608  
FXUS66 KLOX 181740  
AFDLOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA  
940 AM PST WED JAN 18 2017  
   
SYNOPSIS
 
 
SEVERAL STORMS WILL BRING PRECIPITATION AND GUSTY WINDS THROUGH  
EARLY NEXT WEEK. THERE MAY BE A CHANCE OF THUNDERSTORMS ON THURSDAY  
AND FRIDAY. THE FIRST STORM WILL ARRIVE ON WEDNESDAY AND THURSDAY.  
THE SECOND...FROM LATE THURSDAY INTO EARLY SATURDAY AND WILL HAVE  
HEAVY RAIN ESPECIALLY IN THE FOOTHILLS...AND LOWER SNOW LEVELS.  
THE THIRD...WILL BE ON SUNDAY INTO MONDAY WITH THE HIGHEST  
PRECIPITATION AMOUNTS. THE TEMPERATURES WILL BE BELOW NORMAL INTO  
NEXT WEEK.  
 

 
   
SHORT TERM
 
(TDY-FRI)  
 
THE FIRST OF A SERIES OF STORMS WILL BE ARRIVING TODAY AND  
TONIGHT. ALREADY SEEING SOME SHOWERS DEVELOPING NORTH OF PT  
CONCEPTION THIS MORNING WELL AHEAD OF THE MAIN ACTIVITY WHICH IS  
STILL OVER THE BAY AREA. THIS MORNING'S PRECIP WON'T AMOUNT TO  
MORE THAN A FEW SPRINKLES OR LIGHT SHOWERS BUT IT WAS A LITTLE  
MORE THAN WHAT WE HAD EXPECTED SO THE FORECAST HAS BEEN UPDATED TO  
INCLUDE SOME SCATTERED SHOWERS THERE AT LEAST THROUGH THE MORNING.  
AND THE FASTER SPEED SHOULD ALSO ALLOW THE MAIN ACTIVITY OVER THE  
BAY AREA TO ARRIVE A LITTLE FASTER AS WELL SO THE AFTERNOON POPS  
WERE INCREASED ACROSS NORTHERN SLO COUNTY. EVERYTHING ELSE IN THE  
SHORT TERM LOOKS GOOD.  
 
***FROM PREVIOUS DISCUSSION***  
 
THE TROUGH WILL SHARPEN UP AND TAKE ON A SLIGHT NEGATIVE TILT AS  
IT MOVES ACROSS THE REGION TONIGHT AND THU MORNING. THIS SHOULD  
HELP TO MAINTAIN OR EVEN ENERGIZE THE SURFACE FRONT AS IT PUSHES  
ACROSS THE FORECAST AREA TONIGHT. RAIN WITH THE MAIN FRONT WILL  
OVERSPREAD SLO AND SBA COUNTIES THIS EVENING, THEN REACH LOS  
ANGELES COUNTY BY LATE TONIGHT. EXPECT A 3 TO 5 HOUR PERIOD OF  
STEADY MODERATE TO OCCASIONALLY HEAVY RAIN AS THE FRONT PUSHES  
ACROSS THE REGION. INCREASING UPPER LEVEL DIFFLUENCE AND COOLING  
ALOFT WILL HELP TO DESTABILIZE THE ATMOSPHERE SUFFICIENTLY TO  
ALLOW FOR A SLIGHT CHANCE OF THUNDERSTORMS WITH THE FRONT. RAIN  
WILL TURN TO SHOWERS ACROSS SLO AND SBA COUNTIES LATE TONIGHT, AND  
BY MID MORNING THURSDAY ACROSS THE L.A. BASIN. THERE WILL BE  
PLENTY OF LOW LEVEL MOISTURE AND CYCLONIC FLOW, SO THERE WILL BE A  
THREAT OF LINGERING SHOWERS INTO THE EVENING HOURS, ESPECIALLY IN  
THE MOUNTAINS.  
 
