Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 032257
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
357 PM PDT MON AUG 3 2015

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


&&

.SHORT TERM...(THROUGH THURSDAY) THE FIRST IN A SERIES OF WEAK UPPER
LEVEL FEATURES HAS MOVED THROUGH THE REGION AND IS NOW TRIGGERING
STORMS IN SISKIYOU COUNTY AND SOUTHERN OREGON. BETTER MIXING BEHIND
THIS SYSTEM HAS RESULTED IN BETTER CLEARING OF THE SMOKE AND THUS
MORE INSTABILITY OVER THE HIGHER PEAKS. AN ISOLATED SHOWER OR
THUNDERSTORM WILL BE POSSIBLE THROUGH THE AFTERNOON AND EARLY
EVENING HOURS...BUT IN GENERAL DRY CONDITIONS ARE EXPECTED THROUGH
TUESDAY MORNING. ANOTHER SHORTWAVE TROUGH WILL MOVE OVERHEAD ON
TUESDAY LEADING TO ANOTHER SLIGHT CHANCE OF THUNDERSTORMS OVER THE
INTERIOR. MUCH LIKE TODAY THE TIMING OF THE SHORTWAVE PASSAGE WILL
HAVE A MAJOR INFLUENCE ON THE POTENTIAL FOR STORMS AND CURRENTLY THE
MODELS INDICATE THIS SHORTWAVE WILL MOVE THROUGH THE AREA IN THE MID
AFTERNOON HOURS...PROVIDING THE TRIGGER THAT COULD INITIATE STORMS
DURING PRIME HEATING. SO THUNDERSTORM CHANCES HAVE A BIT MORE AREAL
COVERAGE TOMORROW OVER THE INTERIOR BUT STILL ONLY ISOLATED STORMS
ARE ANTICIPATED.

THESE SHORTWAVE TROUGHS WILL ALSO KEEP THE MARINE LAYER DEEP ALONG
THE COAST...PUSHING STRATUS WELL INLAND TONIGHT AND TUESDAY NIGHT
ACROSS MENDOCINO AND INTERIOR SOUTHERN HUMBOLDT COUNTY.

A SHORTWAVE RIDGE WILL MOVE OVER NORTHWEST CALIFORNIA WEDNESDAY INTO
THURSDAY LIKELY LEADING TO A SLIGHT COMPACTION OF THE MARINE LAYER
AND SUBSIDENCE OVER THE INTERIOR RESTRICTING STORM FORMATION. THUS
THE FORECAST IS DRY FOR WEDNESDAY AND THURSDAY.

A MORE POTENT UPPER LEVEL LOW WILL APPROACH THE COAST THURSDAY
NIGHT. DIFFLUENT FLOW ON THE EAST SIDE OF THE UPPER LOW WILL MOVE
OVER THE CENTRAL CALIFORNIA COAST THURSDAY NIGHT...AND DEPENDING ON
THE MID LEVEL LAPSE RATES...MAY ALLOW NOCTURNAL CONVECTION TO FORM
OVER MENDOCINO COUNTY AND POSSIBLY SOUTHERN HUMBOLDT AND TRINITY
COUNTIES. THIS POTENTIAL WILL BE WATCHED CLOSELY OVER THE NEXT FEW
DAYS AND THUNDERSTORMS MAY NEED TO BE INTRODUCED TO THE
OFFICIAL FORECAST. RPA

.LONG TERM...(FRIDAY THROUGH MONDAY)...FRIDAY AN UPPER LEVEL LOW
JUST OFF OF THE CENTRAL CALIFORNIA COAST WILL MOVE INLAND, JUST TO
OUR SOUTH. THIS LOW WILL BRING INSTABILITY TO OUR AREA WHILE ALSO
TAPPING INTO SOME SUBTROPICAL MOISTURE. INCREASED THE AREAL COVERAGE
FOR THUNDERSTORMS ON FRIDAY TO ACCOUNT FOR THIS, BUT KEPT THE SLIGHT
CHANCE WORDING FOR NOW. AS THE LOW MOVES INLAND THE MODELS HINT AT
NOCTURNAL THUNDERSTORMS FRIDAY NIGHT, FOLLOWED BY ANOTHER ROUND OF
STORMS ON SATURDAY. BUT THIS LOOKS TO REMAIN MAINLY OVER EASTERN
TRINITY COUNTY FOR NOW. LATE SATURDAY INTO SUNDAY AN UPPER LEVEL
TROUGH STARTS TO SETTLE OVER THE PACIFIC NORTHWEST. THIS WILL LEAD
TO INTERIOR TEMPERATURES SLIGHTLY BELOW NORMAL. BUT IT WILL ALSO
CONTINUE THE SLIGHT CHANCE OF THUNDERSTORMS ACROSS MAINLY TRINITY
COUNTY EACH AFTERNOON AND EARLY EVENING. THE THING TO NOTE IS
NORTHWEST FLOW IS NOT A PARTICULARLY FAVORABLE PATTERN FOR
THUNDERSTORMS, SO THIS WILL NEED TO BE WATCHED.


