000
FXUS66 KSGX 261652
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
852 AM PST THU DEC 26 2019

.SYNOPSIS...
A LOW PRESSURE SYSTEM MOVING ACROSS THE SOUTHERN CALIFORNIA
COASTAL WATERS, WILL KEEP UNSETTLED AND WINTERY WEATHER OVER THE 
REGION TODAY. SCATTERED SHOWERS WILL CONTINUE WEST OF THE MOUNTAINS, 
WHILE MODERATE RAIN CONTINUES IN THE LOWER DESERTS AND SNOW 
FALLS IN THE MOUNTAINS AND PORTIONS OF THE HIGH DESERTS. THE STORM 
WILL MOVE EAST ON FRIDAY, ENDING THE RAIN AND SNOW. THE WEEKEND WILL 
BE DRY AND A LITTLE WARMER. ANOTHER LOW PRESSURE SYSTEM FROM THE 
NORTH COULD BRING MORE PRECIPITATION EARLY NEXT WEEK WITH WARMING
AND DRYING FOR THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

RADAR SHOWS THE HEAVIEST PRECIPITATION HAS NOW SHIFTED EAST TOWARD 
THE MTS/DESERTS. SNOW LEVELS HAVE BEEN AROUND 2500 FT. STORM PRECIP 
TOTALS HAVE BEEN POSTED AND ARE HEADLINED ON OUR WEBPAGE. UP TO 2.5 
INCHES HAS FALLEN IN O.C., WITH ABOUT 1.5 IN WESTERN SAN DIEGO 
COUNTY. SOME SNOW AMOUNTS HAVE BEEN GATHERED AS WELL WITH MOST ON 
PALOMAR MTN(10 INCHES) AND WRIGHTWOOD (15 INCHES). A DETAILED 
HYDROLOGY DISCUSSION HAS BEEN UPDATED BELOW. 

WATER VAPOR IMAGERY SHOWS THE UPPER LOW CENTER IS JUST SW OF PT. 
CONCEPTION BUT THERE ARE TWO WELL DEFINED DISTURBANCES ROTATING 
AROUND IT. ONE IS ABOUT 160 MILES SW OF SAN DIEGO AND THE OTHER IS 
235 MILES WEST. THE LATEST 12Z NAM12 RUNS SWING THESE BOTH INTO 
NORTHERN BAJA TODAY AND TONIGHT AS THE PARENT UPPER LOW MOVES OVER 
SAN DIEGO COUNTY. BOTH HELP TO PIVOT THE CIRCULATION AND CONCENTRATE 
AREAS OF LIFT AND HEAVIER PRECIP. THE DISTURBANCE TO THE WEST WILL 
PROLONG THE CYCLONIC FLOW OVER THE AREA, WHILE THE ONE TO THE SW 
ROTATES NORTH AND HELPS TO SET UP A WRAP-AROUND BAND OF MODERATE 
PRECIPITATION. THAT WILL NEED TO BE EVALUATED FURTHER, AS IT NOW 
LOOKS LIKE IT COULD HIT NORTHERN PARTS OF THE CWA PRETTY HARD BY THIS 
EVENING WITH MODERATE/HEAVY SNOW.  

THE WIND ADVISORY HAS BEEN CANCELLED SINCE THE POTENTIAL FOR ANY 
ADDITIONAL STRONG WINDS WEST OF THE MOUNTAINS HAS DIMINISHED. THE
FORECAST HAS BEEN UPDATED THIS MORNING.

FROM PREVIOUS DISCUSSION...

ADJUSTMENTS TO THE FORECAST ARE MOSTLY DUE TO THE NORTHWARD SHIFT
IN THE TRACK OF THE STORM MOVING ACROSS SOUTHERN CALIFORNIA NOTED
LAST NIGHT. THIS WILL SHIFT THE WRAP AROUND PRECIPITATION FARTHER
NORTH FOR LATER THIS AFTERNOON AND TONIGHT. SNOWFALL IN THE SAN 
BERNARDINO COUNTY MOUNTAINS WILL BE ABOUT AS EXPECTED BUT HAS 
TRENDED LOWER FARTHER SOUTH, ESPECIALLY IN THE SAN DIEGO COUNTY 
MOUNTAINS.

MUCH OF THE PRECIPITATION FOR ORANGE AND SAN DIEGO COUNTIES AND 
THE INLAND EMPIRE WILL BE WITH THE COLD FRONTAL PRECIPITATION BAND
AS IT MOVES ACROSS THE AREA THIS MORNING, CONTINUING INTO EARLY 
AFTERNOON IN THE MOUNTAINS AND DESERTS. 

FOR LATER THIS AFTERNOON INTO TONIGHT, THE AREAS RECEIVING 
ADDITIONAL MORE WIDESPREAD PRECIPITATION WILL BE PRIMARILY THE 
MOUNTAINS AND DESERTS OF SAN BERNARDINO AND RIVERSIDE COUNTIES 
WITH PRECIPITATION GENERALLY LIGHTER AND MORE WIDELY SCATTERED 
ELSEWHERE. PRECIPITATION IS EXPECTED TO END EARLY FRIDAY AS THE 
LOW PRESSURE SYSTEM MOVES ON TO THE EAST.

