Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 052214 CCA
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
314 PM PDT THU MAY 5 2016

.SYNOPSIS...AN UPPER LEVEL LOW WILL BRING A CHANCE OF SHOWERS AND
THUNDERSTORMS THROUGH FRIDAY. THE THREAT FOR STORMS WILL SHIFT
INTO TRINITY COUNTY AND EASTERN MENDOCINO COUNTY ON SATURDAY.

&&

.DISCUSSION...A BROAD UPPER LEVEL LOW WILL CONTINUE TO BRING
A CHANCE OF SHOWERS AND THUNDERSTORMS TO MOST OF NORTHWESTERN
CALIFORNIA THROUGH FRIDAY. STORMS HAVE BEEN FIRING UP OVER THE
INTERIOR ONCE AGAIN TODAY WITH DAYTIME HEATING. THE STORMS HAVE
BEEN GENERATING LOCALLY HEAVY RAIN AND PERHAPS HAIL. FOR THE MOST
PART THE CONVECTION WILL DIE DOWN TONIGHT WITH THE LOSS OF DAYTIME
HEATING...HOWEVER WITH HARD TO TIME AND IDENTIFY DISTURBANCES
PIN-WHEELING AROUND THE LOW...ISOLATED THUNDERSTORMS MAY SPARK
UP DURING THE LATE NIGHT AND EARLY MORNING HOURS THROUGH FRIDAY
EVEN OUT OVER THE COAST. CONFIDENCE HERE IS NOT VERY HIGH AS THE
MODELS CONTINUE TO INDICATE A RATHER HARSH ENVIRONMENT FOR
THUNDERSTORMS TO SURVIVE NEAR OR OVER THE MARINE LAYER. IT CERTAINLY
SEEMS POSSIBLE WITH THE FAIRLY MOIST MID LEVEL NORTHEASTERLY FLOW.

THE MAIN THREAT OF THUNDERSTORMS ON FRIDAY WILL BE DURING PEAK
HEATING IN THE INTERIOR WITH BOTH THE NAM12 AND GFS INDICATING
LIFTED INDICES AROUND -2C TO -4C AND MUCAPES IN EXCESS OF
1000J/KG. MAIN THREAT WILL BE CLOUD-TO-GROUND LIGHTENING
STRIKES...SMALL HAIL AND LOCALLY HEAVY RAINFALL. WRAP AROUND
MOISTURE IN THE NORTHEASTERLY FLOW AND INSTABILITY WILL BE
SUFFICIENT FOR THUNDERSTORMS TO SPARK UP AGAIN WITH THE DAYTIME
HEATING IN TRINITY AND PERHAPS PORTIONS OF MENDOCINO COUNTY AGAIN ON
SAT. THE CONEVTIVE ACTIVITY SHOULD BE WEAKER ON SAT. AN UPPER RIDGE
WILL START TO EDGE CLOSER TO THE WEST COAST ON SAT AND THE AIR ALOFT
WILL WARM UP. THE THREAT FOR STORMS WILL START TO DECREASE BY
SATURDAY NIGHT AS THE AIR ALOFT WARMS AND LAPSE RATES LEVEL OFF. IT
IS STILL TOO EARLY TO RULE OUT ANY THUNDER CHANCES ESPECIALLY IN
EASTERN TRINITY WHERE THE MODELS CONTINUE TO DEPICT THE GREATEST
INSTABILITY.

UPPER LEVEL RIDGING WILL BUILD BY SUNDAY AND TEMPERATURES ALOFT WILL
WARM UP MORE SUBSTANTIALLY. WARMER AND SUNNIER CONDITIONS ARE
EXPECTED ON SUNDAY ACROSS THE INTERIOR FOR THE MOST PART. THE MODELS
STILL INDICATE SOME POTENTIAL FOR ISOLATED SHOWERS OVER THE HIGHER
ELEVATIONS OF TRINITY COUNTY THOUGH. ALSO A WEAK FRONT IN THE
NORTHWEST FLOW MAY GENERATE SOME DRIZZLE AND PERHAPS FOG SAT NIGHT
ALONG THE NORTH COAST...OTHERWISE DRY AND STABLE CONDITIONS SHOULD
PREVAIL ON SUNDAY.