&&

.AVIATION...AFTERNOON VISIBLE SATELLITE IMAGERY SHOWS STRATUS ALONG
PORTIONS OF THE COAST WHILE THE INTERIOR HAS A MIX OF MOSTLY CLEAR
SKIES, SOME CUMULUS CLOUDS, AND SMOKE/HAZE FROM MULTIPLE FIRES.
ALONG THE COAST...STRATUS WILL OVERSPREAD THE ENTIRE COAST WHILE
ALSO BEING PUSHED INLAND BY NORTHWEST WINDS. MVFR SHOULD TRANSITION
TO IFR THIS EVENING AS CEILINGS LOWER. INLAND MENDOCINO COUNTY...VFR
WILL PREVAIL THIS EVENING. STRATUS MAY MOVE OVER SOME OF THE
VALLEYS, BRINGING MVFR. INLAND ELSEWHERE...SMOKE/HAZE AROUND
MULTIPLE LARGE FIRES WILL BRING PARTIAL VISIBILITY REDUCTIONS.


&&

.MARINE...BROAD LOW PRESSURE AND LOOSE GRADIENTS WILL REMAIN OVER
THE AREA TONIGHT. HIGH PRESSURE OVER THE NE PACIFIC WILL START TO
BUILD EASTWARD TOWARD THE PACIFIC NW COAST BY EARLY TUE
MORNING...CREATING A TIGHTER PRESSURE GRADIENT OVER THE NORTHERN
OUTER WATERS. THE GFS...ECMWF AND NAM12 INDICATE NORTHERLY WINDS
REACHING 20KT IN THE NORTHERN 1/3RD OF PZZ470 BY TUE. THIS IS NOT
QUITE ADVISORY LEVEL...HOWEVER NORTHERLY WINDS WILL CONTINUE TO
INCREASE IN THE OUTER WATERS TUE NIGHT THROUGH WED. THE GFS
CONTINUES TO INDICATE LOW END GALES ON THU...WITH GUSTS TO 35-40KT
POSSIBLE OVER THE NORTHERN OUTER WATERS. IT IS STILL SEVERAL DAYS
OUT AND THE MODELS CAN CHANGE. CONFIDENCE IS HIGH WINDS WILL
INCREASE. THE EXACT MAGNITUDE IS STILL SKETCHY.

SEAS HAVE BEEN AROUND 3 FT AT 7 SECONDS TODAY. THE NWPS AND ENP SHOW
QUITE A MIX OF LONGER PERIOD WAVES ALL OF WHICH ARE FAIRLY
SMALL...ABOUT 1 FT OR LESS. THE DOMINATING WAVE GROUP HAS BEEN
CENTERED NEAR 8 SECONDS...SO WILL KEEP LEANING TOWARD THE SHORTER
PERIOD WAVES IN THE FORECAST. THE NWPS AND ENP HAS WIND DRIVEN WAVES
REACHING 5 TO 7 FT AT 7 SECONDS BY MID MORNING TUE IN PZZ470. THE
SMALL CRAFT ADVISORY REMAINS UP FOR PZZ470 STARTING TUE MORNING.
WIND-DRIVEN SEAS SHOULD CONTINUE TO INCREASE EACH DAY THROUGH THU.
BASED ON OUR LOCAL 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 ARE FOLLOWING THE NWPS GUIDANCE
WHICH HAS SEAS REACHING 13 FT ON THU IN PZZ470. THE ENP WAS A COUPLE
OF FEET LESS...BUT STILL NEAR CRITERIA.


&&

.FIRE WEATHER...A SERIES OF TWO UPPER LEVEL WAVES MAY TRIGGER
ISOLATED STORMS OVER INTERIOR NORTHWEST CALIFORNIA THIS
AFTERNOON/EVENING AND THEN AGAIN TUESDAY AFTERNOON/EVENING. ANY
DEVELOPMENT WILL LIKELY BE LIMITED SO ONLY A HEADLINE WILL BE
INCLUDED IN THE FIRE WEATHER FORECAST THROUGH TUESDAY. A BETTER
CHANCE FOR STORMS WILL RETURN THURSDAY NIGHT THROUGH SATURDAY AS AN
UPPER LEVEL LOW SLIDES THROUGH CENTRAL CALIFORNIA. THE BEST CHANCES
FOR STORMS WILL BE OVER MENDOCINO...SOUTHERN HUMBOLDT...AND TRINITY
COUNTIES WITH THE LOW MOVING INLAND WELL SOUTH OF THE AREA.
CONFIDENCE IS STILL LOW IN THE NUMBER OF STORMS EXPECTED AT THIS TIME
...BUT THERE IS THE POTENTIAL THAT STORMS COULD BECOME SCATTERED AND
FIRE WEATHER WATCHES/WARNINGS COULD BE REQUIRED.

THE MARINE LAYER PUSHED WELL INLAND LAST NIGHT AND SHOULD REACH
SIMILAR LOCATIONS THE NEXT TWO NIGHTS AS THE UPPER LEVEL WAVES MOVE
OVERHEAD. A RIDGE WEDNESDAY AND THURSDAY WILL LIKELY COMPACT THE
MARINE LAYER SLIGHTLY RESTRICTING INLAND PENETRATION OF THE COASTAL
CLOUDS. THUS OVERNIGHT RH RECOVERIES WILL BE GENERALLY GOOD THE NEXT
TWO NIGHTS AND THEN BEGIN TO DECREASE WEDNESDAY NIGHT. RPA


&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY FROM 8 AM TUESDAY TO 5 PM PDT FRIDAY FOR
     PZZ470.

&&

$$

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