Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 051134
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
434 AM PDT WED AUG 5 2015

.SYNOPSIS...WEAK RIDGING WILL BRING DRY AND WARMING CONDITIONS
TODAY AND THURSDAY. ANOTHER SYSTEM WILL IMPACT NORTHERN
CALIFORNIA THURSDAY NIGHT AND FRIDAY BRINGING ADDITIONAL SHOWERS
AND POSSIBLE THUNDERSTORMS THROUGH THE WEEKEND.

&&

.DISCUSSION...WATER VAPOR SHOWED A FAIRLY VIGOROUS SHORTWAVE
MOVING THROUGH THE AREA EARLIER...BUT NOW IT HAS PASSED OFF TO THE
EAST. A SHORT PERIOD OF UPPER LEVEL RIDGING HAS STARTED TO BUILD
INTO THE AREA AHEAD OF THE NEXT UPPER LEVEL LOW THAT IS WELL OFF
THE COAST THIS MORNING. TEMPERATURES WILL WARM IN MENDOCINO COUNTY
OVER YESTERDAY WITH HIGHS AROUND 90 AND MUCH LOWER RH IN THE
AFTERNOON. THE SUBSIDENCE AND SLIGHTLY INCREASED NORTHERLY WINDS
AT THE COAST BEHIND THIS SYSTEM MAY BRING A FEW BREAKS IN THE
CLOUDS AT THE COAST...BUT THESE ARE EXPECTED TO BE LIMITED.

TONIGHT BETTER OFFSHORE FLOW IS EXPECTED...ESPECIALLY IN DEL NORTE
COUNTY. THIS WILL LIKELY LIMIT STRATUS ON THE DEL NORTE
COAST...ALTHOUGH SOME NEARSHORE SOUTHERLY WINDS MAY KEEP SOME
STRATUS AROUND. THURSDAY TEMPERATURES WILL CONTINUE TO RISE AS
THE RIDGE STRENGTHENS A BIT. THE COAST HAS A BETTER CHANCE OF
CLEARING THURSDAY AFTERNOON WITH THE WEAK OFFSHORE FLOW. THIS IS
EXPECTED TO BE THE WARMEST DAY OF THE WEEK IN THE INLAND AREAS.

THURSDAY NIGHT INTO FRIDAY THE NEXT UPPER LEVEL LOW STARTS TO
APPROACH THE AREA. THIS STILL LOOKS TO HAVE THE POTENTIAL TO BRING
A FEW NOCTURNAL THUNDERSTORMS TO THE AREA. MODELS HAVE TRENDED
SLIGHTLY SOUTH WITH THIS UPPER LEVEL LOW SO THE BEST CHANCES LOOK
TO BE SOUTH OF OUR AREA. TRIMMED POPS BACK A BIT IN TRINITY COUNTY
AND EXPANDED THEM A BIT IN MENDOCINO COUNTY LATE THURSDAY NIGHT
AND EARLY FRIDAY MORNING. CONFIDENCE REMAINS LOW DUE TO THE
CHALLENGES OF NOCTURNAL CONVECTION AND UNCERTAINTY IN THE TRACK OF
THE LOW. FRIDAY AFTERNOON MODELS ARE STILL INDICATING SOME MODEST
CONVECTION IN THE EASTERN AREAS...HOWEVER THE UPPER LEVEL HAS
MOVED TO THE EAST OF THE AREA AND FLOW IS OUT OF THE NORTHWEST.
THIS IS NOT A TYPICAL PATTERN FOR THUNDERSTORMS AND THERMODYNAMIC
PROFILES DO NOT LOOK PARTICULARLY FAVORABLE SO IF THIS TREND
CONTINUES POPS MAY NEED TO BE TRIMMED BACK.

SATURDAY THE FLOW BECOMES ZONAL AS THE LOW MOVES TO THE EAST OF
THE AREA. THIS LOOKS TO BE TOO DRY FOR THUNDERSTORMS SO HAVE
TRIMMED THEM BACK TO MAINLY JUST THE NORTHERN MOST PORTIONS OF
TRINITY COUNTY. SUNDAY AN UPPER LEVEL TROUGH STARTS TO DIG OFF THE
COAST KEEPING THE AREA IN A FAIRLY DRY AND STABLE FLOW. WITH THE
WEAK FLOW AND LOWERING HEIGHTS THE MARINE LAYER IS EXPECTED TO BE
FAIRLY DEEP WITH ONLY MINIMAL AFTERNOON CLEARING AT THE COAST.