RAINFALL INTENSITIES WITH THE FRONT SHOULD BE ON THE ORDER OF ONE  
QUARTER TO ONE HALF INCH PER HOUR, POSSIBLY BRIEFLY HIGHER IN ANY  
THUNDERSTORMS. THIS COULD BE INTENSE ENOUGH TO GENERATE SOME MINOR  
MUD AND DEBRIS FLOWS IN AND AROUND THE RECENT BURN AREAS. THERE  
WILL BE A PERIOD OF GUSTY SOUTH WINDS AHEAD OF AND NEAR THE FRONT,  
ESPECIALLY ACROSS SLO AND SBA COUNTIES, WHERE WINDS COULD REACH  
LOW END ADVISORY LEVELS. THE SOUTH FLOW WILL ALSO HELP TO PRODUCE  
SOME ENHANCEMENT OF THE RAIN ON AND BELOW SOUTH AND SOUTHWEST  
SLOPES IN THE MTNS AND FOOTHILLS.  
 
EXPECT WIDESPREAD RAINFALL TOTALS OF 0.75 TO 1.25 INCHES ACROSS  
THE FORECAST AREA, WITH LOCAL TOTALS OF 1.5 TO 2 INCHES POSSIBLE  
IN FAVORED TERRAIN. SNOW LEVELS WILL LOWER TO 5000 TO 5500 FEET  
LATE TONIGHT AND THU MORNING, AND SNOW ACCUMULATIONS OF 5 TO 10  
INCHES ARE EXPECTED, MAINLY ABOVE 6500 FEET. WINTER WEATHER  
ADVISORIES ARE IN EFFECT LATE THIS EVENING THROUGH THU EVENING  
FOR THE MTNS OF L.A. AND VTU COUNTIES, THOUGH MOST OF THE  
ACCUMULATING SNOW SHOULD BE OVER BY AFTERNOON.  
 
THERE WILL BE SOMEWHAT OF A BREAK IN THE RAIN THU NIGHT, THEN A  
VERY STRONG AND COLD UPPER LOW FROM THE SOUTHERN GULF OF ALASKA  
WILL APPROACH THE OREGON COAST BY EARLY FRI MORNING, POWERED BY  
A 175 KT WEST-NORTHWEST JET AIMED RIGHT AT THE FORECAST AREA.  
A NICELY DIFFLUENT HEIGHT PATTERN WILL SET UP ACROSS THE REGION  
EARLY FRI MORNING. EXPECT STEADY RAIN TO DEVELOP ON THE CENTRAL  
COAST LATE THU NIGHT, THEN RAPIDLY OVERSPREAD THE REGION EARLY  
FRI MORNING. RAIN WILL BE HEAVIEST ON THE CENTRAL COAST JUST  
BEFORE DAYBREAK, WITH THE HEAVIEST RAIN SHIFTING INTO THE L.A.  
BASIN DURING THE MID MORNING HOURS AND CONTINUING INTO THE  
AFTERNOON. RAIN WILL TURN TO SHOWERS IN THE AFTERNOON, BUT  
NUMEROUS SHOWERS SHOULD LINGER INTO FRI NIGHT. THIS SYSTEM WILL  
BE VERY DYNAMIC AND COLD, SO HAVE ADDED A SLIGHT CHANCE OF TSTMS  
ACROSS THE REGION ON FRI. THE LIMITING FACTOR FOR RAINFALL TOTALS  
WILL AGAIN BE THE SPEED OF THE SYSTEM WITH THE JET PUNCHING IT  
THROUGH QUICKLY. STILL 1 TO 2 INCHES OF RAIN ARE LIKELY IN MANY  
AREAS WITH LOCALLY HIGHER TOTALS IN THE FOOTHILLS. SNOW LEVELS  
WILL BE LOWER, POSSIBLY DOWN TO 4000 TO 4500 FEET BY FRI NIGHT.  
SIGNIFICANT SNOWFALL IS EXPECTED IN THE MOUNTAINS, AND WINDS WILL  
BE QUITE STRONG, SO WINTER STORM WATCHES WILL LIKELY HAVE TO BE  
ISSUED FOR FRI INTO FRI NIGHT.  
   
