Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 181205
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
457 AM PDT SAT APR 18 2015

.SYNOPSIS...HIGH PRESSURE OVER THE WEST COAST WILL MAINTAIN WARM
WEATHER ACROSS THE INTERIOR THROUGH THE WEEKEND. THE COAST CAN
EXPECT LOW CLOUDS...MAINLY DURING THE NIGHT AND MORNING HOURS.

&&

.DISCUSSION...EARLY MORNING SATELLITE IMAGERY SHOWED STRATUS
ALONG MOST OF THE COAST. THE STRATUS WILL LIKELY SCATTER OUT
BY THIS AFTERNOON...HOWEVER REDEVELOPMENT WILL OCCUR BY MID TO
LATE AFTERNOON AS NORTHERLY FLOW TRANSPORTS HIGH HUMIDITY AIR ONTO
THE COAST. NAM12 AND HIGH RESOLUTION MODELS CONTINUE TO INDICATE
SUBSTANTIAL BOUNDARY LAYER DRYING TONIGHT INTO SUNDAY IN RESPONSE
TO AN EASTERLY PUSH OF DRY AIR. WITH A STRONG MARINE INVERSION
PRESENT FIND IT HARD TO BELIEVE THE EASTERLY WINDS WILL TRANSLATE
DOWN TO MEAN SEA LEVEL AND COMPLETELY ERADICATE THE STRATUS AND
FOG. FOR NOW MAINTAINED PATCHY FOG ALONG THE COAST...BUT REDUCED SKY
COVER ALONG THE REDWOOD COAST WHERE THE STRATUS SHOULD CLEAR OUT
RAPIDLY SUNDAY. DEVELOPING SOUTHERLY FLOW SOUTH OF THE CAPE ON
SUNDAY MAY KEEP THE STRATUS AND FOG LOCKED ONTO THE IMMEDIATE COAST
ALL DAY. THE STRATUS AND FOG WILL RETURN SUNDAY NIGHT AND MONDAY
ALONG THE ENTIRE COAST AS A STRONGER ONSHORE FLOW PATTERN DEVELOPS
AND AN UPPER TROUGH BEGINS TO APPROACH THE COAST.

IT WILL CONTINUE TO BE SUNNY WITH ABOVE NORMAL TEMPERATURES IN
THE INTERIOR THROUGH THE WEEKEND. THERE IS STILL A SLIGHT CHANCE
OF THUNDERSTORMS THIS AFTERNOON IN THE INTERIOR. VAPOR IMAGERY
SHOWED A DRY SHORT-WAVE DROPPING DOWN FROM THE NORTH EARLY THIS
MORNING. THIS UPPER LEVEL FEATURE WILL DRIFT SOUTHWEST TO JUST
OFFSHORE THE MENDO COAST THIS AFTERNOON. NAM12 AND GFS CONTINUE TO
INDICATE INSTABILITY (LIFTED INDICES AROUND -3C) AND MUCAPE ON
THE ORDER OF 1000J/KG DURING PEAK HEATING. CONFIDENCE IS NOT HIGH
WE ARE GOING TO SEE ANYTHING MORE THAN JUST A FEW CLOUD BUILDUPS.
THE AIR MASS IS TOO DRY FOR STORMS. DRY AIR ENTRAINMENT INTO THE
TOWERING CUMULUS WILL KILL THE UPDRAFTS.

THE MODELS WERE IN DECENT AGREEMENT SHOWING UPPER LEVEL RIDGING
SAGGING SOUTHWARD OVER THE AREA ON SUNDAY. THE GFS CONTINUES TO
INDICATE WEAK INSTABILITY ACROSS EASTERN MENDO COUNTY. WITH NO
MOISTURE TRANSPORT COUPLED WITH THE SOUTHWARD DRIFT OF THE UPPER
LOW THROUGH THE DAY...THE POSSIBILITY FOR ISOLATED CONVECTION IS
LOOKING QUITE BLEAK. EVEN ON MONDAY THE MODELS MAINTAIN A RIDGE
OVER THE AREA WITH NO SUBSTANTIAL MOISTURE TRANSPORT INTO THE
AREA. THE CHANCES FOR CONVECTION ARE NOT LOOKING SO HOT ON MONDAY
EITHER.

THE GFS AND ECMWF INDICATE A SPLITTING UPPER TROUGH APPROACHING
THE WEST COAST ON TUE. THE GFS CONTINUES TO INDICATE CONVECTIVE
PRECIP SPARKING UP WITH THE HEATING OF THE DAY OVER THE INTERIOR
ON TUE. CONVECTIVE PARAMETER ARE FAVORABLE FOR ISOLATED
THUNDERSTORMS. THUS HAVE ADDED THEM TO THE FORECAST. THE UPPER
TROUGH MEANDERS OVER OR NEARBY NORTHERN CALIFORNIA INTO WED AND A
BROAD BRUSH CHANCE OF SHOWERS WITH A SLIGHT CHANCE OF
THUNDERSTORMS HAS BEEN CARRIED INTO WED.

