND EXITING LOS ANGELES BY 6PM. THE
BUOYANCY, AND RESULTANT SQUALL LINE, WILL LIKELY BE TRUNCATED
NORTH OF THE TRANSVERSE RANGES, AND EAST OF THE CENTRAL COAST
RANGES, BY SIGNIFICANT BOUNDARY-LAYER THETA-E DEFICITS OWING TO
UPSLOPE PRECIPITATION AND RELATED WET-BULBING EFFECTS.
EXACT SB/MLCAPE VALUES WITHIN THE NARROW CORRIDOR OF BUOYANCY --
LIKELY IN THE 100-500 J/KG RANGE AND AIDED BY MUTED DIURNAL
DIABATIC HEATING THE MOIST AXIS -- ARE STILL UNCERTAIN, AND WILL
LIKELY REMAIN UNCERTAIN UNTIL RIGHT BEFORE THE ONSET OF THE EVENT.
HOWEVER, SEVERE-WEATHER IMPACTS WILL BE HIGHLY SENSITIVE TO THE
EXACT BUOYANCY DEVELOPING ONSHORE, TO WHICH THIS UNCERTAINTY
EXTENDS. FOR EXAMPLE, EARLY AND/OR WIDESPREAD DEVELOPMENT OF
CONVECTION NEAR OR AHEAD OF THE CONFLUENCE AXIS COULD
SIGNIFICANTLY DEPLETE BUOYANCY BY THE TIME MORE ORGANIZED
CONVECTION ARRIVES. THIS COULD GREATLY WEAKEN THE INTENSITY OF
UPDRAFTS AND DOWNDRAFTS IN THE SQUALL LINE. ALTERNATIVELY, SLOWER
EJECTION OF THE LEAD TROUGH, AND A LAGGING MIDLEVEL COLD POOL,
COULD RESULT IN WEAKER PHASING BETWEEN STEEPENING MIDLEVEL LAPSE
RATES AND ASCENT WITH THE CONFLUENCE AXIS, BOUNDARY-LAYER MOISTURE
INFLUX, AND SQUALL LINE -- RESULTING IN A CONSIDERABLY WEAKER
SQUALL-LINE VERTICAL CIRCULATION. NEVERTHELESS, THE AFOREMENTIONED
LOW-LEVEL MASS FLUXES OFFERING AMPLE CONVECTIVE MOMENTUM TRANSFER,
EVEN IN WEAK-MAGNITUDE OR WEAKLY-ORGANIZED CONVECTION, COMBINED
WITH HIGHLY FAVORABLE VERTICAL SHEAR PROFILES, WILL FAVOR THE RISK
FOR LOCALIZED DAMAGING WIND GUSTS AND PERHAPS A COUPLE OF WEAK,
BRIEF TORNADOES.
AT LEAST 35 KNOTS OF LINE-ORTHOGONAL LOW-LEVEL AND EFFECTIVE
SHEAR WILL OFFER THE POTENTIAL FOR MESOVORTICES, AND MESOCYCLONES
WITH EMBEDDED LOW-TOPPED, MINI-SUPERCELLS, TO FOCUS ISOLATED,
MESO-GAMMA-SCALE CORRIDORS OF ENHANCED WIND DAMAGE AND WEAK
TORNADOES -- WITHIN 10-20 MILES OF THE CENTRAL COAST EARLIER IN
THE DAY, AND THEN ESPECIALLY ALONG AND SOUTH OF A LINE FROM SANTA
BARBARA TO VENTURA TO OXNARD TO CAMARILLO TO MALIBU TO BEVERLY
HILLS AND HOLLYWOOD TO MONTEBELLO TO WHITTIER. LOCATIONS FARTHER
NORTH INTO THE SANTA MONICA AND SAN GABRIEL MOUNTAINS MAY
EXPERIENCE CONVECTIVELY ENHANCED WIND GUSTS TO SEVERE LEVELS, AS
CONVECTION AUGMENTS THE BACKGROUND STRONG GRADIENT WINDS, EVEN
WHERE SNOW IS OCCURRING AT ELEVATIONS ABOVE 6-6.5 KFT. LOCAL
CONVECTIVELY-ENHANCED GUSTS COULD EVEN BRIEFLY EXCEED 70 MPH IN
THESE AREAS, THOUGH THE TORNADO RISK WILL BE CONFINED TO AREAS
FARTHER SOUTH WHERE SURFACE DEWPOINTS EXCEED AROUND 50F MODESTLY
BOOSTING LOW-LEVEL BUOYANCY.