LONG TERM
 
(SAT-TUE)  
 
A VERY WEAK FLAT RIDGE MAY BRING SOME RESPITE FROM THE RAIN SATURDAY  
INTO SATURDAY NIGHT, BUT THERE STILL WILL BE PLENTY OF LOW LEVEL  
MOISTURE, SO THERE WILL LIKELY BE LOTS OF CLOUDINESS AND A CHANCE  
OF SHOWERS FROM TIME TO TIME JUST ABOUT ANYWHERE.  
 
A STRONG UPPER LOW MOVING THROUGH THE EASTERN PACIFIC WILL TAKE  
ON A NEGATIVE TILT AS IT APPROACHES THE WEST COAST LATE SAT AND  
SAT NIGHT. THIS HAS THE POTENTIAL TO BRING THE MOST PRECIPITATION  
OF ALL THREE SYSTEMS TO MUCH OF THE REGION FOR A FEW REASONS. IT  
WILL TAP INTO AN AREA OF SOMEWHAT HIGHER PW VALUES...THE  
SOUTHWESTERLY JET STREAM WILL BE PARALLEL TO THE SURFACE FRONT FOR  
A TIME, RESULTING IN SLOWER MOVEMENT OF THE FRONT AND A LONGER  
DURATION OF RAIN...AND THERE WILL BE A LONGER PERIOD OF STRONG  
SOUTHERLY LOW LEVEL FLOW.  
 
THERE ARE STILL SOME TIMING DIFFERENCES BETWEEN THE MODELS, BUT  
IT LOOKS AS THOUGH THE PERIOD OF HEAVIEST RAIN FOR SLO AND SBA  
COUNTIES WILL BE FROM SUNDAY MORNING INTO MID SUNDAY AFTERNOON,  
FOR VENTURA COUNTY FROM EARLY SUNDAY AFTERNOON THROUGH LATE SUNDAY  
EVENING, AND FOR LOS ANGELES COUNTY FROM LATE SUNDAY AFTERNOON  
THROUGH LATE SUNDAY NIGHT. LOTS OF MOISTURE AND ANOTHER WEAK  
IMPULSE WILL KEEP QUITE A BIT OF SHOWER ACTIVITY BEHIND THE FRONT  
THROUGH MONDAY AFTERNOON. THIS WILL BE A WARMER SYSTEM, AT LEAST  
INITIALLY, BUT SNOW LEVELS WILL LOWER SHARPLY SUNDAY NIGHT AND  
NORTH SLOPE SNOW COULD AFFECT TRAVEL ON INTERSTATE 5 THROUGH THE  
GRAPEVINE LATE SUNDAY NIGHT INTO MONDAY EVENING. RAINFALL TOTALS  
WITH THIS LAST SYSTEM COULD AVERAGE 1.5 TO 3 INCHES ACROSS THE  
REGION, WITH HIGHER TOTALS ON AND BELOW SOUTH AND SOUTHWEST FACING  
FOOTHILLS, AND 0.50 TO 1 INCH IN THE ANTELOPE VALLEY.  
 
SIGNIFICANT SNOW WILL FALL IN THE MOUNTAINS ABOVE 6500 OR 7000  
FEET, WITH SNOW ACCUMULATIONS POSSIBLY DOWN TO 3500 TO 4000 FEET  
TOWARD THE END OF THE EVENT. DRY WEATHER IS EXPECTED FOR TUE,  
ALTHOUGH IT WILL REMAIN QUITE CHILLY.  
 

 
   
AVIATION
 
18/1215Z.  
 
AT 11Z, THE MARINE LAYER DEPTH WAS AROUND 1300 FEET DEEP AT KLAX.  
THE TOP OF THE INVERSION WAS NEAR 1600 FEET WITH A TEMPERATURE  
AROUND 13 DEGREE CELSIUS.  
 
