Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 041149
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
449 AM PDT TUE AUG 4 2015

.SYNOPSIS...A WEAK UPPER LEVEL SYSTEM WILL BRING ISOLATED
AFTERNOON AND EVENING INLAND THUNDERSTORMS TODAY. WEAK RIDGING
WILL BRING DRY CONDITIONS WEDNESDAY AND THURSDAY WITH ANOTHER
SYSTEM FRIDAY INTO THE WEEKEND BRINGING ADDITIONAL SHOWERS AND
THUNDERSTORMS.

&&

.DISCUSSION...WATER VAPOR SHOWS A SHORTWAVE APPROACHING THE AREA
THIS MORNING FROM THE SOUTHWEST. THIS WILL BRING A SLIGHT CHANCE
FOR THUNDERSTORMS TO THE AREA THIS AFTERNOON AND EVENING. THE
LAPSE RATES AND CAPE LOOK THE BEST IN NORTHERN TRINITY COUNTY. THE
BEST INSTABILITY IS A BIT CLOSER TO THE COAST SO HAVE EXPANDED
THE SLIGHT CHANCE OF THUNDERSTORMS TO THE WEST. FARTHER SOUTH IN
MENDOCINO COUNTY HAVE ADDED A FEW SHOWERS TO THE FORECAST. THE
SHORTWAVE APPROACHING THE AREA IS FAIRLY STRONG...BUT
THERMODYNAMIC PROFILES ARE QUITE STABLE. ALSO THE BEST UPPER
LEVEL JET DYNAMICS ARE TO THE SOUTH OF THE AREA. SO LIGHT SHOWERS
LOOK TO BE THE MOST LIKELY. AS THIS WAVE APPROACHES THE COAST IT
WILL NEED TO BE WATCHED FOR CONVECTION. CURRENTLY IT DOES NOT LOOK
VERY CONVECTIVE. ALONG THE COAST THE DEEP MARINE LAYER IS EXPECTED
TO PERSIST THROUGH MUCH OF THE DAY WITH LITTLE CLEARING AT THE
IMMEDIATE COAST. TEMPERATURES WILL BE SIMILAR TO YESTERDAY OR
SLIGHTLY COOLER.

TONIGHT THE SHORTWAVE MOVES OFF TO THE EAST AND ANY SHOWERS THAT
FORM IN THE EVENING SHOULD END BY LATE EVENING. HIGH PRESSURE
STARTS TO BUILD IN BRIEFLY ON WEDNESDAY. THIS WILL START A WARMING
TREND ONCE AGAIN. DRY CONDITIONS ARE EXPECTED ACROSS THE AREA ON
WEDNESDAY. WEDNESDAY NIGHT INTO THURSDAY OFFSHORE FLOW STARTS TO
SET UP. THIS WILL CONTINUE THE DRYING AND WARMING TREND FOR
THURSDAY. THERE LOOKS TO BE A BETTER CHANCE FOR SKIES CLEARING AT
THE COAST WELL.

THURSDAY AFTERNOON AND EVENING AN UPPER LEVEL LOW APPROACHES THE
AREA. THE BEST CHANCE FOR THE THUNDERSTORMS LOOKS TO BE LATE IN
THE EVENING IN MENDOCINO COUNTY SO HAVE ADDED A SLIGHT CHANCE TO
THE FORECAST. THIS PATTERN ALSO BRINGS DRYING OFFSHORE
FLOW...ESPECIALLY TO AREAS NORTH OF CAPE MENDOCINO. THUNDERSTORMS
MAY SPREAD NORTH OVERNIGHT AND EXPAND ON FRIDAY AS THE UPPER LEVEL
LOW MOVES OVERHEAD. THESE STORMS LOOK TO BE FAIRLY DRY. THIS
PATTERN WILL NEED TO CONTINUE TO BE MONITORED.

FOR THE WEEKEND THE UPPER LEVEL LOW CONTINUES TO MOVE OFF TO THE
EAST AND AN UPPER LEVEL TROUGH STARTS TO SETTLE OVER THE AREA.
FLOW WILL MORE WEST TO NORTHWEST. THERE MAY BE A FEW LINGERING
THUNDERSTORMS OVER TRINITY COUNTY ON SATURDAY...BUT ON SUNDAY
EXPECTED THE THREAT WILL BE MORE LIMITED. THERE MAY BE A FEW RAIN
SHOWERS OVER TRINITY COUNTY ON SUNDAY.