UPPER LEVEL RIDGING OFFSHORE WILL LIKELY DOMINATE MON THROUGH WED OF
NEXT WEEK PROVIDING DRIER AND SUNNIER WEATHER CONDITIONS AS WELL AS
WARMER TEMPERATURES IN THE INTERIOR. THE SURFACE FLOW PATTERN WILL
BE FAVORABLE FOR STRATUS AND FOG WITH NEAR NORMAL TEMPERATURES AT
THE COAST...HOWEVER. MODELS INDICATE ANOTHER UPPER LOW AND
UNDERCUTTING FLOW LATE NEXT WEEK...BUT DIVERGE ON THE EASTWARD
PROGRESSION AND WHERE THE CLOSED LOW WILL FORM. BOTH THE GFS AND
ECMWF KEEP THE LOW FAR ENOUGH AWAY ON THU AND FOR NOW WILL NOT
ADD ANY MENTION OF SHOWERS OR CONVECTION TO THE FORECAST.

&&

.AVIATION...MVFR TO IFR CONDITIONS WILL LIKELY RETURN TO THE
COASTAL TERMINALS TONIGHT. MVFR CONDITIONS WILL MOST LIKELY
REDEVELOP AT UKIAH OVERNIGHT AS WELL. CONVECTION THIS AFTERNOON WILL
SLOWLY DIE DOWN THIS EVENING BUT MORE SHOWERS AND STORMS COULD FIRE
UP LATE TONIGHT. EXPECT IFR CONDITIONS TO DEVELOP IN THE INTERIOR
VALLEYS LATER TONIGHT.

&&

.MARINE...A STRONG OFFSHORE HIGH PRESSURE RIDGE INTERACTING WITH
AN INLAND LOW PRESSURE SYSTEM WILL MAINTAIN A TIGHT PRESSURE
GRADIENT AND ELEVATED WINDS AND SEAS ACROSS THE WATERS THE NEXT
FEW DAYS. SMALL CRAFT ADVISORIES WILL CONTINUE ACROSS THE NORTHERN
NEAR SHORE WATERS THROUGH EARLY SATURDAY MORNING AND ACROSS THE
SOUTHERN OUTER WATERS THROUGH FRIDAY NIGHT DUE TO ELEVATED WINDS
AND/OR SEAS. A HAZARDOUS SEAS WARNING WILL CONTINUE ACROSS THE
SOUTHERN OUTER WATERS THROUGH EARLY SATURDAY MORNING DUE TO
ELEVATED SHORT PERIOD SEAS. A GALE WARNING WILL CONTINUE ACROSS
THE NORTHERN OUTER WATERS THROUGH EARLY SATURDAY MORNING DUE TO
WIND GUSTS UP TO GALE FORCE OCCURRING. THE SEAS WILL DIMINISH THIS
WEEKEND DUE TO THE COMBINATION OF THE HIGH PRESSURE RIDGE
WEAKENING AND THE INLAND LOW PRESSURE SYSTEM PROPAGATING EASTWARD
ACROSS THE CENTRAL UNITED STATES. A WEAK COLD FRONT WILL APPROACH
THE REGION THIS WEEKEND.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY UNTIL 11 AM PDT SATURDAY FOR PZZ450.

     GALE WARNING UNTIL 11 PM PDT FRIDAY FOR PZZ470.

     SMALL CRAFT ADVISORY UNTIL 3 AM PDT SATURDAY FOR PZZ475.

     HAZARDOUS SEAS WARNING UNTIL 3 AM PDT SATURDAY FOR PZZ475.

&&

$$

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