AS ADDRESSED ABOVE, REGARDING ALTERNATE SCENARIOS, LESSER
COVERAGE OF SHOWERS AHEAD OF THE SQUALL LINE AND GREATER SYNOPTIC-
SCALE PHASING OF THE MIDLEVEL COLD POOL AND LOW-LEVEL MOIST AXIS
WOULD BOOST BUOYANCY AND THE RISK FOR SEVERE WIND GUSTS AND
TORNADOES. MEANWHILE, GREATER PRE-SQUALL LINE SHOWER COVERAGE IN
THE WARM-ADVECTION WING OF THE SYNOPTIC SYSTEM, AND LESS
FAVORABLE UPPER-LEVEL PHASING, COULD GREATLY LIMIT THE SEVERE-
WEATHER RISK. IMPACTS WITHIN THE VERY-LOW-CAPE PART OF THE
THERMODYNAMIC PARAMETER SPACE ARE HIGHLY SENSITIVE TO SMALL
VARIATIONS IN BUOYANCY GIVEN THE NON-LINEAR FEEDBACKS IN STRONGLY
SHEARED ENVIRONMENTS, AND THE COVERAGE/INTENSITY OF SEVERE-
WEATHER HAZARDS MAY NOT BECOME CLEAR UNTIL THE WEATHER EVENT IS
UNFOLDING. THIS IS A MAJOR FACTOR, COMBINED WITH THE ELEVATED
CONDITIONAL RISK FOR SEVERE STORMS, FOR INTERESTS TO REMAIN AT A
HIGH STATE OF WEATHER READINESS ON MONDAY. REGARDING PREPAREDNESS,
IF WINDS GREATLY INTENSIFY, REMAINING INDOORS IN THE LOWEST PART
OF A BUILDING AND AWAY FROM WINDOWS WOULD GREATLY HELP MITIGATE
IMPACTS FROM SUCH SEVERE-WEATHER HAZARDS.
BY 6PM MONDAY, THE SQUALL LINE WILL LIKELY HAVE PUSHED EAST AND
SOUTH OF THE FORECAST AREA. HOWEVER, THROUGH THE DAY MONDAY AND
CONTINUING INTO MONDAY NIGHT, SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS WILL CONTINUOUSLY RE-GENERATE BEHIND THE SQUALL
LINE ACROSS MUCH OF THE REGION. THIS WILL OCCUR AS THE COLD POOL
ALOFT CONTINUES TO OVERSPREAD THE AREA AND WEAK-VORTICITY CENTERS
MOVE ACROSS THE AREA, AND FRICTIONAL CONVERGENCE NEAR THE COAST,
TERRAIN-CIRCULATIONS, AND RESIDUAL CONVECTIVE BOUNDARIES
FOCUS SUBSEQUENT CONVECTIVE DEVELOPMENT AMID THE STEEPENING
MIDLEVEL LAPSE RATES, WHICH WILL OFFSET THE DECREASING POST-
SQUALL-LINE MOISTURE. WHILE THE COVERAGE OF THIS ACTIVITY WILL BE
LESSER, UPDRAFTS WILL HAVE A TENDENCY TO EXTEND DEEPER INTO ICING
LAYERS ALOFT OWING TO THE MIDLEVEL COOLING, AND LIGHTING STRIKES
WOULD BE MORE LIKELY WITH THIS ACTIVITY, COMPARED TO THE SQUALL
LINE THAT COULD CONTAIN NO LIGHTNING. SURFACE WINDS WILL VEER IN
THE WAKE OF THE SQUALL LINE, SO HODOGRAPHS WILL BE LESS FAVORABLE
FOR LOW-LEVEL MESOCYCLONES TO RAPIDLY FORM, HOWEVER THE AMPLE
BACKGROUND VERTICAL VORTICITY AND CONTINUED INTENSE MOMENTUM
FIELDS ALOFT WOULD SUPPORT BOTH WEAK NON-SUPERCELL TORNADO AND
STRONG TO LOCALLY DAMAGING CONVECTIVE WIND-GUST POTENTIAL, AS
WELL AS THE RISK FOR SMALL HAIL, BEHIND THE SQUALL LINE INTO
MONDAY NIGHT. SUCH RISK WOULD BE MAXIMIZED BEFORE SUNSET WHEN LOW-
LEVEL LAPSE RATES ARE DIURNALLY STEEPER.
