143
FXUS66 KMTR 131209
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
409 AM PST FRI DEC 13 2019
SYNOPSIS
AREAS OF DENSE FOG WILL PREVAIL ACROSS THE COAST AND
THE COASTAL VALLEYS THIS MORNING, WITH A DISTURBANCE SPREADING
LIGHT RAIN ACROSS THE REGION LATER TODAY AND TONIGHT. THE THREAT
OF LIGHT RAIN WILL CONTINUE INTO THIS WEEKEND, AS A COLD FRONT
TAKES AIM AT NORTHERN CALIFORNIA. DRIER AND COLDER CONDITIONS
WILL PREVAIL ON SUNDAY, WITH FROST POSSIBLE SUNDAY NIGHT. AN
UNSETTLED AND WET PATTERN WILL LIKELY TO RETURN BY THE MIDDLE OF
NEXT WEEK.
DISCUSSION...AS OF 03:55 AM PST FRIDAY
WATER VAPOR IMAGERY
SHOWS A DIRTY RIDGE OVER NORTHERN CALIFORNIA THIS MORNING, WITH
PLENTY OF HIGH CLOUD COVER SPREADING ACROSS THE NORTH BAY. THUS
FAR, THIS HIGH CLOUD COVER IS NOT IMPEDING FOG DEVELOPMENT ACROSS
THE NORTH BAY, AS ALL OF OUR NORTH BAY SITES ARE CURRENTLY
REPORTING VISIBILITY AT OR BELOW A QUARTER MILE. FARTHER SOUTH,
COASTAL AREAS AND THE COASTAL VALLEYS ARE ALSO DEALING WITH THIS
DENSE FOG, INCLUDING SFO. THIS DENSE FOG WILL MAKE FOR A NASTY
MORNING COMMUTE, WITH DELAYS POSSIBLE MOST OF OUR AIRPORTS.
THEREFORE, A DENSE FOG ADVISORY REMAINS IN EFFECT THIS MORNING
THROUGH 8 AM FOR ALL COASTAL REGIONS AND VALLEYS.
LIGHT RAIN WILL ALSO GRADUALLY SPREAD ACROSS THE REGION TODAY, AS
THE NEXT SYSTEM TAKES AIM AT NORTHERN CALIFORNIA. IN FACT, RADAR
IS PICKING UP ON SOME LIGHT RETURNS ACROSS NORTHERN SONOMA ALREADY,
WITH A FEW SITES REPORTING A HUNDREDTH HERE AND THERE. THE NORTH
HALF OF THE BAY AREA WILL LIKELY SEE THE BRUNT OF THE RAIN OVER
THE NEXT 24 HOURS, BUT AMOUNTS WILL REMAIN LIGHT FOR THE MOST. A
COLD FRONT WILL THEN MOVE ACROSS THE REGION LATE IN THE DAY ON
SATURDAY. ALTHOUGH THIS COLD FRONT WILL BRING SOME LIGHT RAIN TO
THE REGION, THE BIGGEST IMPACT WILL BE WITH THE COLDER AND DRIER
AIR MOVING IN BEHIND THE FRONT. ALTHOUGH SUNDAY WILL BE SLIGHTLY
COOLER THAN SATURDAY, THE MAIN IMPACT WILL BE ON THE OVERNIGHT
TEMPERATURES SUNDAY NIGHT. IN FACT, FROSTY CONDITIONS WILL BE
POSSIBLE, AS TEMPERATURES FALL INTO THE LOWER TO MID 30S ACROSS
THE INLAND VALLEYS.
