Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 142234
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
334 PM PDT SUN SEP 14 2014

.SYNOPSIS...A SHALLOW MARINE WILL SLOWLY DEEPEN OVER THE NEXT
COUPLE OF DAYS AS AN UPPER LEVEL RIDGE MOVES AWAY TO THE EAST.
AN UPPER LEVEL TROUGH WILL SLOWLY APPROACH THE AREA FROM THE
WEST EARLY THIS WEEK BRINGING A CHANCE OF SHOWERS AROUND MID
WEEK.

&&

.DISCUSSION...MARINE LAYER DEEPENED SLIGHTLY TODAY AS A SHORT-WAVE
TROUGH APPROACHED 130W. AS A RESULT...LOW CLOUDS HAVE BEEN HANGING
AROUND THE COAST LONGER TODAY. THE LAYER WILL LIKELY CONTINUE TO
INCREASE TONIGHT INTO MONDAY AND PUSH A LITTLE FARTHER INTO THE
COASTAL RIVER VALLEYS AS THE SHORT-WAVE TROUGH APPROACHES.

THE APPROACHING SHORT-WAVE TROUGH WILL CREATE SLIGHT INSTABILITY
ON MONDAY. HOWEVER THIS TROUGH IS DRY AND EXPECT ONLY TOWERING
CUMULUS OVER THE MOUNTAINS AGAIN. NEW 12Z MODELS CONTINUE TO
INDICATE WEAK SURFACE BASED INSTABILITY AROUND THE PERIPHERY OF
DEL NORTE AND TRINITY COUNTIES AS ROBUST SOUTHWESTERLY FLOW ALOFT
DEVELOPS. THE TOWERING CU THAT DO DEVELOP WITH DAYTIME HEATING
WILL QUICKLY MOVE OFF TO THE NE INTO SISKIYOU COUNTY. THE SHORT-
WAVE WILL EXIT TO THE NORTHEAST BY MONDAY EVENING. WE SHOULD SEE
A BETTER MARINE PUSH BEHIND IT MON NIGHT INTO TUE MORNING. MARINE
CLOUD COVER AND RH`S WILL INCREASE BY TUE AS DEEPER AND STRONGER
SW FLOW ALOFT DEVELOPS. PRECIP CHANCES SEEM VERY MARGINAL ON TUE
AND FOR NOW WILL KEEP THE FORECAST DRY WITH ONLY 5-10% CHANCES.

INLAND TEMPERATURES WERE A LITTLE COOLER AT SOME LOCATIONS BUT
WARMER OR ABOUT THE SAME AT OTHERS. 850MB TEMPERATURES DECREASE
SOME ON MONDAY...BUT NOT VERY MUCH. MODIFIED MARINE AIR SHOULD
CONTINUE TO FILTER INTO THE COASTAL RIVER VALLEYS ON MONDAY AND
PROVIDE FOR SOME COOLING. EVEN INTO TUE...THE 85OMB COOLING DOES
NOT LOOK TO BE ALL THAT GREAT. ANY COOLING ON TUE WILL BE DUE TO
MARINE AIR. LARGER SCALE COOLING WILL PROBABLY HOLD OFF TIL WED OR
THU AS A LARGER AND STRONGER SHORT-WAVE TROUGH MOVES TOWARD THE
REGION. THIS TROUGH WILL BRING A CHANCE OF SHOWERS ON WED AND THU.
THE NAM12...GFS AND ECMWF ALL HAVE PRECIP COMING IN WED AFTERNOON.
THERE IS STILL UNCERTAINTY ON THE TIMING AND AMOUNTS OF RAIN...BUT
WE INCREASED PRECIP CHANCES SLIGHTLY IN ALL ZONES ON WED. SLIGHT
INSTABILITY ASSOCIATED WITH SWLY SPEED MAX MAY ENHANCE THE PRECIP
PRODUCTION WITH PERHAPS A TENTH OR TWO OF RAIN AROUND CAPE MENDO
AND OVER THE KING RANGE. THE MODELS DIFFER ON HOW THE TROUGH WILL
EVOLVE ON THU AS THE WHOLE SYSTEM SPLITS APART. IT STILL LOOKS
LIKE THERE WILL BE MOISTURE AND INSTABILITY ON THU FOR SOME
SHOWERS. I AM NOT CONVINCED ON THE TIMING THE GFS AND ECMWF SHOW.
THE UPPER LOW MAY TAKE LONGER TO EXIT THE REGION. FOR NOW WILL
MAINTAIN SILENT PRECIP CHANCES INTO THU NIGHT. BOTH 12Z SOLUTIONS
CONTINUE WITH PREVIOUS TRENDS OF A RIDGE BUILDING OVER THE AREA
FRI AND SAT. THIS SHOULD BRING WARMING AND DRYING TO INTERIOR. THE
NEW RUN OF THE GFS HAS WEAKER OFFSHORE NOW...SO COASTAL AREAS MAY
END UP SEEING MORNING CLOUDS AND PERHAPS SOME FOG NEXT WEEKEND.