*BURN-SCAR DEBRIS FLOWS, FLASH FLOODING, AND ROCK AND MUD SLIDES:
PRECIPITATION RATES WITH THE AFOREMENTIONED SQUALL LINE WILL
LIKELY REACH 0.75-1 INCH PER HOUR IN MANY AREAS, WITH MUCH OF THAT
RAIN FALLING IN 15-30 MINUTES. AS A RESULT, THERE IS AN INCREASING
CHANCE (AT LEAST 50%) FOR BURN-SCAR DEBRIS THRESHOLDS TO BE AT
LEAST MARGINALLY EXCEEDED FOR THE BURN SCARS. THESE RAINFALL RATES
MAY SUPPORT AT LEAST MINOR DEBRIS FLOWS ON THE BURN SCARS, AND
THERE IS A REMOTE POSSIBILITY (20% CHANCE) FOR A MORE SIGNIFICANT,
DAMAGING BURN-SCAR DEBRIS FLOW TO DEVELOP IN LOS ANGELES COUNTY
WHERE MOISTURE FLUXES AHEAD OF THE SQUALL LINE MAXIMIZE WITH
MUTED DAYTIME HEATING. OUTSIDE OF THE BURN SCARS, SUCH RAINFALL
RATES WILL BE CONDUCIVE FOR FLASH FLOODING IN AND AROUND ROADWAYS,
AND SMALLER CREEKS AND STREAMS -- POTENTIALLY BECOMING
SIGNIFICANT IN AND AROUND LA. IN AND AROUND THE MOUNTAINS AND
FOOTHILLS, ESPECIALLY IN LA AND VENTURA COUNTIES, THE PREVIOUSLY
MENTIONED INTENSE LOW-LEVEL JET WILL PROLONG THE DURATION OF MORE
EXTREME RAINFALL RATES BY AUGMENTING ASCENT THROUGH STRONG UPSLOPE
FLOW AMID 1+ INCH PRECIPITABLE WATER. IN THESE AREAS, MORE
SIGNIFICANT FLASH FLOODING, ALONG WITH DANGEROUS ROCK AND MUD
SLIDES, WILL BE POSSIBLE, AND THESE CONDITIONS COULD REACH LIFE-
THREATENING MAGNITUDES ON A LOCALIZED BASIS -- THOUGH EVENT,
TIMING, AND LOCATION UNCERTAINTY FOR SUCH CONDITIONS IS CURRENTLY
SIGNIFICANT. FLOOD WATCHES HAVE BEEN ISSUED 9AM-9PM MONDAY ALONG
AND SOUTH OF THE TRANSVERSE RANGES TO ADDRESS THE INCREASING RISK
FOR DANGEROUS FLOODING TO DEVELOP ON MONDAY. WHILE FLOODING
POTENTIAL WILL SLOWLY DECREASE FOLLOWING THE PASSAGE OF THE SQUALL
LINE, MORE CELLULAR CONVECTION IN ITS WAKE WILL LOCALLY PROLONG
FLOODING POTENTIAL ON A LOCALIZED BASIS, GIVEN THE SATURATED
ANTECEDENT GROUND.