EARLY NEXT WEEK MODELS SHOW ANOTHER UPPER LEVEL LOW
FORMING...HOWEVER THE TRACK OF THE LOW KEEPS CHANGING FROM RUN TO
RUN AND MODEL TO MODEL. THERE SEEMS TO BE TWO SCENARIOS THAT
MODELS KEEP FLIP FLOPPING BETWEEN. ONE...THE UPPER LEVEL LOW
APPROACHES THE AREA AND THEN RETROGRADES TO THE WEST. THIS BRINGS
US BACK TO WEAK RIDGING AND FAIRLY DRY OFFSHORE FLOW. THE OTHER
SOLUTION BRINGS THE LOW ONTO THE COAST AND MUCH COOLER
TEMPERATURES ALTHOUGH THERE STILL ISNT MUCH CONVECTION. GIVEN THE
RECENT PATTERNS OF UPPER LEVEL LOWS SITTING AND SPINNING OFF THE
COAST GENERALLY FAVOR THE FIRST SOLUTION. THE 00Z GFS SHOWED THIS
SOLUTION WHILE THE 00Z ECMWF WAS A COMPROMISE BETWEEN THE TWO
SCENARIOS. THE 06Z GFS WAS DRASTICALLY DIFFERENT BRINGING A VERY
DEEP LOW JUST OF THE PACIFIC NW WHICH LOOKS UNLIKELY. 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 NEAR 1000 FEET.
CEILINGS WILL FLUCTUATE AROUND BELOW 1000 FEET AT KACV AND KCEC
THIS MORNING...THEN SPRING BACK UP AND STAY MOSTLY IN THE MVFR
CATEGORY THROUGH THE DAY. INCREASING NORTHERLY WINDS OFFSHORE WILL
PROVIDE MORE MECHANICAL MIXING TODAY AND MAY RESULT IN SCATTERED
TO BROKEN SKY CONDITIONS THIS AFTERNOON. WITH THE HIGH RESOLUTION
MODELS SHOWING HIGH BOUNDARY LAYER HUMIDITIES PERSISTING THROUGH
THE DAY CONFIDENCE IS NOT HIGH IN COMPLETE CLEARING. KCEC DOES
STAND THE BEST CHANCE TO SCATTER OUT TODAY WHILE KACV...KEKA AND
THE MENDO COAST STAND THE LEAST CHANCE. ONCE AGAIN DUE TO THE HIGH
BOUNDARY LAYER HUMIDITIES EXPECT STRATUS TO REFORM AND GROW
TONIGHT ALONG THE COAST. OFFSHORE FLOW DEVELOPING TONIGHT AROUND
THE KCEC AREA MAY INHIBIT WIDESPREAD STRATUS DEVELOPMENT THERE.
HOWEVER SOUTHERLY FLOW WILL PROBABLY ADVECT STRATUS NORTHWARD INTO
THE KCEC AIRPORT. THU IS STILL LOOKING MUCH BETTER FOR CLEARING
THROUGH THE DAY AS A THERMAL TROUGH BUILDS OVER THE NORTH COAST
AND OFFSHORE FLOW STRENGTHENS.

LOW CLOUDS HAVE BEEN BANKED UP AGAINST THE COASTAL RANGE WEST OF
UKIAH THIS MORNING. CLOUDS WERE ALSO NORTH OF UKIAH IN THE WILLITS
AREA. WITH THE NORTH FLOW...SLIGHT WARMING ALOFT AND A LESS DEEP
MARINE LAYER...CONFIDENCE IS LOW THAT UKIAH MUNI WILL RECEIVE BROKEN
OR OVERCAST LOW CLOUDS THIS MORNING. THUS WILL TOSS IN SCATTER LOW
CLOUDS THROUGH 16Z AS A HEADS UP THAT LOW CEILINGS ARE IN THE
VICINITY...MAINLY NORTH IN WILLITS AREA. INCREASING NORTH FLOW
TONIGHT AND THU AS WELL AS A DIMINISHING MARINE LAYER DEPTH WILL
KEEP LOW CLOUDS OUT OF UKIAH.

