Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 242118
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
218 PM PDT FRI OCT 24 2014

.SYNOPSIS...A COLD FRONT WILL APPROACH THE COAST LATER TONIGHT
INCREASING SOUTH WINDS AND RAIN CHANCES. THE FRONT WILL PASS
THROUGH QUICKLY IN THE MORNING...BUT COOLER UNSTABLE AIR WILL BRING
SHOWERS TO MUCH OF THE AREA SATURDAY AFTERNOON AND EVENING. A FEW
THUNDERSTORMS MAY DEVELOP ESPECIALLY SANTA CRUZ MOUNTAINS
NORTHWARD. DRIER AND COOLER WEATHER IS EXPECTED SUNDAY WITH A
WARMING TREND BEGINNING MONDAY AS HIGH PRESSURE REBUILDS ALONG THE
COAST.

&&

.DISCUSSION...AS OF 01:29 PM PDT FRIDAY...OFFSHORE WINDS HAVE
TURNED TO SOUTHERLY AS A FORERUNNER TO THE APPROACHING COLD FRONT
AND MARINE LAYER DEEPENING AND STARTING TO MIX OUT. COLD CORE
TROF LOCATED AROUND 135W WITH VORT CENTER AROUND 35N AND HAS
BOTTOMED OUT. FEATURE WILL PROGRESS EASTWARD AND SHEAR TO THE
NORTHEAST AS IT MOVES ONSHORE SATURDAY. GIVEN EXTENT OF COLD FRONT
TO THE SOUTH...BELIEVE THIS SYSTEM WILL PRODUCE RAINFALL ACROSS
MOST OF THE AREA WITH THE HEAVIEST PRECIPITATION IN THE NORTH BAY
AND SANTA CRUZ MOUNTAINS NORTHWARD. AMOUNTS WILL VARY CONSIDERABLY
WITH LESS THAN A TENTH OF AN INCH MOST OF MONTEREY COUNTY TO AS
MUCH AS THREE QUARTERS INCH NORTH BAY MOUNTAINS.

MAIN METEOROLOGICAL CONCERNS WILL BE SIGNIFICANT PRE FRONTAL SOUTH
WINDS ALONG THE COAST AND HIGHER ELEVATIONS OF COASTAL MOUNTAINS.
PLANNING ON ISSUING WIND ADVISORY FOR THESE AREAS LATE TONIGHT AND
SATURDAY MORNING. HIGHER RESOLUTION NAM AND WRF MODELS INDICATE
QUICK FRONTAL PASSAGE INTO THE BAY AREA EARLY IN THE MORNING AND
THROUGH THE REST OF THE DISTRICT BY EARLY AFTERNOON. COOL UNSTABLE
AIRMASS IN THE WAKE OF THE COLD FRONT WILL TRIGGER CONVECTION WITH
POSSIBLE THUNDERSTORMS SANTA CRUZ MOUNTAINS NORTHWARD. SHOULD SEE
A BRIEF LULL IN PRECIP AFTER THE COLD FRONT...THEN SATURDAY
AFTERNOON AND EVENING SHOULD BE ACTIVE WITH CONVECTION.

BELIEVE THE NAM IS A LITTLE OVERDONE WITH HIGH CAPE AND HELICITY
VALUES...BUT GFS IS LIKELY UNDERDONE WITH LOWER MODEL RESOLUTION
ISSUES. INTERESTING TO NOTE THAT UNUSUALLY WARM SEA SURFACE
TEMPERATURES COULD ASSIST CONVECTIVE DEVELOPMENT SATURDAY
AFTERNOON AS THE COOLER AIRMASS MOVES OVERHEAD. CONFIDENCE IN
CONVECTIVE STRENGTH IS LOW...BUT CONFIDENCE IS MODERATE FOR A
THUNDERSTORM OR TWO AT LEAST NORTH BAY.

DYNAMICS WITH THIS SYSTEM ARE NOT PARTICULARLY IMPRESSIVE
WITH AN APPARENT STABLE LAYER ABOVE 700 MB THAT SHOULD CAP ANY
SIGNIFICANT CONVECTION. HOWEVER...IF DEW POINTS STAY HIGH
ENOUGH...WOULD BE ABLE TO BREAK THROUGH THIS STABLE LAYER ALOFT.