ALSO OF NOTE, WITH SNOW LEVELS EXPECTED TO REMAIN IN THE 6-6.5 KFT
RANGE DURING THE DURATION OF MOST INTENSE RAINFALL RATES. ABOVE
THESE ELEVATIONS, HEAVY-SNOW ACCUMULATIONS WILL LOCALLY MITIGATE
THE BURN-SCAR DEBRIS-FLOW POTENTIAL. THUS, THE BURN-SCAR DEBRIS
POTENTIAL WILL BE ELEVATION-DEPENDENT, AND WILL SHOULD QUICKLY
WHERE THERE IS AN ONSET OF HIGH-ELEVATION SNOW.
*HEAVY MOUNTAIN SNOW:
WITH THE ONSET OF INTENSE PRECIPITATION RATES PREVIOUSLY MENTIONED,
AND SNOW LEVELS HOLDING AROUND 6-6.5 KFT ON MONDAY, THE ONSET OF
AN EXTENDED DURATION OF HEAVY MOUNTAIN SNOW WILL ACCOMPANY THE
NORTH EDGE OF THE SQUALL LINE AND PERIPHERAL UPSLOPE-FLOW-ENHANCED
PRECIPITATION OVER THE TRANSVERSE RANGES ON MONDAY. WHILE THE
COVERAGE OF AFFECTED AREA WILL BE LIMITED BY THE WARM-ADVECTION-
BOOSTED SNOW LEVELS, AT LEAST SEVERAL INCHES OF SNOW COULD
ACCUMULATE ABOVE 6 KFT IN THE EASTERN SAN GABRIEL AND THE NORTHERN
VENTURA COUNTY MOUNTAINS BY LATE MONDAY AFTERNOON. AND THEN
THROUGH MONDAY NIGHT, AS COOLING ALOFT FURTHER OVERTAKES THE LOCAL
AREA, SNOW LEVELS WILL FALL TO AROUND 4-4.5 KFT WHILE
PRECIPITATION REGENERATES (ALBEIT NOT AS HEAVY) -- BRINGING A
LARGER AREAL COVERAGE OF MOUNTAIN SNOWS ACROSS THE HIGHER
ELEVATIONS IN LA AND VENTURA COUNTIES. SNOW WILL BEGIN TAPERING
OFF BY LATE MONDAY NIGHT, BUT NOT BEFORE 1 TO 2 FEET OF SNOW
ACCUMULATE ABOVE 6 KFT, WITH 3-6 INCHES OF SNOW ACCUMULATING IN
MANY AREAS FROM 4 TO 6 KFT. AND WITH THE SNOW COMBINING WITH THE
PREVIOUSLY MENTIONED LOW-LEVEL JET INTERCEPTING THE HIGH TERRAIN
TO BRING 60-70 MPH WIND GUSTS PRODUCING BLOWING/DRIFTING SNOW AND
REDUCED VISIBILITIES, A WINTER STORM WATCH HAS BEEN POSTED FOR THE
EASTERN SAN GABRIELS AND NORTHERN VENTURA COUNTY MOUNTAINS
STARTING AT 6AM MONDAY. EVEN AFTER SNOW TEMPORARILY ENDS BY EARLY
TUESDAY MORNING, BLOWING AND DRIFTING SNOW AND REDUCED
VISIBILITIES WILL BE A CONCERN, ALONG WITH ROADWAYS REMAINING SNOW
COVERED, AND THE WINTER STORM WATCH WILL CONTINUE THROUGH
THURSDAY MORNING.