&&

.MARINE...SURFACE HIGH PRESSURE OVER THE NE PACIFIC WILL CONTINUE
TO BUILD TOWARD THE COAST TODAY THROUGH THU AS THERMAL LOW
PRESSURE DEVELOPS ACROSS THE INTERIOR. PRESSURE GRADIENTS WILL
TIGHTEN UP PRIMARILY OVER THE OUTER WATERS TODAY AND TONIGHT. THE
NORTHERLY WINDS STILL DO NOT LOOK EXCEPTIONALLY STRONG IN THE
OUTER WATERS TODAY BUT SEAS WILL BUILD TO 7-8 FT WITH PERIODS
AROUND 7 TO 8 SECONDS. THUS WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR HAZARDOUS SEAS IN THE OUTER WATERS. SCATTEROMETER WIND PASS
FROM TUE EVENING INDICATED WINDS IN THE 15 TO 20 KT RANGE MOSTLY
NORTH OF CAPE MENDO. THIS WAS IN FAIRLY GOOD AGREEMENT WITH THE
GFS AND NAM12 SURFACE WINDS. ALL THE MODELS CONTINUE TO INDICATE
NORTHERLY WINDS APPROACHING LOW END GALE IN THE NORTHERN OUTER
WATERS THU AFTERNOON AND EVENING. WITH SEAS EXPECTED TO RAMP UP TO
11 FT AT 8 SECONDS DURING THE DAY IN PZZ470...STARTED THE GALE
WARNING THU MORNING TO ACCOUNT FOR THE LARGE STEEP SEAS. NWPS AND
HIGH RESOLUTION ENP CONTINUE TO INDICATE WIND-DRIVEN SEAS PEAKING
AROUND 10-13 FT THU NIGHT IN PZZ470. SEAS WILL ALSO BUILD TO 8-9
FT IN PZZ450...SO HOISTED AN ADVISORY FOR HAZARDOUS SEAS INSIDE
10NM NORTH OF CAPE MENDO. BASED ON OUR CRITERIA...A WARNING FOR
HAZARDOUS SEAS MAY BE NECESSARY FOR THE OUTER WATERS SOUTH OF THE
CAPE WHERE THE NWPS HAS SEAS PEAKING TO 10-12 AT 8-9 SECONDS THU
NIGHT. CONFIDENCE HERE IS NOT ALL THAT HIGH SO WILL HOLD OFF ON
THE WARNING. EVEN THOUGH NORTHERLY WINDS DIMINISH A TAD ON
FRI...SEAS WILL REMAIN ROUGH AND STEEP. CONDITIONS WILL EASE UP
SUBSTANTIALLY THIS WEEKEND NORTH OF THE CAPE...AND EVENTUALLY
SOUTH OF THE CAPE. NW WINDS AND SEAS WILL PROBABLY REMAIN NEAR
SMALL CRAFT ADVISORY CRITERIA ON SAT SOUTH OF CAPE MENDO. AN UPPER
TROUGH FROM THE GULF OF AK WILL SLOWLY DIG SOUTHWARD AND BUST DOWN
THE OFFSHORE RIDGE WITH GRADIENTS LOOSENING UP ESPECIALLY NORTH OF
THE CAPE THIS WEEKEND. EVEN THOUGH WINDS EASE UP OFFSHORE...THIS
SORT OF PATTERN TYPICALLY PRODUCES BRISK AFTERNOON SEA BREEZES AT
THE COAST OVER LAND AREAS.

&&

.FIRE WEATHER...WEAK HIGH PRESSURE IS BUILDING INTO THE AREA THIS
MORNING. THIS WILL BRING WARMING TEMPERATURES AND LOWER RHS.
TONIGHT OFFSHORE FLOW AND RISING HEIGHTS WILL COMPRESS THE MARINE
LAYER AND CONFINE IT MORE TO THE COAST. THIS WILL RESULT IN POOR
RH RECOVERIES AND SLIGHTLY INCREASED WINDS OVER THE HIGHER
ELEVATIONS NEAR THE COAST TONIGHT. THURSDAY NIGHT THROUGH FRIDAY
THERE IS THE CHANCE FOR THUNDERSTORMS AS THE NEXT UPPER LEVEL LOW
STARTS TO APPROACH THE AREA. RECENT MODEL RUNS HAVE TRENDED THIS
LOW FARTHER SOUTH REDUCING THE THREAT FOR CONVECTION. THIS WILL
NEED TO BE MONITORED AS IT GETS CLOSER. FOR NOW HAVE ONLY MADE
SLIGHT CHANGES TO FORECAST AND KEPT THE THUNDERSTORMS LIMITED TO
SLIGHT CHANCE. MKK

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY FROM 2 PM THURSDAY TO 9 PM PDT FRIDAY FOR
     PZZ450.

     SMALL CRAFT ADVISORY UNTIL 8 AM PDT THURSDAY FOR PZZ470.

     GALE WARNING FROM 8 AM THURSDAY TO 3 PM PDT FRIDAY FOR PZZ470.

     SMALL CRAFT ADVISORY UNTIL 11 AM PDT SATURDAY FOR PZZ475.

&&

$$

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