THE COOLEST DAY SHOULD BE SUNDAY WITH NORTHWEST FLOW AND THE
AIRMASS WILL BEGIN TO DRY OUT. MODEL TRENDS ARE LEANING TOWARD
STRONGER HIGH PRESSURE NEXT WEEK KEEPING THE JET STREAM WELL TO
OUR NORTH. LOOK FOR DRIER AND WARMER CONDITIONS THROUGH MIDWEEK.
COULD BE A FEW SHOWERS EXTREME NORTH BAY AS WEAK SYSTEMS PUSH THRU
THE PACIFIC NW. LOTS OF DIFFERENCES IN THE MEDIUM RANGE GUIDANCE
LATE NEXT WEEK WITH A TREND TOWARD SLOWER APPROACH OF NEXT TROF
AND DELAYING NEXT SIGNIFICANT THREAT FOR RAIN UNTIL AT LEAST NEXT
WEEKEND.

&&

.AVIATION...AS OF 10:52 AM PDT FRIDAY...FOR 18Z TAFS. NO CONCERNS
FOR THIS AFTERNOON WITH MAINLY CLEAR SKIES AND SOME LIGHT
SOUTHERLY WINDS DEVELOPING BUT THEY SHOULD TREND SOUTHWEST THIS
AFTERNOON. FAIRLY IMPRESSIVE LOW WILL DEEPEN OFF THE COAST LATER
THIS AFTERNOON AND EVENING WITH INCREASING SOUTHEAST FLOW
DEVELOPING LATER THIS EVENING AND OVERNIGHT. PRETTY HIGH
CONFIDENCE FOR STRONG SOUTHEAST WINDS AND WET RUNWAYS FOR SATURDAY
MORNING. T-STORMS EVEN POSSIBLE SATURDAY AFTERNOON BUT WONT SHOW
THAT IN TAF AT THIS TIME.

VICINITY OF KSFO...VFR SKIES THIS AFTERNOON AND EVENING. LIGHT
SOUTHEAST WINDS THROUGH EARLY AFTERNOON SHOULD TREND SOUTHWEST AND
NOT IMPACT OPERATIONS. INCREASING SOUTHEAST WINDS OVERNIGHT WILL
LIKELY CAUSE ISSUES FOR SATURDAY MORNING PLANNING.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...CLEAR FOR KSNS THIS AFTERNOON WITH
CLOUD BANK CURRENTLY HOVERING OVER KMRY. EXPECT PARTIAL CLEARING
AT THE COAST. SOUTHERLY WINDS SHOULD DEVELOP OVERNIGHT WITH SOME
-SHRA BY AROUND 12-15Z SATURDAY.

&&

.MARINE...AS OF 10:52 AM PDT FRIDAY...HIGH PRESSURE OFF THE
SOUTHERN CALIFORNIA COAST WILL WEAKEN AS A DEEPENING LOW PRESSURE
SYSTEM APPROACHES FROM THE WEST.  THE LOW WILL LIFT NORTHEAST ON
SATURDAY MOVING INLAND OVER THE PACIFIC NORTHWEST SATURDAY NIGHT.
SOUTH WINDS WILL INCREASE TODAY THROUGH SATURDAY THEN SWITCH TO
NORTHWEST SATURDAY NIGHT AND SUNDAY. THE LOW WILL BRING A SLIGHT
CHANCE OF THUNDERSTORMS TO THE NORTHERN WATERS SATURDAY.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
             WIND ADVISORY...CAZ505-507-509-512-529 FROM 3 AM UNTIL
                             NOON SATURDAY
             SCA...SF BAY NORTH OF THE BAY BRIDGE FROM 3 AM
             SCA...SF BAY SOUTH OF THE BAY BRIDGE FROM 3 AM
             SCA...PIGEON PT TO PT PINOS 0-10 NM FROM 3 AM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM FROM 3 AM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 10-60 NM FROM 3 AM
             SCA...PT ARENA TO PT REYES 0-10 NM FROM 9 PM
             SCA...PT REYES TO PIGEON PT 0-10 NM FROM 9 PM
             SCA...PT ARENA TO PT REYES 10-60 NM FROM 9 PM
             SCA...PT REYES TO PIGEON PT 10-60 NM FROM 9 PM
             SCA...PIGEON PT TO PT PINOS 10-60 NM FROM 9 PM
             SCA...ROUGH BAR ADVISORY FOR SF BAR FROM 5 AM

&&

$$

PUBLIC FORECAST: KBB
AVIATION/MARINE: RWW

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