FOR COASTAL AREAS, TOTAL RAINFALL IS EXPECTED TO RANGE FROM 2 TO
2.5 INCHES FOR ORANGE COUNTY WITH LOCALLY GREATER AMOUNTS, WITH 
GENERALLY 1.5 TO 2 INCHES FOR SAN DIEGO COUNTY. AMOUNTS ARE 
EXPECTED TO LESSEN ACROSS THE VALLEYS TO AROUND 1 INCH IN THE FAR 
INLAND VALLEYS. IN THE SAN BERNARDINO COUNTY MOUNTAINS, LIQUID 
EQUIVALENT AMOUNTS OF 2 TO 4 INCHES ARE EXPECTED WITH LOCALLY 
GREATER AMOUNTS. IN THE MOUNTAINS OF RIVERSIDE AND SAN DIEGO 
COUNTIES, LIQUID EQUIVALENT AMOUNTS WILL GENERALLY RANGE FROM 1 TO
1.5 INCH WITH LOCAL AMOUNTS TO AROUND 2 INCHES. DESERT AREAS WILL
RECEIVE AROUND AN INCH. PEAK HOURLY RAINFALL RATES OF ONE HALF 
PER HOUR ARE EXPECTED THIS MORNING, LOCALLY TO ONE INCH PER HOUR.

THE GREATEST RAINFALL OVERNIGHT FOR COASTAL AREAS HAS BEEN IN
NORTHWESTERN ORANGE COUNTY WITH 2 TO 2.5 INCHES. THE PLUME OF
SUBTROPICAL MOISTURE WITH PRECIPITABLE WATER VALUES TO 0.9 INCH
THAT HAS FED THE COLD FRONTAL PRECIPITATION BAND OVERNIGHT IS
EXPECTED TO BE SUPPRESSED TO THE SOUTH DURING THE MORNING WITH
RAINFALL TOTALS TRENDING LESS FARTHER INLAND AND TO THE SOUTH AS
THIS PRECIPITATION BAND MOVES INLAND.

A BAND OF INSTABILITY WITH MOST UNSTABLE CAPE VALUES OF 500 TO 
1000 J/KG HAS BEEN AT THE LEADING EDGE OF THE FRONT AS IT NEARS 
THE COAST. THE NAM SHOWS IT DECREASING FROM NORTH TO SOUTH AS IT 
REACHES THE COAST. THERE HAVE BEEN BANDS OF MORE INTENSE SHOWERS 
OVER THE COASTAL WATERS WITH THIS INSTABILITY ALONG WITH A FEW 
THUNDERSTORMS, AHEAD OF THE FRONT, THE LOWER LEVEL VERTICAL SHEAR 
IS FAVORABLE FOR STORM ROTATION AND THERE HAVE BEEN OCCASIONAL 
ROTATING CELLS OVER THE COASTAL WATERS GOING BACK TO AROUND 10 PM 
YESTERDAY EVENING OFF THE ORANGE COUNTY. WHILE THERE HAVE BEEN NO
REPORTS OF WATERSPOUTS SO FAR, IT IS LIKELY THAT AT LEAST SOME OF
THESE CELLS PRODUCED WATERSPOUTS.

PRECIPITATION IS EXPECTED TO END EARLY FRIDAY WITH DRY AND A
LITTLE WARMER WEATHER FOR THE WEEKEND. FOR EARLY NEXT WEEK,
ANOTHER LOW PRESSURE SYSTEM MOVING SOUTHWARD ALONG THE WEST COAST
IS EXPECTED TO DEVELOP INTO A CLOSED LOW AS IT MOVES ACROSS
CALIFORNIA. THERE REMAINS SOME SPREAD AMONG THE MODEL TRACK
FORECASTS. IT SHOULD BRING MORE COOLING AND ANOTHER CHANCE FOR
PRECIPITATION. JUST WHERE AND HOW MUCH IS TRACK DEPENDENT. POPS
HAVE BEEN INCREASED FOR MONDAY INTO TUESDAY SIMILAR IN LINE WITH 
THE NBM.

&&

.AVIATION...
261100Z...WIDESPREAD RAIN AT LOWER ELEVATIONS AND SNOW IN THE 
MOUNTAINS TO CONTINUE THROUGH 20Z THURSDAY. RAIN AND SNOW COULD BE 
HEAVY AT TIMES THROUGH 16Z. SCT-BKN CLOUDS WILL BE VARIABLE, WITH 
BASES BETWEEN 3000-5000 FT MSL. IN HEAVIER RAIN, BASES WILL LOWER TO 
1500-3000 FT MSL WITH VIS REDUCED DOWN TO 2-4 MILES. HIGHER TERRAIN 
WILL BE OBSCURED AT TIMES THROUGH TODAY. GUSTY SOUTHEAST WINDS 
GUSTING 15-25 KTS, WITH ISOLATED GUSTS TO 40 KTS OVER HIGHER TERRAIN 
LIKELY THROUGH 16Z. AFTER 20Z, WIDESPREAD RAIN WILL TAPER OFF TO 
SHOWERS.