N OF POINT CONCEPTION...MODERATE CONFIDENCE THROUGH 20Z...AFTER  
THAT LOW CONFIDENCE AS LIGHT RAIN OR DRIZZLE WILL CAUSE VSBYS TO  
LOWER TO MVFR CIGS. 40% CHANCE FOR IFR WHERE DZ OR RA BEGINS. GOOD  
CONFIDENCE THAT RAIN WILL INCREASE LATE THIS AFTERNOON THROUGH  
TONIGHT. VSBYS WILL LOWER OVERNIGHT. 40$ CHANCE FOR LIFR VISBYS  
AFTER 03Z. MODERATE CONFIDENCE WITH WINDS AND FROPA.  
 
S OF POINT CONCEPTION...MODERATE CONFIDENCE THROUGH THIS AFTERNOON  
OR AROUND 02Z. 30% MVFR CIGS WILL DEVELOP THIS MORNING FOR COASTAL  
TAF SITES. LIGHT RAIN WILL OR DRIZZLE WILL DEVELOP LATE THIS  
EVENING...WITH MODERATE CONFIDENCE FOR HEAVIER RAIN TO DEVELOP  
AFTER 09Z-12Z. VISBYS WILL VARY WITHIN THE RAIN. FROM MVFR TO  
LIFR. MODERATE CONFIDENCE WITH FROPA EARLY THURSDAY MORNING.  
KLAX...MODERATE TO HIGH CONFIDENCE WITH 12Z TAF THAT MVFR  
CONDITIONS WILL SPREAD INTO KLAX BY 13-14Z THERE IS A 50 PERCENT  
CHANCE THAT MVFR CONDITIONS COULD LINGER THROUGHOUT THE DAY. EAST  
WIND COMPONENT SHOULD DEVELOP AFTER 03Z THIS EVE AND STAY BELOW 9  
KT BRIEFLY UNTIL 5-6Z. CONFIDENCE IS HIGH THAT SE WINDS WILL  
STRENGTHEN AHEAD OF THE FRONT FROM 06Z THROUGH AT LEAST 14Z WHEN  
SUSTAINED WINDS WILL REMAIN ABOVE 9 KT AND GUSTS OVER 15 MPH AT  
LEAST THROUGH 14Z WHEN THE FRONT PASSES. WINDS WILL THEN SHIFT TO  
THE S-SW BETWEEN 14-15Z. MODERATE CONFIDENCE THAT HEAVIER RAIN  
WILL DEVELOP AFTER 10Z AND CONTINUE THROUGH THE MORNING HOURS.  
WINDS WILL REMAIN OUT OF THE SW TO W THE REMAINDER OF THE PERIOD  
THROUGH 12Z THU.  
 
KBUR...MODERATE CONFIDENCE WITH 12Z TAF. EXPECT VSBYS TO LOWER  
WHEN HEAVIER RAINS BEGIN AFTER 06Z. MODERATE CONFIDENCE WITH  
FROPA TIMING.  
 

 
   
MARINE
 
18/830 AM.  
 
FOR ALL COASTAL WATERS NORTH OF POINT CONCEPTION...  
 
SMALL CRAFT ADVISORY (SCA) LEVEL WINDS WILL INCREASE LATER THIS  
MORNING. BY THIS AFTERNOON GALE WARNING LEVEL GUSTS ARE EXPECTED  
THROUGH EARLY THURSDAY MORNING.  
 
FOR THE SOUTHERN OUTER WATERS SOUTH OF POINT CONCEPTION...  
 
WINDS WILL INCREASE TO SCA LEVEL BY MID AFTERNOON THROUGH EARLY  
THURSDAY MORNING. THERE IS A FORTY PERCENT CHANCE OF GALE WARNING  
LEVEL WINDS FROM EARLY FRIDAY MORNING THROUGH SATURDAY AFTERNOON.  
THERE IS A SLIGHT CHANCE OF THUNDERSTORMS TONIGHT INTO THURSDAY  
AND AGAIN ON FRIDAY.  
 
FOR THE INNER WATERS SOUTH OF POINT CONCEPTION...  
 