*STRONG TO DAMAGING GRADIENT WINDS:
AS ADDRESSED ABOVE, THERE WILL BE A SIGNIFICANT LOW-LEVEL JET
CROSSING THE REGION IN CONJUNCTION WITH THE EJECTING MIDLEVEL
SHORTWAVE TROUGH. AS THE LOW-LEVEL JET INTERCEPTS THE INTERIOR
MOUNTAINS -- ESPECIALLY THOSE ORIENTED WEST-TO-EAST, GUSTS OF
60-70 MPH ARE ANTICIPATED TO DEVELOP INCLUDING THROUGH PASSES AND
CANYONS. WHILE CONVECTION AND THE DEVELOPMENT OF GRAVITY WAVES
COULD ENHANCE THESE WINDS EVEN FURTHER, THE POTENTIAL FOR SEVERAL
HOURS OF GUSTS EXCEEDING 60 MPH WARRANT THE ISSUANCE OF HIGH WIND
WATCHES FOR THE WESTERN SAN GABRIELS, I-5 CORRIDOR OF NW LA
COUNTY, THE ANTELOPE VALLEY FOOTHILLS, SOUTHERN VENTURA COUNTY
MOUNTAINS, AND THE SANTA BARBARA COUNTY INTERIOR MOUNTAINS.
THESEUPCOMING STORMAREAS ARE OUTSIDE OF WINTER STORM WATCHES,
AND ALTHOUGH ANY SNOW IN MOUNTAINOUS LOCATIONS IN THESE AREAS
SHOULD BE LIMITED IN COVERAGE AND MAGNITUDE GIVEN COMPARATIVELY
HIGH SNOW LEVELS, ISOLATED SPOTS OF HIGH-ELEVATION SNOW AND
BLOWING/DRIFTING SNOW REDUCING VISIBILITIES WILL BE POSSIBLE IN
THE HIGH WIND WARNING AREAS.
OUTSIDE OF THE HIGH WIND WARNING AREAS, WIDESPREAD 35-50 MPH
SOUTHERLY WIND GUSTS ARE ANTICIPATED FOR SEVERAL HOURS --
PROVIDED MECHANICAL AND BUOYANT MIXING INTO THE DEEP LAYER OF THE
SIGNIFICANT MASS RESPONSE, CHARACTERIZED BY 30-40 KT MEAN WINDS IN
THE 0-1-KM AND 0-3-KM LAYERS, AND THE TIGHTENING SURFACE PRESSURE
GRADIENT AND ISALLOBARIC FLOW RESPONSE TO THE DEEPENING SURFACE
CYCLONE. A WIND ADVISORY HAS BEEN POSTED FOR THE REMAINDER OF THE
FORECAST AREA FOR MONDAY. IF POCKETS OF SEVERE CONVECTIVE WINDS
WERE TO BECOME IMMINENT ON MONDAY, ESPECIALLY IN THE WIND ADVISORY
AREA, THEN SHORTER-FUSE CONVECTIVE WARNINGS COULD BECOME
REQUIRED.
WIND ADVISORIES AND HIGH WIND WARNINGS WILL BE IN EFFECT 6AM TO
6PM MONDAY. THIS WOULD BE IN CONJUNCTION WITH THE STRONGEST LOW-
LEVEL MASS RESPONSE, AND AHEAD OF THE EXPANDING MIDLEVEL COLD
CORE THAT WILL PROLONG CONVECTIVE/FLOODING POTENTIAL BEYOND
CESSATION OF STRONGER GRADIENT WINDS.
*HIGH SURF AND COASTAL FLOODING:
HIGH SURF ADVISORIES HAVE BEEN POSTED, AND ISOLATED MINOR COASTAL
FLOODING WILL BE POSSIBLE IN LOCATIONS MOST VULNERABLE TO
SIGNIFICANT NORTHWEST SWELL. PLEASE REFERENCE THE BEACHES SECTION
BELOW FOR MORE INFORMATION.
LONG TERM (WED-SAT)
14/202 PM.
