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

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000
FXUS66 KMTR 210018
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
518 PM PDT MON APR 20 2015

.SYNOPSIS...A DEEP MARINE LAYER WILL ALLOW LOW CLOUDS TO SPREAD
WELL INLAND DURING THE NIGHT AND MORNING HOURS ACROSS THE BAY AREA
THE NEXT FEW DAYS KEEPING TEMPERATURES NEAR OR SLIGHTLY BELOW
NORMAL. AN UPPER LOW OVER THE REGION MAY GENERATE SOME NIGHT AND
MORNING DRIZZLE ALONG WITH SOME AFTERNOON CUMULUS BUILD-UPS OVER
THE REMOTE INTERIOR HILLS THE COULD LEAD TO AN OUTSIDE CHANCE OF A
STRAY SHOWER OR ISOLATED THUNDERSTORM.

&&

.DISCUSSION...AS OF 2:58 PM PDT MONDAY...DEEP 2500 FOOT MARINE
LAYER IN PLACE WITH SFO-SAC ONSHORE FLOW CURRENTLY 2.8 MB KEEPING
ONSHORE WINDS STRONG THROUGH THE DELTA. TEMPERATURES IN THE CITY
AND HERE AT THE OFFICE IN MONTEREY CURRENTLY A COOL 57 AS OF 2 PM
WITH LIVERMORE ONLY 71 WITH A 15 MPH WEST WIND. CONVECTION HAS
FIRED ACROSS MOST OF THE HIGHER MOUNTAINS ACROSS THE STATE WITH
DEBRIS CLOUDS OFF THE SIERRA CURRENTLY ROTATING IN AN EAST TO WEST
DIRECTION DUE TO THE CIRCULATION OF LOW PRESSURE OVER SOUTHERN
CALIFORNIA AND A WEAK UPPER HIGH OVER OREGON. NOT OUT OF THE
QUESTION THAT A FEW HIGH LEVEL DEBRIS CLOUDS COULD DRIFT OVER THE
EAST BAY BY LATER THIS EVENING. SO FAR ONLY SOME CUMULUS CLOUDS
HAVE DEVELOPED OVER THE HIGHEST INTERIOR HILLS OF SAN BENITO
COUNTY THIS AFTERNOON WHICH MODELS HAVE HANDLED FAIRLY WELL.

LOOKING AHEAD...EXPECT THE MARINE LAYER TO STAY AT LEAST 2500 FEET
DEEP TONIGHT AND MAY EVEN APPROACH 3000 FEET ALLOWING FOR ANOTHER
DEEP INLAND PUSH OF MARINE CLOUDS BY TUESDAY MORNING. IN GENERAL
JUST GOING WITH A PERSISTENCE FORECAST IN TERMS OF TEMPERATURE ON TUESDAY.

IN GENERAL THE MODELS HAVE KEPT BACKING OFF ON ANY SHOWER CHANCES
FOR OUR CWA THE NEXT SEVERAL DAYS AS AN UPPER LEVEL TROUGH
APPROACHES WHILE AFTERNOON CONVECTION LOOKS TO OCCUR EACH DAY OVER
THE SIERRA AND NORTHERN MOUNTAINS. HAVE MAINTAINED SOME VERY LOW
AFTERNOON SHOWER/T-STORM CHANCES OVER THE HIGHER TERRAIN OF SAN
BENITO COUNTY AND ALONG THE NAPA/LAKE COUNTY BORDER. HOWEVER FOR
THE MAJORITY OF FOLKS THE MAIN WEATHER THEME WILL BE A MORE
TYPICAL NIGHT AND MORNING LOW CLOUD DECK CLEARING BACK TO THE
COAST TYPE OF FORECAST.

UNFORTUNATELY THE LONG RANGE MODELS HAVE BACKED OFF ON ANY
APPRECIABLE RAIN CHANCES FOR OUR CWA. THE 12Z ECMWF NOW BUILDS A
RIDGE OVER THE BAY AREA THIS WEEKEND AS AN INSIDE SLIDER DIVES
INTO NEVADA ON SATURDAY MORNING. SO IF ANYTHING THE TREND FOR THE
WEEKEND LOOKS WARMER WITH INCREASED COASTAL SUNSHINE.

GIVEN THE TRENDS ON ECMWF/CMC AND GFS MODELS HAVE PULLED POPS FROM
THE LONG RANGE FORECAST THAT PREVIOUSLY INCLUDED SLIGHT CHANCE OF
RAIN FOR THE NORTH BAY.

&&

.AVIATION...AS OF 5:00 PM PDT MONDAY...MAINLY CLEAR SKIES PREVAIL
OVER MOST TERMINALS WITH THE EXCEPTION OF KMTR AND KSNS. STRATUS
WILL MAKE AN EARLY RETURN TONIGHT WITH LOW CLOUDS EXPECTED TO
PUSH INLAND AROUND 03Z-04Z THIS EVENING. BORDERLINE IFR/MVFR CIGS
EXPECTED. ONSHORE WINDS WILL BE GUSTY ALONG THE EDGES OF THE
STRATUS FIELD AS WELL AS THROUGH AREAS WHERE THE WIND IS FUNNELED
THROUGH COASTAL GAPS. SPEEDS SHOULD CONTINUE AROUND 10 TO 15 KT
WITH GUSTS AROUND 20 KT THROUGH THIS EVENING BEFORE EASING AND
BECOMING LIGHT OVERNIGHT. A SIMILAR CLEARING TIME IS EXPECTED
TUESDAY MORNING AROUND 19Z-20Z. MODERATELY HIGH CONFIDENCE.

VICINITY OF KSFO...VFR CIGS WILL TRANSITIONS TO BORDERLINE
IFR/MVFR CIGS AROUND 03Z-04Z THIS EVENING. UNTIL THEN...MODERATE
WEST WINDS AROUND 15 KT WITH OCCASIONALLY GUSTS TO AROUND 20 KT ARE
EXPECTED. WINDS WILL EASE TO 10 KT OR LESS OVERNIGHT. CLEARING IS
ANTICIPATED AROUND 20Z TUESDAY MORNING. MODERATELY HIGH CONFIDENCE.

SFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...MVFR CIGS WILL LOWER TO VFR EARLY
THIS EVENING. WEST TO SOUTHWEST WINDS AROUND 10 KT EXPECTED
THROUGH THE EVENING WITH LIGHTER WINDS ANTICIPATED OVERNIGHT. CIGS
WILL LIFT TO MVFR AROUND 19Z-20Z TUESDAY MORNING BUT ARE NOT
FORECAST TO CLEAR.

&&

.MARINE...AS OF 2:18 PM PDT MONDAY...NORTHWESTERLY WINDS WILL BE
ON THE INCREASE STARTING TOMORROW AS  HIGH PRESSURE BUILDS IN FROM
THE NORTH. THE BIGGEST IMPACT WILL BE  FOR ZONES NORTH OF POINT
REYES WITH GALE FORCE WINDS EXPECTED IN THE  OUTER ZONE BY LATE
TUESDAY AFTERNOON. IN ADDITION...SHORT PERIOD NORTHWESTERLY SWELL
WILL GREATLY BUILD FOR THE NORTHERN OUTER ZONES ALSO BY TUESDAY
NIGHT.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PT ARENA TO PT REYES 10-60 NM FROM 3 AM
             SCA...SF BAY NORTH OF THE BAY BRIDGE UNTIL 3 AM

&&

$$

PUBLIC FORECAST: RWW
AVIATION: CW
MARINE: BELL

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