&&

.AVIATION....STRATUS CONTINUES TO HUG THE COASTLINE WITH LIFR
CONDITIONS AT COASTAL TERMINALS. ANOTHER NIGHT OF LIFR WITH
VISIBILITIES AND CEILINGS POSSIBLY FALLING BELOW TERMINAL MINIMUMS
TONIGHT BEFORE CEILINGS BEGIN TO LIFT ON MONDAY AHEAD OF AN
APPROACHING UPPER LEVEL SYSTEM. VFR WILL CONTINUE TO PREVAIL
ACROSS THE INTERIOR...THOUGH SOME STRATUS MAY TRY TO PUSH INTO
SOUTHERN MENDOCINO COUNTY TONIGHT AROUND HOPLAND. RPA

&&

.MARINE...HIGH PRESSURE WILL BEGIN TO BREAK DOWN TONIGHT INTO MONDAY
ALLOWING WINDS TO TURN OUT OF THE SOUTH AS A LOW PRESSURE SYSTEM
MOVES TOWARD THE COASTLINE. MODELS CONTINUE TO INDICATE THAT THE
SURFACE LOW WILL REMAIN OFF THE COAST THROUGH WEDNESDAY AND THEN
WEAKEN AS IT APPROACHES THE COAST. SOME SOUTHERLY GUSTS TO AROUND 25
KT WILL BE POSSIBLE ON WEDNESDAY OVER THE OUTER WATERS WHEN THE
PRESSURE GRADIENT IS TIGHTEST. AT THIS TIME NO SMALL CRAFT
ADVISORIES ARE ANTICIPATED.

THE SURFACE LOW WILL WEAKEN ON THURSDAY AS THE PARENT UPPER LEVEL
TROUGH MOVES INLAND. THIS WILL ALLOW LOWER PRESSURE TO DEVELOP
OVER THE INTERIOR AND NORTHERLY WINDS TO INCREASE OVER THE WATERS.
SOME SMALL CRAFT FORCE NORTHERLY WINDS WILL BE POSSIBLE FRIDAY
INTO THE WEEKEND OVER THE OUTER WATERS.

A SOUTHWESTERLY LONG PERIOD SWELL IS STILL ANTICIPATED TO MOVE INTO
THE WATERS IN THE NEXT 24 HOURS OR SO. WHAT WAS THOUGHT AS A SWELL
COMING IN SMALLER THAN PREDICTED IN HAWAII WAS ACTUALLY JUST A
DELAYED DEVELOPMENT OF THE SWELL. THUS SWELL HEIGHTS ARE NOW
ANTICIPATED TO REACH AROUND 3 FEET AT AROUND 20 SECONDS TUESDAY INTO
WEDNESDAY. THIS WILL RESULT IN SOME HIGHER WAVE ACTION THAN
NORMAL ON SOUTH FACING BEACHES. RPA

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...NONE.
&&

$$

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