713
FXUS66 KMTR 021553
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
853 AM PDT THU JUL 2 2020
SYNOPSIS
SEASONAL TEMPERATURES TODAY, FOLLOWED BY
WARMING THROUGH INDEPENDENCE DAY, WITH MINOR DAY TO DAY CHANGES
POSSIBLE NEXT WEEK. LIGHT TO MODERATE ONSHORE FLOW WILL PREVAIL
THROUGH THE PERIOD, ALONG WITH AREAS OF NIGHT AND MORNING COASTAL
LOW CLOUDS AND FOG.
DISCUSSION...AS OF 8:50 AM PDT THURSDAY
THE MARINE LAYER IS
EVIDENT ON VISIBLE SATELLITE IMAGERY THIS MORNING ALONG THE COAST
AND THE INLAND VALLEYS. THE BODEGA BAY PROFILER SUGGESTS A DEPTH
OF AROUND 2000 FEET WHILE THE FORT ORD PROFILER IS CLOSER TO 2500
FEET THIS MORNING. NORTHWEST WINDS AND A DRIER AIR MASS ROUNDING
CAPE MENDOCINO HAVE SCOURED OUT A HOLE IN THE MARINE LAYER FARTHER
OFFSHORE BUT NO HOLES EXIST IN THE STRATUS ALONG THE IMMEDIATE
COAST. A SURFACE EDDY IS DRIVING WEAK SOUTHWEST WINDS AND HELPING
TO REINFORCE THE MARINE LAYER INLAND FROM THE THICKER LAYER TO THE
SOUTH RATHER THAN THE DRIER AIR FROM THE NORTHWEST. AS SUCH,
COULD SEE THE LOW CLOUDS LINGER THROUGH THE MID TO LATE MORNING
FOR MARINE INFLUENCED SITES. NO SIGNIFICANT CONCERNS TODAY WITH
SOMEWHAT BELOW NORMAL TEMPERATURES (3-11 DEGREES) ACROSS THE
REGION.
HIGH PRESSURE BUILDS FROM THE DESERT SOUTHWEST OVER THE NEXT FEW
DAYS AND WILL BRING A WARMING/DRYING TREND WHICH WILL PEAK ON
SATURDAY (INDEPENDENCE DAY). TEMPERATURES WILL RISE TO BECOME
SLIGHTLY TO SOMEWHAT ABOVE SEASONABLE CONDITIONS, MAINLY INLAND,
WHERE AFTERNOON HIGHS WILL BE IN THE MID 80S TO MID 90S, MEANWHILE
(SAN JOSE, CONCORD, LIVERMORE, SANTA ROSA, NAPA), THE SAN
FRANCISCO BAY/MONTEREY BAY SHORELINES WILL BE IN THE LOW 70S TO
LOW 80S. A PERIOD OF NORTH TO NORTHWEST WINDS SATURDAY NIGHT INTO
SUNDAY MORNING WILL EXACERBATE FIRE WEATHER RISK FOR THE NORTH
BAY HILLS AND MOUNTAINS. MEANWHILE, LOW HUMIDITY VALUES WILL
ELEVATE FIRE WEATHER RISK GIVEN THE INCREASE IN THE NUMBER OF FIRE
WORKS BEING SHOT OFF THIS WEEKEND, ESPECIALLY GIVEN THAT THE LOCAL
WRF SUGGESTS A COMPRESSION AND SIGNIFICANT WEAKENING OF THE MARINE
LAYER BY SATURDAY NIGHT. THAT SAID, THE MAIN FIRE RISK WILL BE
FROM HUMAN RELATED ACTIVITIES THROUGH THE HOLIDAY WEEKEND (RATHER
THAN FROM THE WEATHER CONDITIONS) SO PLEASE BE MINDFUL OF ANY
OUTDOOR ACTIVITIES THAT MAY LEAD TO A SPARK THAT COULD IGNITE A
WILDFIRE.
NO UPDATES PLANNED THIS MORNING. SEE PREVIOUS DISCUSSION FOR MORE
DETAILS ON THE CURRENT FORECAST.
PREVIOUS DISCUSSION...AS OF 3:15 AM PDT THURSDAY
A
RETROGRADING UPPER LEVEL LOW OVER THE PACNW AND BROAD UPPER TROUGH
COVERING MUCH OF THE WEST COAST CONTINUES TO BE THE LARGE SCALE
WEATHER FEATURES OF NOTE. THE LOWERING 500 MB HEIGHTS, DECREASING
N-S GRADIENT AND CONTINUED ONSHORE FLOW ALLOWED FOR A BETTER
MARINE LAYER PUSH OVERNIGHT. SATELLITE FOG PRODUCT SHOWS SOLID
STRATUS ALONG THE ENTIRE COASTLINE, UP THE SALINAS VALLEY, IN SAN
FRANCISCO BAY AND EVEN IN THE NORTH BAY VALLEYS. FORT ORD PROFILER
PUTS THE DEPTH AT NEAR 2,000 FEET. THE DEEPER MARINE LAYER HAS
REDUCED CHANCES FOR DENSE FOG, BUT PATCHY FOG AND SOME COASTAL
DRIZZLE ARE STILL POSSIBLE EARLY THIS MORNING. TODAY'S WEATHER
WILL BE SIMILAR TO WEDNESDAY WITH INLAND SUNSHINE AND COASTAL
CLOUDS. TEMPERATURES WILL BE WITH IN A FEW DEGREES OF YESTERDAY OR
60/70S COAST AND 80/90S INTERIOR.
