Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 191130
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
430 AM PDT SUN APR 19 2015

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

&&

.DISCUSSION...EARLY MORNING SATELLITE IMAGERY SHOWED A THIN SLIVER
OF STRATUS HUGGING OR JUST OFFSHORE THE MENDOCINO COAST. NAM12
AND HIGH RESOLUTION MODELS CONTINUE TO SHOW HIGH BOUNDARY LAYER
HUMIDITIES LINGERING OFFSHORE THE MENDO COAST TODAY. THESE MODELS
ALSO INDICATE SOUTHERLY FLOW DEVELOPING LATER THIS MORNING WHICH
WILL LIKELY PUSH STRATUS ONTO THE MENDO COAST. THE LAYER WILL
REMAIN SHALLOW AND CONFINED TO THE IMMEDIATE COAST. IN STARK
CONTRAST...SKIES HAVE BEEN CLEAR NORTH OF THE CAPE THROUGH THE
NIGHT. AN OFFSHORE FLOW HAS PREVENTED SIGNIFICANT STRATUS FROM
REGENERATING. A FEW PATCHES OF FLEETING MIST HAVE BEEN REPORTED BY
THE AUTOMATED WEATHER MACHINES AT THE AIRPORTS. SUSPECT THESE
MISTY AIR CONDITIONS WILL NOT LAST LONG OR BE OF ANY PARTICULAR
SIGNIFICANCE. SOUTHERLY FLOW NEAR SHORE WILL LIKELY DRAW THE
STRATUS NORTHWARD TONIGHT AND THEN ONTO THE REDWOOD COAST BY
MONDAY MORNING. THERE IS A SLIGHT CHANCE FOR DENSE FOG AS
STRATUS ROUNDS THE CAPE TONIGHT. STRONGER ONSHORE FLOW WILL
PROBABLY KEEP THE LOW CLOUDS AND FOG ALONG THE IMMEDIATE
COAST LONGER ON MONDAY.

WATER VAPOR IMAGERY SHOWED AN UPPER LEVEL LOW SW OF CAPE MENDO
SLOWLY DRIFTING TO THE SOUTHWEST. A RIDGE ALOFT FOLDING OVER THE
LOW INTO THE PAC NW WILL SLOWLY SAG SOUTHWARD OVER FAR NORTHERN
CALIFORNIA THROUGH THE DAY TODAY. SOUTHEAST FLOW ALOFT IN THE
700-500MB LAYER WILL DEVELOP IN BETWEEN THESE TWO CENTERS RIGHT
OVER MENDO COUNTY TODAY. THE LATEST RUN OF THE GFS AND NAM12
INDICATE MUCAPE IN EXCESS OF 1000J/KG AND LIFTED INDICES NEAR
-3C ACROSS SW HUMBOLDT...NRN MENDOCINO AND FAR SOUTHERN TRINITY
COUNTIES DURING PEAK HEATING. EVEN WITH THESE IMPRESSIVE
CONVECTIVE PARAMETERS...THE AIR MASS IS STILL DRY WITH THE GFS
PWAT VALUES AROUND 0.70IN AND 700-500MB HUMIDITIES AROUND 40%.
THERE IS STILL THE POSSIBILITY OF MORE LIGHTNING STRIKES THIS
AFTERNOON BUT NOT MUCH IN THE WAY OF PRECIP FROM THE STORMS. THUS
ADDED A SLIGHT CHANCE SOUTH OF ROUTE 36 AND NORTH OF ROUTE 2O.

GOING INTO MONDAY THE NAM12 AND GFS CONTINUE TO INDICATE INSTABILITY
OVER THE INTERIOR FOR MORE SLIGHT CHANCES OF SHOWERS AND THUNDERSTORMS.
PWAT VALUES DO NOT CHANGE MUCH. THE GFS ACTUALLY SHOWS SLIGHTLY
LOWER PWATS ON MONDAY. AN APPROACHING TROUGH ON TUESDAY SHOULD
IMPORT HIGHER PWATS INTO THE AREA AND CREATE STRONGER LARGE SCALE
LIFTING FOR MORE PRODUCTIVE AND SUSTAINED UPDRAFTS. THE GFS AND
ECMWF SHOW THE TROUGH SPLITTING OFFSHORE BEFORE REACHING THE
COAST. MODELS CONTINUE TO INDICATE INSTABILITY LINGERING ON WED
FOR MORE CHANCES OF INTERIOR CONVECTION...PRIMARILY TRIGGERED BY
DAYTIME HEATING.

