Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 282315
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
315 PM PST FRI NOV 28 2014

.SYNOPSIS...ANOTHER FRONTAL SYSTEM WILL BRING MORE RAIN TO NORTHWEST
CALIFORNIA TONIGHT THROUGH SATURDAY. WET AND UNSETTLED WEATHER
CONDITIONS WILL CONTINUE INTO MID NEXT WEEK AS A LOW PRESSURE
SYSTEM SLOWLY BURROWS TOWARD THE CALIFORNIA COAST.

&&

.DISCUSSION...A NARROW BAND OF RAIN MOVED THROUGH THE FORECAST AREA
TODAY...BRINGING LIGHT TO MODERATE RAINFALL. A FEW MOUNTAIN SPOTS
RECEIVED AN INCH OR SO...WHILE MOST LOWER ELEVATION SITES SAW A
FEW TENTHS TO AS MUCH AS 3/4 OF AN INCH IN DEL NORTE. THE RAIN
BAND WILL CONTINUE TO PRODUCE MODERATE RAINFALL SOUTH OF THE CAPE
THIS AFTERNOON INTO EARLY THIS EVENING. THE RAIN WITH THIS FIRST
BAND SHOULD TAPER OFF LATER THIS EVENING IN THE MENDO ZONES.
ANOTHER...POTENTIALLY STRONGER FRONT WILL SAG DOWN FROM THE NORTH
LATE TONIGHT AND BRING MORE RAIN TO THE AREA...MAINLY NORTH OF
CAPE MENDO. THIS NEXT FRONT LOOKS TO BE STRONGER AND SHOULD
PRODUCE SLIGHTLY HIGHER AMOUNTS OF RAIN NORTH OF CAPE MENDOCINO ON
SATURDAY AS THE FRONT SLOWS DOWN OR STALLS NEAR CAPE MENDO. THE
FRONT SHOULD TRANSITION INTO WARM FRONT SAT NIGHT INTO SUN.

A COOLER AIR MASS WILL SETTLE INTO THE PAC NW ON SAT BEHIND
THE SECOND FRONT. SNOW LEVELS SHOULD FALL TO 5KFT ACROSS NW CAL
SAT NIGHT BEHIND THE COLD FRONT. THE GFS BASED SNOW LEVELS HAS IT
LOWER...DOWN TO 4.5KFT EARLY SUNDAY MORNING...HOWEVER THERE DOES
NOT APPEAR TO BE MUCH IF ANY PRECIP IN NE TRINITY FOR SUBSTANTIAL
SNOW AMOUNTS DURING THIS TIME FRAME. THE MODELS HAVE BEEN SHOWING
THIS TIME PERIOD TO BE THE DRIEST WITH PERHAPS ONLY ISOLATED OR
SCATTERED SHOWERS LATE SAT NIGHT INTO SUNDAY MORNING. WARM AIR
ADVECTION AND SOUTHERLY FLOW WILL DEVELOP DURING THE DAY ON SUNDAY
AND DRIVE SNOW LEVELS BACK UP TO 6KFT OR MORE.

THE 12Z ECMWF AND 12Z GFS WERE IN SLIGHTLY BETTER AGREEMENT SHOWING
PRECIP RAMPING UP AGAIN ON SUNDAY AS SHORT-WAVE EMANATING FROM A
LOW PRESSURE SYSTEM OVER THE CENTRAL PACIFIC APPROACHES THE
NORCAL COAST. THE NAM12 HAS PRECIP SPREADING NORTHWARD INTO MENDO
COUNTY BY MIDDAY SUNDAY AS WELL. THE PRECIP LOOKS TERRAIN DRIVEN
AND MOSTLY ON THE LIGHT SIDE...WITH THE BEST UPWARD MOTION FOR
MODERATE RAIN OFFSHORE OR NEAR THE COAST ALONG THE WARM FRONT.
THE MODELS CONTINUE TO SHOW SOUTHERLY UPSLOPE FLOW AND WEAK WARM
AIR ADVECTION CONTINUING SUN NIGHT INTO MONDAY...SO MAINTAINED
EQUAL CHANCES OF RAIN OR NO RAIN FOR THIS TIME FRAME.

THE 12Z MODELS WERE IN SLIGHTLY BETTER AGREEMENT TUE INTO WED
NEXT WEEK...HOWEVER THERE WERE STILL SIGNIFICANT TIMING
DIFFERENCES. ALL THE MODELS SHOW AN UPPER TROUGH DEVELOPING JUST
WEST OF 130W BY 12Z MONDAY. ALL DEVELOP A CLOSED LOW IN THE
SOUTHERN BRANCH OF THE SPLIT. ALL MODEL MOVE THIS TROUGH AND
CLOSED LOW TOWARD THE COAST TUE AND WED NEXT WEEK BUT VARY ON HOW
FAST. THE GFS HAS CONSISTENTLY BEEN THE FASTEST AND WETTEST. THE
ECMWF HAS BEEN SLOWER AND LESS BOLD WITH THE RAIN. THE NEW 12Z
ECMWF WAS SLIGHTLY FASTER NOW...BUT STILL SLOWER. IT DOES LOOK
LIKE WET AND UNSETTLED WEATHER CONDITIONS WILL CONTINUE INTO MID
NEXT WEEK. THE TIMING AND DURATION OF RAIN IS STILL VERY
QUESTIONABLE. BOOSTED PRECIP CHANCES UP SOME TO INDICATE MORE
CONFIDENCE THROUGH ABOUT WED...HOWEVER MAINTAINED A RATHER VAGUE
AND BROAD BRUSH FORECAST WITH NEARLY EQUAL CHANCES OF RAIN OR NO
RAIN AFTER THAT DUE TO LARGE MODEL DIFFERENCES. //END

