Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 160222
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
722 PM PDT MON SEP 15 2014

.SYNOPSIS...A WEAKENING LOW PRESSURE SYSTEM OVER THE EASTERN
PACIFIC WILL BRING A CHANCE OF SHOWERS WED THROUGH THU. DRY
AND WARMER WEATHER WILL LIKELY RETURN ON FRIDAY AND SATURDAY.

&&

.UPDATE...QUICK UPDATE TO THE FORECAST TO PULL BACK CLOUD COVER
FOR THE EVENING AND LOWER INLAND TEMPS BY A FEW DEGREE FOR
TONIGHT. THE UPPER LOW MOVING TO THE NORTH IS PULLING CLOUDS ALONG
WITH IT...LEAVING THE NW CAL COAST WITH CLEAR SKIES THIS EVENING.
WEAK SURFACE RIDGING SHOULD ALLOW LOW CLOUDS AND FOG TO DEVELOP
ALONG THE IMMEDIATE COAST AGAIN IN THE VERY EARLY TUE MORNING
HOURS...SO HAVE LEFT THAT IN THE FORECAST. WINDS WILL EASE
OVERNIGHT AND SHOULD ALLOW FOR EFFECTIVE SURFACE COOLING ACROSS
INTERIOR VALLEYS. SO DIPPED THE LOW TEMPS DOWN A DEGREE OR TWO FOR
THE LOWS. DID NOT TOUCH THE ONGOING FORECAST BEYOND TONIGHT. BFG

&&

.PREV DISCUSSION......ISSUED AT 357 PM PDT...

SYNOPSIS...A WEAKENING LOW PRESSURE SYSTEM OVER THE EASTERN
PACIFIC WILL BRING A CHANCE OF SHOWERS WED THROUGH THU. DRY
AND WARMER WEATHER WILL LIKELY RETURN ON FRIDAY AND SATURDAY.

DISCUSSION...A VIGOROUS VORT MAX TRACKING NORTHWARD ALONG THE
SOUTHERN OREGON COAST THIS AFTERNOON KICKED UP THE SOUTHERLY
WINDS ACROSS THE INTERIOR ZONES TODAY. SOME OF THE VALLEYS NORTH
OF CAPE MENDO SAW GUSTS AROUND 35-38 MPH...WITH FAIRLY LOW RH`S IN
THE TEENS. MANY SITES WERE RUNNING SEVERAL DEGREES COOLER
TODAY...UP TO 15-20F COOLER AT A FEW RAWS THANKS TO THE DEEP
MIXING. THE VORT WILL CONTINUE TO TRACK NORTHWARD THIS EVENING
WITH THE GUSTY WINDS TAPERING OFF BY EARLY TO MID EVENING. THE
SOUTHERLY SURGE AHEAD OF THE FRONT ALSO HELP TO SCOUR OUT THE
STRATUS SOUTH OF THE CAPE AND AROUND EKA. A DEEP MARINE LAYER AND
HIGHER BOUNDARY LAYER RH`S WILL LIKELY LEAD TO MORE CLOUD
DEVELOPMENT AS WINDS DECOUPLE. THE CLOUDS SHOULD ALSO FORM AND
PUSH A LITTLE FARTHER INLAND TONIGHT. MIXING ON TUESDAY WILL BE
FAIRLY GOOD AGAIN WITH MOST OF THE CLOUDS DISSIPATING BY NOON. THE
MODELS CONTINUE WITH PREVIOUS TRENDS OF DIGGING AN UPPER TROUGH
WEST OF 130W AND SOUTH OF 40N ON TUE. THIS WILL PUT THE AREA IN
ROBUST SW FLOW ALOFT WHICH SHOULD PROMOTE MORE MARINE AIR COOLING.
850MB TEMPERATURES FROM THE GFS AND NAM12 REMAIN AROUND 20C ON
TUE AND A FEW LOWER TO MID 90S ARE STILL POSSIBLE IN ZONES 277 AND
283. EVEN THE DAYTIME RH`S DO NOT LOOK TO CHANGE A WHOLE LOT
EITHER WITH MIN RH`S LIKELY IN THE TEENS WHERE MARINE AIR HAS NO
IMPACT.