EARLY NEXT WEEK MODELS ARE SHOWING ANOTHER UPPER LEVEL LOW
APPROACHING THE AREA FROM THE NORTHWEST. 00Z MODEL RUNS SHOWED
THIS LOW MOVING SOUTH AND REMAINING WELL OFFSHORE. HOWEVER THE 06Z
GFS RUN SHOWED IT SLOWLY MOVING ONSHORE IN THE PACIFIC NORTHWEST.
SO FOR NOW AM GOING WITH THE CONSENSUS AND SHOWING A WARMING AND
DRYING TREND EARLY NEXT...BUT CONFIDENCE IS LOWER NOW THAT I HAVE
SEEN THE 06Z GFS. MKK

&&

.AVIATION...A MODERATELY DEEP MARINE HAS ONCE AGAIN RESULTED IN
LOW CLOUDS PUSHING WELL INTO THE COASTAL RIVER VALLEYS THIS
MORNING. CEILINGS AT THE COAST HAVE BEEN MOSTLY AT OR ABOVE 1000
FEET. CEILINGS MAY BRIEFLY FALL BELOW 1000 FT AT KACV AND KCEC BY
DAYBREAK...BUT SHOULD SPRING BACK UP AND STAY MOSTLY IN THE MVFR
CATEGORY THROUGH THE DAY. LOW CLOUDS HAVE BEEN SLOWLY PRESSING
TOWARD UKIAH MUNI THIS MORNING FROM THE WEST. WITH AN UPPER TROUGH
APPROACHING THIS MORNING EXPECT MVFR CLOUD LAYERS TO SPILL OVER
THE COASTAL RANGE INTO UKIAH MUNI BY DAYBREAK. A DISTURBANCE
EMBEDDED WITHIN THIS TROUGH WILL MOVE ACROSS THE UKIAH AREA THIS
AFTERNOON. A FEW SHOWERS MAY DEVELOP IN THE VICINITY OF UKIAH OR
OVER THE MOUNTAINS TO THE EAST WITH DAYTIME HEATING. WEAK RIDGING
AND WARMING ALOFT ON WED MAY RESULT IN A SLIGHTLY SHALLOWER MARINE
LAYER AND PERHAPS BETTER CHANCES OF CLOUDS SCATTERING OUT AT THE
COAST AS NORTHERLY WINDS INCREASE OFFSHORE.

&&

.MARINE...SURFACE HIGH PRESSURE OVER THE NE PACIFIC WILL CONTINUE
TO BUILD TOWARD THE PACIFIC NW COAST TODAY THROUGH TONIGHT. BROAD
LOW PRESSURE THAT HAS BEEN OVER THE AREA FOR THE LAST SEVERAL DAYS
WILL SHIFT INTO THE INTERIOR THIS AFTERNOON AND EVENING. PRESSURE
GRADIENTS WILL TIGHTEN UP PRIMARILY OVER THE NORTHERN OUTER WATERS
TODAY AND THEN OVER THE SOUTHERN OUTER WATERS TONIGHT. THE
NORTHERLY WINDS STILL DO NOT LOOK EXCEPTIONALLY STRONG TODAY AND
TONIGHT BUT SEAS WILL START TO BUILD TO 6-8 FT WITH PERIODS AROUND
7 TO 8 SECONDS. THUS WILL MAINTAIN THE ADVISORY FOR PZZ470 AND
EXPAND IT TO THE SOUTHERN OUTER WATERS TONIGHT. THE GFS, ECMWF,
NAM12 AND SREF WERE IN FAIRLY GOOD AGREEMENT WITH NORTHERLY WINDS
REACHING 20-25 KT IN OUTER WATER ON WED. WINDS MAY INCREASE
FARTHER ON THU AS A THERMAL TROUGH INTENSIFIES ACROSS THE
INTERIOR. A GALE WATCH WILL NEED TO BE CONSIDERED IF THE MODELS
CONTINUE TO TREND IN THAT DIRECTION.