DRIER AND WARMER CONDITIONS WILL GRADUALLY DEVELOP FOR THE FIRST
PART OF THE WORK WEEK, AS HIGH PRESSURE BUILDS OVER THE WEST
COAST. HOWEVER, MODELS CONTINUE TO HINT THAT A WET AND UNSETTLED
PATTERN WILL RETURN FOR THE LATTER PART OF THE WORK WEEK. AT THIS
POINT IN TIME, THERE ARE STILL SOME SIGNIFICANT MODEL DIFFERENCES
IN THE TIMING AND STRENGTH, BUT BELIEVE A MORE PROGRESSIVE
PATTERN IS LIKELY LOOKING TO THE ENSEMBLES. PALMER
AVIATION...AS OF 04:08 AM PST FRIDAY
LIFR CONDITIONS ARE
CURRENTLY IMPACTING MOST TERMINALS ACROSS THE SAN FRANCISCO BAY
AREA AND MONTEREY BAY REGION WITH IFR CEILINGS OVER INTERIOR EAST
BAY TERMINALS. LOW CLOUDS AND AREAS OF DENSE FOG WILL PERSIST
THROUGH ABOUT 15Z WITH IMPROVING CONDITIONS LIKELY AFTER 18Z.
HOWEVER, LOW CEILINGS WILL LIKELY KEEP MVFR TO IFR CONDITIONS
THROUGH MUCH OF THE DAY. A WEAK FRONTAL SYSTEM WILL THEN DROP
SOUTHWARD ACROSS THE REGION RESULTING IN LIGHT RAIN DEVELOPING
AROUND 21Z OVER THE NORTH BAY, 00Z ACROSS THE BAY AREA AND THEN
03Z FOR THE MONTEREY BAY REGION. PERIODS OF LOWERING VISIBILITY
AND CEILINGS WILL ALSO BE POSSIBLE DURING TIMES OF HEAVIER
PRECIPITATION. PRECIPITATION SHOULD DIMINISH REGION-WIDE BY 06Z,
YET WORSENING FLIGHT CONDITIONS ARE AGAIN LIKELY TO DEVELOP
OVERNIGHT THROUGH SATURDAY MORNING DUE TO RESIDUAL MOISTURE AND
LIGHT WINDS IN PLACE.
VICINITY OF KSFO...PATCHY DENSE FOG OVER THE TERMINAL WILL RESULT
IN LIFR CONDITIONS THROUGH EARLY MORNING WITH THE POTENTIAL
IMPROVING VISIBILITIES AND CEILINGS AROUND 15Z AND MORE SO BY 18Z.
MVFR CONDITIONS ARE THEN LIKELY THROUGH MUCH OF THE REMAINDER OF
THE DAY WITH LIGHT RAIN LIKELY TO DEVELOP AFTER 21Z. GENERALLY
LIGHT AND VARIABLE WINDS ARE LIKELY THROUGH THIS EVENING WITH AN
INCREASE IN WEST-NORTHWEST WINDS LATE IN THE PERIOD.
SFO BRIDGE APPROACH...SIMILAR TO KSFO.
MONTEREY BAY TERMINALS...LIFR CONDITIONS IMPACTING REGIONAL
TERMINALS WITH PATCHY DENSE FOG AND LOW CEILINGS. LIGHT WINDS ALSO
PERSIST AND WILL LIKELY CONTINUE THROUGH MUCH OF THE DAY.
CONDITIONS SHOULD IMPROVE AFTER 18Z TO IFR/MVFR WITH THE POTENTIAL
FOR LIGHT RAIN TO DEVELOP AROUND 03Z.
MARINE...AS OF 04:08 AM PST FRIDAY
SOUTHERLY WINDS WILL
PERSIST TODAY AHEAD OF A WEAK FRONTAL BOUNDARY APPROACHING THE
REGION. WINDS WILL SWITCH TO THE NORTHWEST TONIGHT AND INCREASE ON
SATURDAY AS A COOL UPPER LEVEL TROUGH PASSES TO THE NORTH OF THE
AREA. LARGE LONG-PERIOD NORTHWEST SWELL WILL IMPACT THE WATERS
THROUGH SATURDAY.
MTR WATCHES/WARNINGS/ADVISORIES
.TDAY...DENSE FOG ADVISORY...CAZ006-505-506-509-528>530
HIGH SURF ADVISORY...CAZ006-505-509-529-530
SCA...PT ARENA TO PT REYES 0-10 NM
SCA...PT REYES TO PIGEON PT 0-10 NM
SCA...PIGEON PT TO PT PINOS 0-10 NM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
SCA...PT ARENA TO PIGEON PT 10-60 NM
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
PUBLIC FORECAST: PALMER
AVIATION: RGASS
MARINE: RGASS
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