LOOKING FURTHER AHEAD, THE LARGE, UPPER-LEVEL LONGWAVE TROUGH
WILL REMAIN ANCHORED ACROSS THE WESTERN CONUS THROUGHOUT MUCH OF
THE REMAINDER OF THE UPCOMING WEEK. THIS WILL BE REINFORCED BY
MULTIPLE IMPULSES OF COMPACT VORTICITY AND ACCOMPANYING SPEED
MAXIMA PIVOTING THROUGH THE WESTERN RIM OF THE LARGER-SCALE
TROUGHING. IT APPEARS THAT SOUTHERN CALIFORNIA WILL BE BENEATH
THE TRAJECTORY OF MULTIPLE IMPULSES THROUGH THE REMAINDER OF THE
UPCOMING WEEK. EACH IMPULSE WILL HAVE THE POTENTIAL TO BOOST
PRECIPITATION RATES AND WINDS WITHIN A RATHER LONG DURATION OF ON-
AND-OFF SHOWERS, COLD, AND BLUSTERY CONDITIONS. THE PROGRESSIVE
NATURE OF EACH IMPULSE FOLLOWING THE MONDAY, MORE-FAVORABLE-FOR-
FLOODING EVENT MAY TEND TO MITIGATE SUBSEQUENT FLOODING IMPACTS.
HOWEVER, INCREASINGLY SATURATED GROUND CONDITIONS COULD OFFSET THE
SHORT-DURATION PRECIPITATION CHARACTER TO MAINTAIN, OR EVEN
BOOST, FLOODING CONCERNS THROUGH THE WEEK, AND UNCERTAINTY
REGARDING HYDROLOGICAL IMPACTS GROWS QUICKLY THROUGH THE COURSE OF
THE WEEK. REGARDLESS, TEMPERATURES THROUGH THE WEEK IN MOST AREAS
WILL BE QUITE COOL, IN THE 50S AND LOWER 60S AS HIGH
TEMPERATURES, WHILE SNOW LEVELS GRADUALLY FALL IN RESPONSE TO COLD
ADVECTION WITH EACH PASSING IMPULSE. COLD-WEATHER IMPACTS COULD
BECOME OF INCREASING CONCERN THROUGH THE WEEK.
THE UPCOMING TUESDAY NIGHT THROUGH WEDNESDAY SYSTEM IS A MORE-
LIKELY PERIOD OF STRONGER JET ENERGY PASSING OVER THE LOCAL AREA,
PROVIDING MORE PRECIPITATION AND GUSTY WINDS. IN ADDITION TO THE
RISK FOR AT LEAST MINOR FLOODING, COOLING ALOFT AND LOWERING SNOW
LEVELS WILL BRING ANOTHER ROUND OF HEAVY SNOW IN THE MOUNTAINS BUT
OVER A BROADER AREA GIVEN LOWERING SNOW LEVELS. HEAVY SNOW, WITH
BLOWING AND DRIFTING SNOW, COULD IMPACT ELEVATIONS AS LOW AS 3000
OR 4000 FT ELEVATION INCLUDING THE GRAPEVINE OF THE INTERSTATE-5
CORRIDOR, IF ENHANCED MOSITURE CAN ADEQUATELY PHASE WITH COOLING
ALOFT. THIS WILL DEPEND ON NUMEROUS MESOSCALE FACTORS FOR WHICH
UNCERTAINTY IS SIGNIFICANT. THE WINTER STORM WATCH EXPANDS
STARTING TUESDAY NIGHT TO INCLUDE SANTA BARBARA COUNTY INTERIOR
MOUNTAINS, SOUTHERN VENTURA COUNTY MOUNTAINS, AND THE INTERSTATE 5
CORRIDOR, REMAINING IN EFFECT FOR THE EASTERN SAN GABRIEL AND
NORTHERN VENTURA COUNTY MOUNTAINS. BEFORE THE SYSTEM DEPARTS,
ACROSS THE WINTER STORM WATCH AREAS, TOTAL SNOW ACCUMULATIONS
COULD REACH 1 TO 4 INCHES FOR 3500 TO 4500 FEET ELEVATION
POSSIBLE, 6 TO 12 INCHES FOR 4500 TO 6000 FEET ELEVATION POSSIBLE,
AND ONE TO TWO FEET ABOVE 6000 FEET ELEVATION POSSIBLE. WINTER
STORM WATCHES CONTINUE THROUGH THURSDAY MORNING, WHEN THE SNOW
TAPERS OFF.