THE CURRENT FORECAST FOR FRIDAY AND THE UPCOMING HOLIDAY WEEKEND
REMAIN ON TRACK. THE UPPER TROUGH BEGINS TO LIFT NORTHWARD ON
FRIDAY AS A RIDGE OF HIGH PRESSURE BUILDS IN FROM THE DESERT
SOUTHWARD. FRIDAY WILL FEATURE A SLIGHT UPWARD TREND IN
TEMPERATURES, BUT MORE NOTICEABLE WARMING WILL OCCUR OVER THE
HOLIDAY WEEKEND. NO MAJOR HEAT RISK CONCERNS WITH THE WARM UP, BUT
TEMPERATURES AWAY FROM THE COAST WILL BE ABOVE SEASONAL AVERAGES.
LACK OF STRONG OFFSHORE FLOW OR STRONG NORTHERLY GRADIENTS WILL
KEEP NIGHT/MORNING LOW CLOUDS IN THE FORECAST AS WELL.
ONE POTENTIAL ITEM OF CONCERN FOR THE UPCOMING HOLIDAY WEEKEND
WILL BE A VERY DRY AIRMASS MOVING IN OVER THE REGION SATURDAY
NIGHT/EARLY SUNDAY MORNING. LASTEST LOCAL WRF MODEL DEVELOPS WEAK
OFFSHORE FLOW AT 2500 FEET WITH LOWERING HUMIDITY 25-35% OVER
HIGHER TERRAIN. FORTUNATELY, WINDS DO NOT APPEAR TO OVERLY STRONG
SATURDAY NIGHT. NONETHELESS, DRY AND MILD CONDITIONS IN THE HILLS
COMBINE WITH POSSIBLE FIREWORKS WILL HEIGHTEN FIRE WEATHER
CONCERNS.
HIGH PRESSURE RETREATS SOUTHWARD ON MONDAY AS ANOTHER TROUGH
APPROACHES FROM THE NW. A SLIGHT COOLING TREND DEVELOPS EARLY NEXT
WEEK. THE LATEST MEDIUM RANGE MODELS KEEP COOLING TREND FOR MUCH
OF NEXT WEEK WITH NIGHT/MORNING CLOUDS.
AVIATION...AS OF 04:28 AM PDT THURSDAY
FOR 12Z TAFS. SATELLITE
IMAGERY SHOWS STRATUS REMAINS ALONG THE COAST WITH PATCHY LOW
CLOUDS AROUND THE SF BAY AREA AND OVER THE MONTEREY BAY. PATCHY
MVFR/IFR CIGS THIS MORNING ALONG THE COAST AND AROUND THE SF BAY
THROUGH ABOUT 16Z-17Z WITH LATER CLEARING TIMES AROUND THE
MONTEREY BAY. SOUTHERLY WINDS ANTICIPATED TO KEEP STRATUS OUT OF
SJC. S/SW WINDS THIS MORNING AROUND TURNING W/SW THIS AFTERNOON
AROUND 10-15 KT WITH LOCALLY HIGHER GUSTS POSSIBLE. EXPECTING
STRATUS TO RETURN TONIGHT.
VICINITY OF KSFO...SOUTHERLY WINDS MAY KEEP CIGS FROM BECOMING BKN
AROUND THE TERMINAL, THOUGH MVFR CONDITIONS POSSIBLE THROUGH
ABOUT 16Z-17Z THIS MORNING. LIGHT SOUTHERLY WINDS THIS MORNING
BECOMING WESTERLY THIS AFTERNOON AROUND 15 KT.
SFO BRIDGE APPROACH...SIMILAR TO KSFO, THOUGH CLOUDS MAY FILL IN
OVER THE APPROACH WHILE SOUTHERLY WINDS KEEP THE TERMINAL CLEAR.
MONTEREY BAY TERMINALS...MVFR/IFR CIGS THROUGH ABOUT 18Z-20Z. IT
IS POSSIBLE FOR KMRY TO REMAIN UNDER BKN CONDITIONS ALL DAY,
THOUGH CONFIDENCE IS LOW. SHOULD CLEARING OCCUR, EXPECT AN EARLY
RETURN LATE THIS AFTERNOON/EARLY THIS EVENING. LIGHT WINDS THIS
MORNING BECOMING ONSHORE THIS AFTERNOON AROUND 10-15 KT.
MARINE...AS OF 08:34 AM PDT THURSDAY
MODERATE TO STRONG
NORTHWEST WINDS WILL CONTINUE OVER THE NORTHERN OUTER WATERS
TODAY. THESE WINDS WILL GENERATE STEEP FRESH SWELL RESULTING IN
HAZARDOUS SEAS CONDITIONS, PARTICULARLY FOR SMALLER VESSELS.
GENERALLY LIGHT TO MODERATE WINDS EXPECTED ELSEWHERE AS HIGH
PRESSURE WEAKENS OFF THE CALIFORNIA COAST AND A LOW PRESSURE
SYSTEM DEVELOPS OFF THE PACIFIC NORTHWEST. WINDS WILL BEGIN TO
SUBSIDE TONIGHT AND TOMORROW, THOUGH LOCALLY BREEZY CONDITIONS
OVER THE NORTHERN OUTER WATERS WILL PERSIST INTO THE WEEKEND. A
LONG-PERIOD SOUTHERLY SWELL TRAIN WILL ARRIVE LATE TONIGHT INTO
TOMORROW. THIS WILL CAUSE OCCASIONAL BREAKING WAVES OVER
NEARSHORE SHOALS AND STRONG CURRENTS ALONG THE COAST, ESPECIALLY
NEAR POINTS AND HEADLANDS.
MTR WATCHES/WARNINGS/ADVISORIES
.TDAY...SCA...PT ARENA TO PIGEON PT 10-60 NM
SCA...SF BAY UNTIL 9 AM
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 9 AM
SCA...SF BAY FROM 3 PM
PUBLIC FORECAST: DRP/MM
AVIATION: AS
MARINE: AS/STR
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