High Wind in California, December 22, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1000 PM PST MON DEC 21 2015

.SYNOPSIS....RAIN WILL CONTINUE TO SPREAD SOUTHWARD
ACROSS THE REGION THROUGH EARLY TUESDAY MORNING WITH SIGNIFICANT
RAINFALL LIKELY OVER THE COASTAL RANGES AND HIGHER ELEVATIONS.
ANOTHER WEAK SYSTEM WILL APPROACH FROM THE NORTH WEDNESDAY INTO
THURSDAY AND BRING LIGHT RAINFALL AND POTENTIALLY SNOWFALL TO THE
HIGHER ELEVATIONS THURSDAY INTO EARLY CHRISTMAS MORNING. DRIER AND
COLDER CONDITIONS ARE THEN EXPECTED CHRISTMAS DAY INTO THE
UPCOMING WEEKEND.

&&

.DISCUSSION...AS OF 9:00 PM PST MONDAY... WIDESPREAD RAINFALL
WAS OBSERVED ACROSS THE REGION TODAY IN RESPONSE TO A DEEP MOIST
PLUME OF ATMOSPHERIC MOISTURE AIMED AT THE REGION. MT TAMALPAIS
HAS CONTINUOUSLY SEEN THE HIGHEST AMOUNT OF RAIN OVER THE LAST FEW
DAYS DUE TO EXTREMELY FAVORABLE OROGRAPHICS/ISENTROPIC LIFT SUPPORTED
BY THE DEEP MOIST FLOW ALOFT. STORM TOTAL RAIN AT MIDDLE PEAK RAWS
ON TAMALPAIS HAS NOW EXCEEDED 7.5 INCHES... WITH MORE RAIN SET TO
COME SHORTLY. ELSEWHERE... STORM TOTALS OF 3 TO 6 INCHES IN THE
NORTH BAY AND SANTA CRUZ MOUNTAINS.... 2 TO 3 INCHES ALONG THE
COASTAL NORTH BAY... SAN FRANCISCO/OAKLAND... AND SANTA CRUZ
COASTLINE.. THE LOWEST VALUES HAVE COME IN THE SOUTHERN PORTIONS
OF MONTEREY AND SAN BENITO COUNTIES... HOWEVER RAIN IS CONTINUING
TO FALL THERE.

LATEST RADAR CURRENTLY SHOWS PRECIPITATION TAPERING OFF AND
PRIMARILY LINGERING OVER MONTEREY AND SAN BENITO COUNTIES THIS
EVENING. RAINFALL RATES HAVE DROPPED OFF FROM A THIRD OF AN INCH
OVER THE HIGHER TERRAIN A FEW HOURS AGO... DOWN TO A LITTLE MORE
THAN A TENTH OR TWO AN HOUR PRESENTLY. THOUGH IT IS DIFFICULT TO
SEE BENEATH THE RADAR BEAM IN THE NORTH BAY... SATELLITE DATA AND
SHORT TERM GUIDANCE SUGGESTS ANOTHER ROUND OF PRECIPITATION
ASSOCIATED WITH A COLD FRONTAL PASSAGE WILL BE MOVING OVER THE
NORTH BAY AND EVENTUALLY SOUTHWARD AS MOISTURE CONTINUES TO STREAM
INTO TO THE REGION SHORTLY AND PERSISTING INTO TUESDAY MORNING.

WEST WINDS ARE EXPECTED TO PICK UP OVERNIGHT AS AN ENERGETIC UPPER
LEVEL JET APPROACHES ALOFT. THE STRONGEST WINDS ARE EXPECTED
OVER THE NORTH BAY MOUNTAINS AND EAST BAY HILLS WHERE PEAK GUSTS
OF 50 TO 60 MPH WILL BE POSSIBLE AROUND SUNRISE. WINDS WILL THEN
SHIFT FURTHER TO THE NORTHWEST AND GRADUALLY DECLINE THROUGH
TUESDAY. BREEZY CONDITIONS CAN BE EXPECTED ELSEWHERE. SEE THE
ISSUED WIND ADVISORY FOR ADDITIONAL DETAILS.

