Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 232230
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
330 PM PDT TUE SEP 23 2014

.SYNOPSIS...A LOW PRESSURE TROUGH AND FRONTAL BOUNDARY WILL MOVE
OVER THE NORTHWEST CALIFORNIA COAST TONIGHT AND WEDNESDAY. THE
FRONTAL BOUNDARY WILL PRODUCE COOLER TEMPERATURES AND RAIN TO
NORTHWEST CALIFORNIA TONIGHT AND WEDNESDAY. WIDESPREAD RAIN WILL
OCCUR OVERNIGHT THROUGH THURSDAY MORNING FOLLOWED BY THE THREAT OF
SHOWERS CONTINUING INTO THE WEEKEND.


&&

.SHORT TERM...A DEEP MOISTURE LAYER ASSOCIATED WITH A LOW
PRESSURE TROUGH AND FRONTAL BOUNDARY IS APPROACHING NORTHWEST
CALIFORNIA THIS AFTERNOON. THESE SYSTEMS WILL PRODUCE SHOWERS
THIS EVENING AND WIDESPREAD RAIN ACROSS THE REGION TONIGHT
THROUGH WEDNESDAY NIGHT. RAINFALL AMOUNTS UP TO 1 TO 2 INCHES MAY
OCCUR ACROSS SOME AREAS THE NEXT FEW DAYS WITH UP TO 3 INCHES
ACROSS SOME ELEVATED AREAS ACROSS DEL NORTE COUNTY. THE LOW
PRESSURE TROUGH IS FORECAST TO REMAIN HIGHLY AMPLIFIED. THE MOST
PERSISTENT AND HEAVIEST PRECIPITATION WILL OCCUR OVER THE TERRAIN
OF DEL NORTE COUNTY WHERE STORM TOTALS IN EXCESS OF 3 INCHES ARE
POSSIBLE.

PRECIPITATION WILL TRANSITION FROM STRATIFORM TO SHOWERS BY
THURSDAY. MINIMAL MUCAPE VALUES ARE ANTICIPATED THRU THE
PERIOD...SO HAVE CONTINUED TO KEEP THUNDER OUT OF THE FORECAST.
HAVE MADE MINOR ADJUSTMENTS TO TEMPERATURES AND POPS INTO THE
EXTENDED FORECAST PERIOD.


.LONG TERM (FRI THRU MON)...MODEL GUIDANCE IS IN FAIRLY GOOD
AGREEMENT ON FRIDAY WITH A POST FRONTAL TROUGH OVER THE REGION
CONTINUING THE CHANCES FOR RAIN SHOWERS. BY SATURDAY UNCERTAINTY
IN THE FORECAST INCREASES AS MODELS BEGIN TO DIVERGE. THE GFS IS
MUCH MORE PROGRESSIVE AND CUTS THE TROUGH INTO AN UPPER LOW OVER
THE INTERMOUNTAIN WEST WHILE THE ECMWF SLIDES THE TROUGH
EASTWARD...BUT KEEPS CALIFORNIA UNDER A NORTHWEST FLOW PATTERN.
THE DIFFERENCES BETWEEN THE TWO SOLUTIONS COULD GIVE NORTHWEST
CALIFORNIA VERY DIFFERENT WEATHER FOR THE WEEKEND. IF THE GFS IS
CORRECT...RIDGING WILL BUILD OVER THE WEST COAST WITH DRY WEATHER
AND WARMING TEMPERATURES. WITH THE ECMWF...COOLER TEMPERATURES AND
SOME PRECIP CHANCES CONTINUE. RMOP TOOL SHOWS HIGH PREDICTABILITY
IN LOWER HEIGHTS SHIFTING EAST FOR THIS TIME FRAME BUT LOW
PREDICTABILITY IN THE OVERALL PATTERN OVER THE WEST COAST. HAVE
COMPROMISED BETWEEN THE TWO KEEPING SLIGHT CHANCE/CHANCE POPS OVER
THE INTERIOR THROUGH THE WEEKEND. HAVE KEPT TEMPERATURES CLOSE TO
PREVIOUS FORECAST DUE TO THE UNCERTAINTY. STP