&&

.MARINE... 
STRONG SOUTH TO SOUTHEAST WINDS WILL CONTINUE TO MOVE THROUGH THE 
REGION THIS MORNING. WIDESPREAD WIND GUSTS TO 30 KT ARE EXPECTED 
OVER THE WATERS WITH SOME GUSTS AROUND 35 KT LIKELY WITH THE FRONTAL 
PASSAGE THROUGH 5 AM. WIND DIRECTIONS WILL BE SOMEWHAT VARIABLE 
DURING THE DAY THURSDAY BUT GUSTS TO 30 KT WILL BE POSSIBLE AT TIMES 
DURING THE DAY. COMBINED SEAS DUE TO BOTH THE LONG-PERIOD WEST SWELL 
AND THE CHOPPY WIND WAVES COULD REACH 10 FEET LATE THROUGH EARLY 
THIS MORNING. A GALE WARNING IS IN EFFECT THROUGH 2 PM TODAY. THERE 
IS ALSO A SLIGHT CHANCE OF A THUNDERSTORM WITH CLOUD-TO-WATER 
LIGHTNING STRIKES THROUGH EARLY THIS MORNING. 

THEREAFTER, NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED FRIDAY 
THROUGH TUESDAY. 


&&

.HYDROLOGY...UPDATED
COASTAL AREAS...THE HEAVIEST, WIDESPREAD PRECIPITATION HAS MOVED OUT 
OF COASTAL AREAS AS OF 8 AM PST BUT CONTINUES OVER PORTIONS OF THE 
MOUNTAINS AND DESERTS. ANY FURTHER ACTIVITY WEST OF THE MOUNTAINS 
TODAY WILL BE IN THE FORM OF SCATTERED SHOWERS. OVERALL, FURTHER 
ACCUMULATIONS WILL BE LIGHT. HOWEVER, THERE WILL BE A CHANCE OF 
LOCALIZED, HEAVIER SHOWERS/THUNDERSTORMS INTO LATE AFTERNOON UNDER 
THE COLD UPPER LOW CENTER. RUNOFF WILL CONTINUE TO SWELL CREEKS AND 
RIVERS. NO RIVER FLOODING IS EXPECTED, ALTHOUGH THE SAN DIEGO 
RIVER....

MOUNTAINS/HIGH DESERT...MODERATE TO HEAVY SNOWFALL RATES WILL 
CONTINUE OVER THE SAN DIEGO COUNTY MTS THROUGH LATE MORNING THEN 
TAPER OFF. SNOW LEVELS ARE NEAR 2500 FT SO RUNOFF WILL BE LIMITED. 
FARTHER NORTH, THE RIVERSIDE COUNTY MTS WILL SEE A DECREASE IN RATES 
OF SNOWFALL BY EARLY AFTERNOON, AGAIN WITH VERY LOW SNOW LEVELS AND 
LIMITED RUNOFF. IN SAN BERNARDINO COUNTY, SNOWFALL RATES SHOULD 
TAPER THIS AFTERNOON BUT WILL LIKELY CONTINUE THROUGH THE DAY AND 
MAY INCREASE AGAIN THIS EVENING. THE HIGH DESERTS WILL CONTINUE TO 
SEE RAIN AND SNOWFALL THROUGH THE DAY AND TONIGHT. SNOWFALL COULD 
GET HEAVY BY NIGHTFALL. MOST AREAS WILL LIKELY HAVE SNOWFALL 
ACCUMULATION OF FIVE INCHES OR MORE AS LOW AS 3000 FT.

LOWER DESERTS...MODERATE TO HEAVY RAIN WILL CONTINUE THROUGH THE 
MORNING AND TAPER THIS AFTERNOON. A NORTHWARD SHIFT OF THE STORM 
TRACK HAS REDUCED EXPECTED STORM TOTALS TO AROUND ONE INCH. SOME 
URBAN/DRY WASH FLOODING IS STILL POSSIBLE AND THE COACHELLA CANAL IS 
LIKLEY TO HAVE FLOW AS WELL WHICH MAY IMPACT LOW-WATER CROSSINGS.

&&

.SKYWARN... 
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
 ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.


&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...WINTER STORM WARNING UNTIL 6 PM PST THIS EVENING FOR SAN DIEGO 
     COUNTY MOUNTAINS.

     WINTER STORM WARNING UNTIL 6 AM PST FRIDAY FOR SAN BERNARDINO 
     COUNTY MOUNTAINS.

     WINTER WEATHER ADVISORY UNTIL 6 AM PST FRIDAY FOR APPLE AND 
     LUCERNE VALLEYS.

     WINTER STORM WARNING UNTIL 6 AM PST FRIDAY FOR RIVERSIDE COUNTY 
     MOUNTAINS.

PZ...GALE WARNING UNTIL 2 PM PST THIS AFTERNOON 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...10/17
AVIATION/MARINE...APR

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