&&

.AVIATION...ALL NW CAL REGIONAL AIRPORTS WILL CONTINUE TO BOUNCE
BETWEEN VFR AND IFR OVER THE COMING 24 HOURS DUE TO INCLEMENT
WEATHER CROSSING THE REGION. IFR DUE TO LOWER CIGS AND VSBY IS
EXPECTED DURING HEAVY SHOWERS WHILE CIGS AND VSBY ARE EXPECTED TO
LIFT BETWEEN SHOWERS OR IN PERIODS OF LIGHT RAIN. DEEP INTERIOR
VALLEYS WILL BE THE EXCEPTION WHERE LOW CIGS AND VSBY WILL BE THE
NORM. UKI BEING IN A BROAD VALLEY SHOULD BOUNCE WITH THE REST. THE
TAFS ATTEMPT TO REFLECT THE OVERALL PATTERN, BUT NOT SHOW FINE
TEMPORAL RESOLUTION AS SHOWERS CAN BE VERY TOUGH TO TIME. BFG

&&

.MARINE...A SERIES OF DISTURBANCES WILL CROSS THE COASTAL WATERS
THROUGH THE MIDDLE OF NEXT WEEK AS A VERY ACTIVE PATTERN REMAINS IN
PLACE. A COLD FRONT WILL DROP ACROSS THE REGION TONIGHT, PRECEDED BY
SOUTHWESTERLY WINDS. WINDS MAY BECOME GUSTY JUST AHEAD OF FRONTAL
PASSAGE. BEHIND THE FRONT ON SATURDAY MORNING, WINDS WILL SHIFT TO
THE NORTH AND INCREASE TO 15 TO 20 KT FOR A SHORT TIME WHICH WILL
ALSO CAUSE BUILDING STEEP NORTHERLY WAVES. OPTED NOT TO EXTEND THE
SMALL CRAFT BEYOND THIS EVENING AS THERE LOOKS TO BE A DECENT WINDOW
WHERE WINDS WILL DROP BELOW ADVISORY LEVEL BETWEEN THIS MORNINGS
FRONT AND TONIGHTS FRONT. THIS WILL BE A SHORT WIND NORTH OF CAPE
MENDOCINO FROM ABOUT 9 PM TO AROUND 3 AM, WHILE THE WINDOW SOUTH OF
THE CAPE WILL LAST LONGER. POTENTIALLY FROM 9 PM THROUGH LATE
SATURDAY MORNING. DURING THE TIME THE STEEP WIND DRIVEN WAVES WILL
SUBSIDE WHILE THE WESTERLY SWELL SLOWLY SUBSIDES INTO SATURDAY. UPON
EXPIRATION OF THE SMALL CRAFT ADVISORY THIS EVENING ANOTHER ONE WILL
LIKELY BE NEEDED FOR THE BACKSIDE OF THE WINDOW. AGAIN, WINDS WILL
POP UP BEHIND THE FRONT EARLY SAT MORNING TO LOW END SMALL CRAFT AND
LIKELY REMAIN THERE THROUGH MUCH OF THE DAY. THE COLD FRONT IS
FORECAST TO SINK INTO THE BAY AREA, STALL, THEN LIFT NORTH AS A WARM
FRONT ON SUNDAY. THIS WARM FRONT WILL BRING INCREASING EAST TO
SOUTHEAST WINDS AS IT LIFTS THROUGH SUNDAY INTO MONDAY. IF THESE
OFFSHORE WINDS PAN OUT, THERE WILL BE VERY LIMITED FETCH RIGHT UP
AGAINST THE COAST WHICH WILL SIGNIFICANTLY LIMIT THE DEVELOPMENT OF
STEEP WAVES IN THE WATERS DIRECTLY ADJACENT TO THE SHORE. FARTHER
OFFSHORE WILL ALLOW FOR MORE FETCH AND RAPIDLY BUILDING STEEP WAVES.
TRIED TO REFLECT THIS IN THE GRIDDED FORECAST AS MUCH AS POSSIBLE,
WHICH SHOWS SEAS OF 3 TO 6 FT ALONG THE HUMBOLDT AND DEL NORTE COAST
ON MONDAY. THE MENDOCINO COAST IS A BIT MORE EXPOSED TO THE SE
WINDS, SO SEAS ARE EXPECTED TO BE MORE IN THE 4 TO 7 FT RANGE.
AGAIN, THIS IS WITHIN A COUPLE MILES OF THE SHORE, NOT FARTHER OUT.
DURING THIS TIME OF STRONG SE FLOW, THERE IS AN OUTSIDE SHOT THAT A
HAZARDOUS SEAS WARNING MAY BE NEED FOR THE WATERS BEYOND 10 NM.
WE`LL SEE HOW MODELS HANDLE THIS PATTERN OVER THE NEXT COUPLE OF
DAYS. TUESDAY AND WEDNESDAY HAVE KEPT SOUTH TO SOUTHEAST FLOW IN THE
FORECAST SINCE MODELS ARE HAVING A TOUGH TIME RESOLVING THE
SPECIFICS OF THE PATTERN. SE WINDS ARE A COMPROMISE OF THE MODELS
WHICH FOLLOWS THE THINKING OF LOW PRESSURE MOVING TOWARD THE BAY
AREA. THIS WILL OBVIOUSLY BE REFINED OVER THE COMING DAYS. BFG

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PZZ450-455.

     SMALL CRAFT ADVISORY UNTIL 9 PM PST THIS EVENING FOR PZZ470-475.

&&

$$

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