WIDESPREAD PRECIPITATION WILL TRANSITION INTO ISOLATED TO
SCATTERED SHOWERS BY TUESDAY AFTERNOON BEFORE DRIER WEATHER TAKES
HOLD ON WEDNESDAY. FORECAST MODELS CONTINUE TO SHOW A COLD...
ENERGETIC STORM SYSTEM DESCENDING RAPIDLY INTO THE GREAT BASIN ON
CHRISTMAS EVE. THIS STORM SYSTEM WILL BRING ANOTHER ROUND OF RAIN
FOR US... ALBEIT LESS THAN WE HAVE EXPERIENCED IN THE LAST 24
HOURS... WITH BREEZY WINDS AND MUCH COLDER TEMPERATURES. SNOW
LEVELS WILL DESCEND RAPIDLY IN THE POST FRONTAL ENVIRONMENT
MEANING SNOW SHOWERS WILL BE POSSIBLE OVER 2500-3500 FT. THE
ARCTIC AIR WILL ALSO PLUNGE OVERNIGHT LOWS TO NEAR TO SUB FREEZING
LEVELS FOR AT LEAST A FEW NIGHTS. DRIER WEATHER IS THEN EXPECTED
INTO THE WEEKEND.

.PREVIOUS DISCUSSION...AS OF 02:55 PM PST MONDAY...WIDESPREAD
PRECIPITATION CONTINUES OVER THE REGION THIS AFTERNOON AS A DEEP
MOISTURE PLUME CONTINUES TO ADVECT INTO NORTHERN CALIFORNIA. PWAT
VALUES ARE ESTIMATED AT AROUND 1.25" AT THIS HOUR AND ARE FORECAST
TO BE AS HIGH AS 1.35" BY THE NAM AND GFS MODELS AS THE
ATMOSPHERIC RIVER SLIDES DOWN THE COAST TONIGHT. THE HEAVIEST
RAINFALL CURRENTLY REMAINS TO THE NORTH OF MONTEREY AND SAN BENITO
COUNTIES WHERE RAINFALL RATES OF 0.25" TO NEARLY 0.50" ARE BEING
REPORTED IN THE COASTAL RANGES. THIS HEAVIER PRECIPITATION WILL
CONTINUE TO SHIFT SOUTHWARD THROUGH THE REMAINDER OF THE DAY AND
INTO THE OVERNIGHT HOURS AS A COLD FRONT DIVES INTO NORTHERN
CALIFORNIA. GIVEN THIS MOISTURE TAP AND STRONG ISENTROPIC FLOW OF
40 TO 50 KTS, RAINFALL AMOUNTS OF 1" TO 3" WITH ISOLATED AMOUNTS
UP TO 5" CAN BE EXPECTED IN THE NORTH BAY MOUNTAINS, DOWN THE
COASTAL RANGES AND OVER THE EAST BAY HILLS THROUGH EARLY TUESDAY
MORNING. MEANWHILE, RAINFALL AMOUNTS OVER THE INLAND VALLEYS WILL
BE MUCH LESS DUE TO RAIN SHADOWING. ADDITIONAL RAINFALL OVER THE
NORTH BAY VALLEYS WILL RANGE BETWEEN 0.50" TO 1" AND BETWEEN 0.50"
TO 0.75" AROUND THE SAN FRANCISCO BAY. FURTHER SOUTH AND INLAND
CAN EXPECTED BETWEEN 0.25" TO 0.50" INCHES. IN WAKE OF THE FRONTAL
PASSAGE LATE THIS EVENING, WEST TO NORTHWEST WINDS WILL INCREASE
OVER MUCH OF THE REGION WITH THE STRONGEST WINDS SPEEDS EXPECTED
OVER THE NORTH BAY AND EAST BAY MOUNTAINS/HILLS. WIND SPEEDS OF 20
TO 30 MPH WITH GUSTS UP TO 50 MPH CAN BE EXPECTED TONIGHT INTO
EARLY TUESDAY AFTERNOON. THUS, A WIND ADVISORY HAS BEEN ISSUED FOR
THESE LOCATIONS. ELSEWHERE, ESPECIALLY NEAR THE COAST, BREEZY
CONDITIONS WITH LOCALLY HIGHER GUSTS WILL ALSO BE POSSIBLE.