THE MODELS CONTINUE TO SHOW A RIDGE NOSING TOWARD THE AREA ON
THU AS THE TROUGH ALOFT EDGES EAST AND SOUTHEAST. A SEVERAL MORE
SHORT-WAVE TROUGHS WILL MOVE TOWARD NW CAL THU THROUGH SAT. ONCE
AGAIN ANY PRECIP FROM THESE WAVES WILL LIKELY BE OVER THE
INTERIOR...CONVECTIVE IN NATURE...AND DRIVEN BY THE TERRAIN AND
HEATING OF THE DAY. LATEST GFS INDICATES PARAMETERS FAVORABLE FOR
THUNDERSTORMS ON THU WITH AN APPROACHING SHORT-WAVE. THUS WILL ADD
A SLIGHT CHANCE OF THUNDERSTORMS TO MAINLY TRINITY COUNTY ON THU.
EVEN THOUGH WE HAVE A CHANCE OR SLIGHT OF SHOWERS JUST ABOUT
EVERY DAY AND NIGHT NEXT WEEK...IT WILL BE DRY MOST OF THE TIME
FOR MOST OF THE AREA. THE GFS AND ECMWF SHOW A MORE ORGANIZED AND
CONSOLIDATED TROUGH AFFECTING NW CAL NEXT WEEKEND. THIS FRONT MAY
BRING A DECENT SHOT OF RAIN TO THE AREA LATE NEXT WEEKEND.

&&

.AVIATION...AN UPPER LOW HAS PUSHED OFF THE NORTHWEST CALIFORNIA
COAST PULLING THE THERMAL TROUGH TO THE COAST. THIS HAS ALLOWED
OFFSHORE FLOW TO INTENSIFY NORTH OF CAPE MENDOCINO RESULTING IN
MOSTLY VFR CONDITIONS. SOME LOCAL RADIATION FOG HAS FORMED ALONG THE
COAST RESULTING IN LIFR CONDITIONS...BUT THIS SHOULD BE SHORT LIVED
EARLY THIS MORNING WITH VFR PERSISTING THROUGH THE AFTERNOON. FOG
SOUTH OF CAPE MENDOCINO WILL ATTEMPT TO MOVE BACK NORTH AROUND THE
CAPE LATE THIS AFTERNOON/EVENING BRINGING A RETURN OF IFR OR LIFR
CONDITIONS TONIGHT FOR ACV AND CEC.

VFR WILL PERSIST ACROSS THE INTERIOR ALTHOUGH AN ISOLATED
THUNDERSTORM OR TWO WILL BE POSSIBLE OVER THE HIGHER TERRAIN THIS
AFTERNOON/EVENING. /RPA

&&

.MARINE...THE TIGHTEST PRESSURE GRADIENT WILL PUSH WEST TODAY AS THE
THERMAL TROUGH MOVES OVER THE COAST. THIS WILL ALLOW WINDS TO
DIMINISH AND SEAS TO SUBSIDE TODAY. HOWEVER WITH NEAR SMALL CRAFT
FORCE WINDS JUST NORTH OF THE NORTHERN OUTER WATERS ZONE IT IS
LIKELY THAT STEEP SHORT PERIOD SEAS WILL CONTINUE TO PROPAGATE INTO
THE WESTERN HALF OF THAT ZONE. THUS A SMALL CRAFT ADVISORY HAS BEEN
ISSUED TO COVER THE LOCALLY ELEVATED SEAS. NEAR THE COAST LIGHT
SOUTHERLY WINDS WILL LIKELY DEVELOP TODAY WITH A WEAK AREA OF LOW
PRESSURE LOCATED OFF THE MENDOCINO COAST.

NORTHERLY WINDS AND SEAS WILL RAMP UP AGAIN TUESDAY NIGHT INTO
WEDNESDAY AS AN AREA OF LOW PRESSURE SLIDES DOWN THE WEST COAST.
MODELS REMAIN IN RELATIVELY GOOD AGREEMENT ON THE RAMP UP TIMING AND
THE POTENTIAL FOR STRONG GALE CONDITIONS. THUS...EVEN THOUGH ITS
STILL THREE DAYS OUT...A GALE WATCH HAS BEEN ISSUED FOR THE OUTER
WATER ZONES FOR TUESDAY NIGHT THROUGH WEDNESDAY NIGHT MATCHING WITH
THE OCEAN PREDICTION CENTER. NEAR GALE FORCE WINDS WILL BE LIKELY IN
THE INNER WATERS AS WELL BUT CONFIDENCE IN ANY GALES IN THE INNER
WATERS IS NOT REMOTELY CLOSE ENOUGH TO PINPOINT A WINDOW TO ISSUE A
WATCH AT THIS TIME. /RPA

&&

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

     HAZARDOUS SEAS WARNING UNTIL 3 AM PDT EARLY THIS MORNING FOR
     PZZ450.

     GALE WATCH FROM TUESDAY EVENING THROUGH LATE WEDNESDAY NIGHT FOR
     PZZ470-475.

     SMALL CRAFT ADVISORY UNTIL 9 PM PDT TUESDAY FOR PZZ470.

     GALE WARNING UNTIL 3 AM PDT EARLY THIS MORNING FOR PZZ470.

     SMALL CRAFT ADVISORY UNTIL 3 AM PDT EARLY THIS MORNING FOR
     PZZ455.

     SMALL CRAFT ADVISORY UNTIL 9 AM PDT THIS MORNING FOR PZZ475.

     HAZARDOUS SEAS WARNING UNTIL 3 AM PDT EARLY THIS MORNING FOR
     PZZ475.

&&

$$

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