WHILE A DRYING TREND MAY OCCUR ON FRIDAY AND SATURDAY, THE
POTENTIAL FOR PRECIPITATION CANNOT BE RULED OUT THROUGH LATE IN
THE UPCOMING WEEK AND INTO NEXT WEEKEND, AS EMBEDDED IMPULSES
TRACK ACROSS THE LOCAL AREA.
AVIATION
15/0653Z.
AT 0450Z AT KLAX, THERE WAS NO MARINE LAYER AND NO INVERSION.
HIGH CONFIDENCE IN TAFS FOR KPMD AND KWJF.
LOW TO MODERATE CONFIDENCE IN THE REMAINDER OF THE TAFS. 1 TO 3
HOUR PERIODS OF MVFR CIGS ARE POSSIBLE AT ANY TIME.
KLAX...MODERATE CONFIDENCE IN TAF. 1 TO 3 HOUR PERIODS OF
BKN020-025 CIGS ARE POSSIBLE AT ANYTIME. THERE IS A 25 PERCENT
CHC OF A 8KT EAST WIND COMPONENT 10Z-16Z. A STRONG STORM MONDAY
WILL BRING STRONG EAST WINDS, RAIN AND A SLIGHT CHC OF TSTMS.
KBUR...MODERATE CONFIDENCE IN TAF. 1 TO 3 HOUR PERIODS OF
BKN020-025 CIGS ARE POSSIBLE AT ANYTIME.
MARINE
14/759 PM.
FOR THE OUTER WATERS, MODERATE TO HIGH CONFIDENCE IN CURRENT
FORECAST. TONIGHT AND SUNDAY, SOUTHEAST WINDS WILL INCREASE TO
SCA LEVELS AS WELL AS THE SEAS. FOR SUNDAY NIGHT THROUGH
WEDNESDAY, HIGH CONFIDENCE IN SCA LEVEL WINDS AND SEAS, WITH A
50-70% CHANCE OF GALE FORCE WINDS SUNDAY EVENING THROUGH MONDAY
NIGHT, EXCEPT THROUGH TUESDAY AFTERNOON FOR THE WATERS FROM 0 TO
60 NM OFFSHORE ALONG THE CENTRAL COAST (PZZ645 AND PZZ670).
FOR THE INNER WATERS NORTH OF POINT SAL, MODERATE TO HIGH
CONFIDENCE IN CURRENT FORECAST. THROUGH TONIGHT, HIGH CONFIDENCE
IN WINDS AND SEAS REMAINING BELOW SCA LEVELS, EXCEPT FOR LOCALLY
IN THE FAR WESTERN PORTION. FOR SUNDAY THROUGH WEDNESDAY, HIGH
CONFIDENCE IN COMBINATION OF SCA LEVEL WINDS AND SEAS DEVELOPING.
THERE IS ALSO A 50-60% CHANCE OF GALE FORCE WINDS SUNDAY EVENING
THROUGH TUESDAY AFTERNOON.
FOR THE INNER WATERS SOUTH OF POINT CONCEPTION, MODERATE TO HIGH
CONFIDENCE IN CURRENT FORECAST WITH WINDS AND SEAS REMAINING
BELOW SCA LEVELS THROUGH SUNDAY AFTERNOON. FOR SUNDAY EVENING
THROUGH WEDNESDAY, SCA LEVEL WINDS ARE LIKELY AND THERE IS A
40-50% CHANCE OF GALE FORCE WINDS ON MONDAY.
A SQUALL LINE WILL LIKELY DEVELOP IN ASSOCIATION WITH THE COLD
FRONT LATE SUNDAY NIGHT THROUGH MONDAY, WHICH WILL RESULT IN
HAZARDOUS MARINE CONDITIONS. THESE INCLUDE: GALE FORCE WINDS,
DANGEROUS LIGHTNING, HEAVY RAINFALL WITH REDUCED VISIBILITY, AND
WATERSPOUTS.
BEACHES
14/753 PM.
A HIGH SURF ADVISORY FOR THE CENTRAL COAST WILL EXPIRE AT 900 PM
THIS EVENING AS THE SWELL DECREASES.