PRECIPITATION WILL TAPPER OFF FROM NORTH TO SOUTH ON TUESDAY WITH
LINGERING SHOWERS POSSIBLE IN THE AFTERNOON AND EARLY EVENING.
OVERALL, ADDITIONAL RAINFALL AMOUNTS WILL BE LIGHT AND ISOLATED IN
NATURE. WHILE WE CANNOT RULE OUT A FEW SHOWERS ON WEDNESDAY, MOST
OF REGION WILL REMAIN DRY AHEAD OF OUR NEXT APPROACHING SYSTEM.
THIS SYSTEM WILL BRING RAIN CHANCES BACK TO THE NORTHERN HALF OF
THE REGION WEDNESDAY NIGHT AND DOWN ACROSS THE SOUTHERN HALF ON
THURSDAY. THE MOISTURE ASSOCIATED WITH THE WEDNESDAY/THURSDAY
SYSTEM WILL BE MUCH LESS (AROUND HALF) COMPARED TO TODAY'S
ATMOSPHERIC RIVER. A MUCH COOLER AIR MASS WILL ALSO FILTER DOWN
INTO THE REGION WITH SNOW LEVELS FALLING TO AROUND 2500 FEET LATE
THURSDAY INTO FRIDAY. WITH LINGERING MOISTURE IN PLACE AND SHOWERS
POSSIBLE INTO CHRISTMAS DAY, CANNOT RULE OUT SNOW FALL AT OR ABOVE
2500 FEET THURSDAY EVENING INTO FRIDAY MORNING. A COLDER AND DRIER
AIR MASS IS EXPECTED TO REMAIN OVER THE REGION FROM FRIDAY INTO
THE WEEKEND WITH OUR NEXT POTENTIAL SYSTEM (ALBEIT WEAK)
APPROACHING NORTHERN CALIFORNIA LATE SUNDAY INTO MONDAY.

&&

.AVIATION...AS OF 9:58 PM PST MONDAY...WET WEATHER WITH MVFR
CIGS/VSBYS AND LOCALIZED IFR CIGS/VSBYS. WX OBSCURING MTNS/HILLS.
A COLD FRONT OVER NW CA WILL SLIDE SE OVER THE AREA TUESDAY
REACHING THE NORTH BAY TUESDAY MORNING THEN THE NORTH CENTRAL
COAST EITHER LATE TUESDAY AFTERNOON OR EVENING. A COLDER UPPER
LEVEL TROUGH ARRIVES TUESDAY NIGHT INTO WEDNESDAY.

VICINITY OF KSFO...MVFR CIGS/VSBYS. RAIN TONIGHT BECOMING SHOWERY
TUESDAY.

SFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...MVFR CIGS/VSBYS LOCALIZED IFR AT TIMES.

&&

.MARINE...AS OF 07:44 PM PST MONDAY...A PASSING STORM SYSTEM WILL
BRING GUSTY WINDS...PERIODS OF RAIN AND ROUGHER SEAS THROUGH
TUESDAY. WINDS DECREASE WEDNESDAY...BUT ANOTHER STORM SYSTEM WILL
INCREASE WINDS ON THURSDAY AS A LARGER SWELL ENTERS THE COASTAL
WATERS.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
 .TDAY...WIND ADVISORY...NORTH BAY MTNS & EAST BAY HILLS & DIABLO RANGE
         SCA...MRY BAY SCA...PIGEON PT TO PT PINOS 0-10 NM
         SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
         SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
         SCA...SF BAY
         SCA...PT ARENA TO PT REYES 0-10 NM
         SCA...PT REYES TO PIGEON PT 0-10 NM
         SCA...PT ARENA TO PIGEON PT 10-60 NM
 SCA...ROUGH BAR ADVISORY FOR SF BAR UNTIL 3 PM

&&

PUBLIC FORECAST: DRP
AVIATION: CANEPA
MARINE: MM

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