SEAS HAVE BEEN RUNNING AROUND 3 TO 4 FT AT 8 SECONDS THIS
MORNING. LONGER PERIOD SOUTHERLY WAVES AROUND 1-2 FT WERE ALSO IN
THE MIX. SHORT PERIOD NW SEAS WILL TREND UPWARD TODAY AND TONIGHT.
PER THE LATEST NWPS AND ENP...WAVE STEEPNESS WILL BE BELOW OUR
CRITERIA FOR HAZARDOUS SEAS INSIDE 10NM TONIGHT AND WED. IN THE
OUTER WATERS, BOTH MODELS INDICATE WIND DRIVEN SEAS INCREASING TO
6 TO 8 FT AT 8 SECONDS BY TONIGHT. SEAS WILL CONTINUE TO RAMP UP
ON WED AND THU. BASED ON OUR CRITERIA...A WARNING FOR HAZARDOUS
SEAS MAY BE NECESSARY IN THE OUTER WATERS IF SEAS REACH 10 FT OR
MORE WITH PERIODS OF 8 SECONDS OR LESS. WE HAVE BEEN FOLLOWING THE
NWPS GUIDANCE WHICH HAS WAVES REACHING 11 TO 13 FT AT 9 SECONDS ON
THU AND FRI IN PZZ470 AND PZZ475. THE ENP WAS A COUPLE OF FEET
LESS...BUT STILL NEAR CRITERIA FOR A WARNING. ONCE AGAIN IT IS
JUST OUTSIDE OUR WINDOW FOR ISSUING A HAZARDOUS SEAS WATCH.

CONDITIONS SHOULD EASE UP OVER THE WEEKEND NORTH OF THE CAPE.
SOUTH OF THE CAPE CONDITIONS APPEAR TO REMAIN MARGINAL FOR AN
ADVISORY. BOTH THE GFS AND ECMWF WERE IN DECENT AGREEMENT SHOWING
AN UPPER TROUGH BUSTING DOWN THE OFFSHORE RIDGE WITH GRADIENTS
LOOSENING UP CONSIDERABLY ACROSS NW CALIFORNIA WATERS THIS
WEEKEND.

&&

.FIRE WEATHER...THERE IS THE POTENTIAL FOR THUNDERSTORMS AGAIN
TODAY AS A SHORTWAVE MOVES THROUGH THE AREA. THE BEST CHANCE LOOKS
TO BE IN TRINITY COUNTY. THERE IS THE POTENTIAL FOR A FEW IN
MENDOCINO COUNTY AS WELL. THE DEEP MARINE LAYER IS EXPECTED TO
PERSIST TONIGHT.

WEDNESDAY THROUGH THURSDAY HIGH PRESSURE BRIEFLY BUILDS INTO THE
AREA BRIEFLY. THIS WILL WARM TEMPERATURES AND LOWER RH EACH DAY.
THIS WILL ALSO COMPRESS THE MARINE LAYER AND CONFINE IT TO THE
COAST A BIT MORE THAN ON PREVIOUS DAYS. WEDNESDAY NIGHT INTO
THURSDAY WINDS LOOK TO BECOME MORE EASTERLY AS THE UPPER LEVEL LOW
APPROACHES THE AREA. THIS WILL CAUSE RH RECOVERIES TO BE POOR
ESPECIALLY OVER THE HIGHER ELEVATIONS.

THURSDAY NIGHT AND FRIDAY THERE IS THE POTENTIAL FOR THUNDERSTORMS
ONCE AGAIN. THERE ARE STILL QUESTIONS ON LOCATION AND
COVERAGE...BUT CONFIDENCE IS GROWING. A RFW MAY NEEDED...BUT THIS
WILL NEED TO BE MONITORED AS IT GETS CLOSER. AN UPPER LEVEL TROUGH
IS EXPECTED TO BRING COOLER AND MORE DAMP WEATHER FOR THE WEEKEND.
MKK

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY FROM 8 AM THIS MORNING TO 11 PM PDT FRIDAY
     FOR PZZ470.

     SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 PM PDT FRIDAY
     FOR PZZ475.

&&

$$

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