THE MODELS PART COMPANY SIGNIFICANTLY ON THU AND FRI. THE ECMWF
WAS THE MOST AGGRESSIVE WITH DRIVING AN UPPER TROUGH AND PRECIP
TOWARD THE NORCAL COAST BY FRI. THE GFS WAS MUCH DRIER AND HAS A
MEAN RIDGE BUILDING WITH MOSTLY DRY WEATHER ON THU. IF THE ECMWF
PANS OUT...TEMPERATURES WILL BE DRASTICALLY COOLER IN THE INTERIOR
(HIGH IN THE LOWER 60S). THE GFS INDICATES COOLING AS WELL...BUT
NOT TO THE DEGREE OF THE ECMWF. I LEANED TOWARD THE LESS DRASTIC
AND WARMER GFS SCENARIO BUT MAINTAINED NEAR CLIMO PRECIP CHANCES.

&&

.AVIATION...AN UPPER LEVEL RIDGE IS COMPRESSING THE STRATUS ALONG
THE COAST RESULTING IN LOWER CEILINGS THIS MORNING. THERE IS
POTENTIAL FOR A FEW HOURS OF QUARTER MILE VISIBILITY BEFORE MIXING
INCREASES LATER THIS MORNING AND CEILINGS LIFT AGAIN AND EVENTUALLY
MIX OUT RESULTING IN VFR LATE THIS AFTERNOON. STRATUS/FOG WILL
REDEVELOP THIS EVENING. AN AREA OF LOW PRESSURE ALOFT WILL MOVE OVER
THE COAST TONIGHT ALLOWING OFFSHORE FLOW TO INTENSIFY...POSSIBLY
PULLING STRATUS OFF THE COAST AFTER MIDNIGHT ALONG THE HUMBOLDT AND
DEL NORTE COASTS.

VFR WILL PREVAIL ACROSS THE INTERIOR TODAY AND TONIGHT. AN ISOLATED
THUNDERSTORM OR TWO WILL BE POSSIBLE IN THE MOUNTAINS THIS
AFTERNOON/EVENING. /RPA

&&

.MARINE...NORTHERLY WINDS WILL PERSIST TODAY WITH GALE FORCE GUSTS
IN THE NORTHERN OUTER WATERS. THESE WINDS WILL ALLOW SHORT PERIOD
STEEP SEAS TO PROPAGATE INTO THE OTHER ZONES. BUOYS CONTINUE TO
REPORT SEAS OVER 12 FEET...AND SEAS SHOULD ONLY BE LARGER OUTSIDE OF
20 NM. THUS A HAZARDOUS SEAS WARNING HAS BEEN ISSUED FOR THE
SOUTHERN OUTER WATERS ZONE THROUGH EARLY SUNDAY MORNING. WINDS AND
SEAS WILL DECLINE TONIGHT THROUGH SUNDAY AS AN UPPER LOW DEVELOPS
OFF THE NORTHWEST CALIFORNIA COAST. THIS LOW WILL HAVE A SURFACE
REFLECTION WHICH SHOULD PUSH THE STRONGEST PRESSURE GRADIENT WEST
AND ALLOW LIGHT SOUTHERLIES TO DEVELOP NEAR THE COAST. THUS ALL
HEADLINES FALL EARLY SUNDAY MORNING...THOUGH SEAS MAY STILL BE IN
SMALL CRAFT CRITERIA IN THE WESTERN PORTION OF THE OUTER WATER ZONES
AND PRODUCTS MAY NEED TO BE EXTENDED FOR A 12 HOUR PERIOD OR SO.

WINDS WILL BE RELATIVELY LIGHT SUNDAY THROUGH MONDAY WITH THE
THERMAL TROUGH OFF THE COAST. HOWEVER THESE LIGHT WINDS WILL BE
RATHER SHORT LIVED WITH ANOTHER SURGE IN NORTHERLY WINDS EXPECTED BY
MID WEEK. THERE IS GENERAL MODEL AGREEMENT OF NEAR GALE OR GALE
CONDITIONS DEVELOPING BY WEDNESDAY AND CONTINUING THROUGH THE END OF
THE WORK WEEK. IT IS LIKELY THAT GALE WATCHES WILL BE NEEDED IN A
FEW DAYS. /RPA

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY UNTIL 3 AM PDT SUNDAY FOR PZZ450.

     GALE WARNING UNTIL 3 AM PDT SUNDAY FOR PZZ470.

     SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR PZZ455.

     SMALL CRAFT ADVISORY UNTIL 3 AM PDT SUNDAY FOR PZZ475.

     HAZARDOUS SEAS WARNING UNTIL 3 AM PDT SUNDAY FOR PZZ475.

&&

$$

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