THE MODELS CONTINUE TO SHOW A WEAK WAVE IN THE SW FLOW CLIPPING
THE NW CORNER OF THE AREA TUE AFTERNOON AND EVENING. IT IS LOOKS
TOO DRY FOR ANY PRECIP WITH THIS WAVE. HOWEVER I DID KEEP MOSTLY
5-10% FOR THE POSSIBILITY OF A FEW SPRINKLES. THE MAIN STORY
WILL BE THE CHANCE OF RAIN AROUND MID WEEK. THE MODELS CONTINUE TO
TREND WETTER FOR WED AFTERNOON AS THE LOW ALOFT APPROACHES CAPE
MENDO. THE GFS AND ECMWF WERE IN BETTER AGREEMENT...HOWEVER THE
NAM12 WAS AN OUTLIER. CONFIDENCE IS NOT HIGH THIS LOW WILL BRING A
LOT OF RAIN OR THAT IT WILL BE A LONG LASTING. THE FIRST BAND OF
PRECIP LOOKS TO COME IN AROUND CAPE MENDO WED AFTERNOON AND
EVENING. THIS FEATURE COULD PRODUCE A FEW HUNDREDTHS TO TENTH OF
AN INCH. ANOTHER SHOT OF PRECIP WILL COME IN WITH THE MID LEVEL
TROUGH ON WED NIGHT OR THU MORNING AS TEMPERATURES ALOFT COOL AND
INSTABILITY INCREASES. WE COULD SEE ANOTHER TENTH OR SO NORTH OF
THE CAPE. CONDITIONS SHOULD BEGIN TO DRY OUT AND STABILIZE QUICKLY
THU NIGHT AS HIGH PRESSURE BUILDS IN RAPIDLY BEHIND THE LOW.

LONG TERM (FRI THRU MON)...HIGH PRESSURE WILL BEGIN TO BUILD OVER
NORTHWEST CALIFORNIA ON FRIDAY AS THE UPPER TROUGH SLIDES OFF TO THE
SOUTH AND EAST...EVENTUALLY DEVELOPING INTO A CUT OFF LOW OVER
SOUTHERN CALIFORNIA FOR THE WEEKEND. MODELS BEGIN TO DIVERGE LATER
ON SATURDAY WITH THE GFS TAKING THE LOW OFF TO THE EAST...WHILE THE
ECMWF RETROGRADES THE LOW BACK TO THE WEST AND EVENTUALLY OFFSHORE.
REGARDLESS...BOTH SOLUTIONS NOW KEEP THE AREA DRY INTO EARLY NEXT
WEEK WITH BUILDING HEIGHTS AND ABOVE NORMAL HIGH TEMPERATURES
RETURNING FOR INTERIOR LOCATIONS. STP

AVIATION...AN UPPER LEVEL SYSTEM HAS MIXED OUT SOME OF THE
COASTAL STRATUS RESULTING IN PARTIAL CLEARING...PARTICULARLY FROM
HUMBOLDT BAY SOUTH. THE COASTAL CLOUDS WILL LIKELY REDEVELOP
OVERNIGHT...BUT WITH ENHANCED MIXING WITH THE UPPER LEVEL SYSTEM
NEARBY...THE CEILINGS LIKELY WILL NOT FALL AS LOW AS PREVIOUS
DAYS. MOST AREAS IN THE INTERIOR WILL REMAIN VFR THOUGH SOME
STRATUS WILL LIKELY CREEP UP COASTAL VALLEYS AND POSSIBLY FROM THE
SOUTH INTO INTERIOR MENDOCINO COUNTY TO NEAR UKIAH. BETTER MIXING
ON TUESDAY WILL LIKELY RESULT IN AT LEAST PARTIAL CLEARING OVER
THE ENTIRE AREA BY AFTERNOON. RPA

MARINE...AN UPPER LEVEL SYSTEM AND SURFACE LOW WILL APPROACH THE
AREA TUESDAY INTO WEDNESDAY ALLOWING LIGHT TO MODERATE SOUTHERLY
WINDS TO PERSIST OVER THE WATERS. SHORT PERIOD SEAS WILL BUILD IN
RESPONSE...BUT AT THIS TIME SEAS AND WINDS ARE ANTICIPATED TO REMAIN
JUST BELOW SMALL CRAFT CRITERIA. HOWEVER...A SLIGHT CHANGE IN THE
STRENGTH OF THE SURFACE LOW COULD RESULT IN SMALL CRAFT WINDS IN THE
OUTER WATERS FOR A FEW HOURS ON WEDNESDAY. THE LOW WILL WEAKEN ON
THURSDAY AND MOVE INLAND ALLOWING WINDS TO TURN BACK OUT OF THE
NORTH AND INCREASE. SMALL CRAFT WINDS AND SEAS ARE LIKELY IN THE
OUTER WATERS FOR AT LEAST A SHORT PERIOD FRIDAY INTO SATURDAY.

A SOUTHWESTERLY LONG PERIOD WAVE SYSTEM HAS BEGUN TO MOVE THROUGH
THE WATERS AROUND 2-3 FT AT 20-22 SECONDS. THE SNEAKER WAVE THREAT
APPEARS SMALL WITH THIS WAVE SYSTEM...THOUGH INCREASED CURRENTS WILL
BE A HIGH HAZARD FOR THOSE VENTURING INTO THE SURF ZONE...SUCH AS
ABALONE DIVERS. THE WAVE SYSTEM WILL SLOWLY DECAY IN PERIOD AND
MAGNITUDE THROUGH THE END OF THE WEEK. RPA

&&

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

$$

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