SOUTHERLY WINDS WILL INCREASE TO SCA LEVEL WINDS THIS EVENING  
ACROSS THE SANTA BARBARA CHANNEL WITH THE STRONGEST WINDS  
BEGINNING ACROSS THE NORTHWEST PORTION. THERE IS A FORTY PERCENT  
CHANCE OF GALE WARNING LEVEL WINDS FROM FRIDAY MORNING THROUGH  
SATURDAY MORNING. THERE IS A SLIGHT CHANCE OF THUNDERSTORMS  
THURSDAY AND FRIDAY.  
 
LARGE SWELLS...  
 
A LARGE LONG PERIOD SWELL WILL ARRIVE IN THE COASTAL WATERS ON  
THURSDAY THEN ANOTHER BUT LARGER SWELL WILL ARRIVE FRIDAY NIGHT  
INTO SATURDAY. THIS SECOND SWELL WILL POTENTIALLY REACH HEIGHTS  
OF MORE THAN 20 FEET OVER THE NORTHERN OUTER WATERS LATE FRIDAY  
NIGHT INTO SATURDAY.  
 

 
   
LOX WATCHES/WARNINGS/ADVISORIES
 
 
CA...WIND ADVISORY IN EFFECT FROM 7 PM THIS EVENING TO 4 AM PST  
THURSDAY FOR ZONES 34>38-51-52. (SEE LAXNPWLOX).  
BEACH HAZARDS STATEMENT IN EFFECT FROM LATE TONIGHT THROUGH  
MONDAY EVENING FOR ZONES 34-35. (SEE LAXCFWLOX).  
BEACH HAZARDS STATEMENT IN EFFECT FROM THURSDAY MORNING  
THROUGH MONDAY EVENING FOR ZONES 39>41-87. (SEE LAXCFWLOX).  
WINTER WEATHER ADVISORY IN EFFECT FROM 10 PM THIS EVENING TO  
10 PM PST THURSDAY FOR ZONES 53-54. (SEE LAXWSWLOX).  
PZ...SMALL CRAFT ADVISORY IN EFFECT UNTIL 3 PM PST THIS AFTERNOON  
FOR ZONES 645-670-673. (SEE LAXMWWLOX).  
GALE WARNING IN EFFECT FROM 3 PM THIS AFTERNOON TO 3 AM PST  
THURSDAY FOR ZONES 645-670-673. (SEE LAXMWWLOX).  
SMALL CRAFT ADVISORY IN EFFECT FROM 9 PM THIS EVENING TO 9 PM  
PST THURSDAY FOR ZONE 650. (SEE LAXMWWLOX).  
GALE WATCH IN EFFECT FROM FRIDAY MORNING THROUGH SATURDAY  
MORNING FOR ZONE 650. (SEE LAXMWWLOX).  
GALE WATCH IN EFFECT FROM FRIDAY MORNING THROUGH SATURDAY  
AFTERNOON FOR ZONE 655. (SEE LAXMWWLOX).  
SMALL CRAFT ADVISORY IN EFFECT FROM 3 PM THIS AFTERNOON TO 3  
AM PST FRIDAY FOR ZONE 676. (SEE LAXMWWLOX).  
GALE WATCH IN EFFECT FROM LATE THURSDAY NIGHT THROUGH  
SATURDAY AFTERNOON FOR ZONE 676. (SEE LAXMWWLOX).  
 

 
   
HAZARD POTENTIAL OUTLOOK
 
(FRI-TUE)  
A WET AND UNSETTLED WEATHER PATTERN IS LIKELY FRIDAY THOUGH MONDAY.  
THE HEAVIEST RAIN DURING THIS PERIOD WILL PROBABLY FALL ON FRIDAY  
AND AGAIN SUNDAY INTO EARLY MONDAY. THERE IS A CHANCE OF DAMAGING  
WARNING LEVEL SURF AND COASTAL FLOODING ISSUES STARTING FRIDAY  
AND CONTINUING THROUGH SATURDAY, ESPECIALLY ALONG THE CENTRAL  
COAST.  
 

 
 

 
 
PUBLIC...MW/DB  
AVIATION...KAPLAN  
MARINE...KJ  
SYNOPSIS...STU  
 
WEATHER.GOV/LOSANGELES  
 
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