A PERIOD OF VERY LARGE WAVES IS EXPECTED TO START ON MONDAY, WITH
SURF GENERALLY PEAKING TUESDAY AND WEDNESDAY ACROSS WEST FACING
BEACHES. HIGH SURF ADVISORIES AND BEACH HAZARD STATEMENTS ARE IN
EFFECT FOR ALL COASTS, SEE THE CFWLOX AND SRFLOX PRODUCTS FOR MORE
DETAILS.
ELEVATED HIGH TIDES AS THE NEW MOON CYCLE APPROACHES WILL COINCIDE
WITH THE ARRIVAL OF THE HIGHER SURF AND SWELL. THIS WILL BRING AN
ELEVATED CHANCE OF COASTAL FLOODING, OR AT THE VERY LEAST, MINOR
TIDAL OVERFLOWS ESPECIALLY DURING THE TIME OF THE HIGH TIDES,
PARTICULARLY ON TUESDAY AND WEDNESDAY. A COASTAL FLOOD ADVISORY
MAY BE NEEDED SHOULD SWELL GUIDANCE REMAIN CONSISTENT ALONG WITH
WIND- DRIVEN FACTORS.
LOX WATCHES/WARNINGS/ADVISORIES
CA...HIGH WIND WATCH IN EFFECT FROM MONDAY MORNING THROUGH MONDAY
AFTERNOON FOR ZONES 38-344-345-353-376-378-379-381-382. (SEE LAXNPWLOX).
WIND ADVISORY IN EFFECT FROM 6 AM TO 6 PM PST MONDAY FOR
ZONES 87-88-340>343-346>352-354>358-366>375-383-548. (SEE LAXNPWLOX).
FLOOD WATCH IN EFFECT FROM MONDAY MORNING THROUGH MONDAY
EVENING FOR ZONES 87-88-348>358-362-366>380-548>550. (SEE LAXFFALOX).
HIGH SURF ADVISORY IN EFFECT FROM 10 AM MONDAY TO 6 PM PST
THURSDAY FOR ZONES 340-346-362-366. (SEE LAXCFWLOX).
BEACH HAZARDS STATEMENT IN EFFECT FROM MONDAY MORNING THROUGH
WEDNESDAY MORNING FOR ZONES 349-350. (SEE LAXCFWLOX).
WINTER STORM WATCH REMAINS IN EFFECT FROM TUESDAY EVENING
THROUGH THURSDAY MORNING FOR ZONES 353-376-378. (SEE LAXWSWLOX).
HIGH SURF ADVISORY IN EFFECT FROM 10 AM MONDAY TO NOON PST
THURSDAY FOR ZONE 354. (SEE LAXCFWLOX).
WINTER STORM WATCH REMAINS IN EFFECT FROM MONDAY MORNING
THROUGH THURSDAY MORNING FOR ZONES 377-380. (SEE LAXWSWLOX).
PZ...GALE WATCH IN EFFECT FROM SUNDAY EVENING THROUGH TUESDAY
AFTERNOON FOR ZONES 645-670. (SEE LAXMWWLOX).
GALE WATCH IN EFFECT FROM SUNDAY EVENING THROUGH MONDAY
AFTERNOON FOR ZONE 650. (SEE LAXMWWLOX).
GALE WATCH IN EFFECT FROM LATE SUNDAY NIGHT THROUGH MONDAY
AFTERNOON FOR ZONE 655. (SEE LAXMWWLOX).
GALE WATCH IN EFFECT FROM SUNDAY EVENING THROUGH LATE MONDAY
NIGHT FOR ZONES 673-676. (SEE LAXMWWLOX).
PUBLIC...MUNROE/COHEN
AVIATION...RORKE
MARINE...BLACK/RAT/RS/CC
BEACHES...BLACK/CILIBERTI/RS
SYNOPSIS...COHEN/CILIBERTI
WEATHER.GOV/LOSANGELES
EXPERIMENTAL GRAPHICAL HAZARDOUS WEATHER OUTLOOK AT:
HTTPS://WWW.WEATHER.GOV/ERH/GHWO?WFO=LOX
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