&&


.AVIATION...MVFR TO VFR CONDITIONS HAVE BEEN FOUND ACROSS THE AREA
TODAY WITH -SHRA AND VCSH THIS MORNING GIVING KCEC SOME MVFR CIGS.
21Z VISIBLE SATELLITE IMAGERY SHOWED A WELL-DEFINED UPPER LEVEL LOW
NEAR 140 W AND 45 N WITH ASSOCIATED MID TO HIGH CLOUDS STREAMING
OVER THE AREA. SOUTHERLY PRE-FRONTAL WINDS HAVE BEGUN INCREASING
THIS AFTERNOON AND WILL CONTINUE INTO THE OVERNIGHT...STRONGEST AT
KCEC WHERE GUSTS UP TO 30 KTS ARE POSSIBLE. CONDITIONS WILL
GRADUALLY DETERIORATE OVERNIGHT AS A COLD FRONT ASSOCIATED WITH THE
AFOREMENTIONED LOW APPROACHES NORTHWEST CALIFORNIA. MVFR TO IFR
CONDITIONS ARE POSSIBLE OVERNIGHT WITH STEADY RAIN BEGINNING TO
IMPACT KCEC AROUND 8 TO 10 Z AND SPREADING TO THE SOUTH AND EAST
OVERNIGHT. STP


&&

.MARINE...SEAS STILL LOW AT 4 TO 6 FEET WITH DOMINATE PERIOD NEAR 8
SECONDS. SHORT PERIOD SEAS ARE STARTING TO BE OBSERVED NEAR CAPE
MENDO AND NORTH TO BUOY 22 WHERE THE PERIOD IS AT 5-6 SECONDS. THIS
TREND WILL EXPAND TO ALL WATERS LATER THIS EVENING AS SOUTHERLY
WINDS INCREASE AHEAD OF AN APPROACHING FRONTAL SYSTEM. FRONT IS
EXPECTED TO PASS THROUGH THE WATERS BETWEEN ABOUT 10 PM AND SUNRISE.
WINDS AND SEAS CONTINUE TO LOOK STRONGEST NORTH OF CAPE MENDO AND IN
THE OUTER WATERS. WITH EARLIER INCREASE IN WINDS EXPANDED SMALL
CRAFT ADVISORY FOR WINDS TO ALL OUTER WATERS AND NORTHERN INNER
WATERS THIS AFTERNOON THROUGH ABOUT MIDNIGHT. THIS IS A LITTLE
FASTER THAN EARLIER FORECAST. SMALL CRAFT WILL EXTEND TO ALL WATERS
FOR HAZARDOUS SEAS WEDNESDAY AS WESTERLY SWELL FROM A VIGOROUS FALL
STORM ARRIVES. OPC ANALYZED SEAS TO HAVE MAXED OUT AT 39 FEET ABOUT
8AM THIS MORNING WHICH IS ABOUT 9 FEET HIGHER THAN MODELS WERE
FORECASTING. WILL INCREASE SWELL HEIGHTS ABOUT A FOOT TO 14-16 FEET
RANGE NEAR 15 SECONDS BUT WON`T HAVE A BETTER SENSE IF I NEED TO GO
HIGHER UNTIL SWELL PASSES BUOY 02 LATER THIS AFTERNOON. THE WAVE
MODEL GUIDANCE CONTINUES TO SHOW SEAS TRENDING DOWNWARD ON THU. SEE
NO REASON AT THIS POINT TO DEVIATE FROM THE GUIDANCE. IT WILL STILL
REMAIN ELEVATED AND STEEP.

THE MODELS CONTINUE TO INDICATE A COUPLE OF SURFACE TROUGHS CLIPPING
THE NORTHERN ZONES THU INTO FRI. DIRECT OUTPUT FROM THE MODELS HAS
WINDS MOSTLY AROUND 15 KT AND WENT WITH THESE LIGHTER WINDS. GFS
CONTINUES TO CONSISTENTLY TREND TOWARD INCREASING N-NWLY WINDS THIS
WEEKEND. THE ECMWF HAS BEEN WEAKER WITH THE N-NW WINDS...SO BLENDED
IN SOME OF THE LIGHTER ECMWF WINDS INTO THE FORECAST.

HAVE GONE AHEAD AND ISSUED A HIGH SURF ADVISORY FOR THE COAST
WEDNESDAY AS THESE HIGH SEAS WITH LONG PERIODS COME INTO THE COAST.
THE SURF WILL REACH 20 TO 22 FT AND WILL RUN UP HIGHER ON THE BEACH
THAN WOULD BE EXPECTED WITH CURRENT SUMMERTIME SHALLOWER BEACH
SLOPE. DEAN


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
     HIGH SURF ADVISORY FROM 8 AM TO 8 PM PDT WEDNESDAY FOR
     CAZ001-002.

NORTHWEST CALIFORNIA COASTAL WATERS...
     HIGH SURF ADVISORY FROM 8 AM TO 8 PM PDT WEDNESDAY FOR
     PZZ410-450-455.

     SMALL CRAFT ADVISORY FROM 5 AM WEDNESDAY TO 9 PM PDT THURSDAY
     FOR PZZ455.

     SMALL CRAFT ADVISORY UNTIL 9 PM PDT THURSDAY FOR PZZ450-470-475.

&&

$$

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