Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 250354
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
854 PM PDT FRI OCT 24 2014

.SYNOPSIS...A STRONG COLD FRONT WILL BRING RAIN AND VERY GUSTY
WINDS TONIGHT MAINLY AFTER MIDNIGHT THROUGH SATURDAY MORNING. THIS
WILL BE FOLLOWED BY POST FRONTAL SHOWERS AND A THREAT OF
THUNDERSTORMS IN THE AFTERNOON AND OVERNIGHT. SHOWERS WILL
DIMINISH AND WINDS WILL BE FAIRLY LIGHT ON SUNDAY.


&&

.UPDATE...THE LATEST GUIDANCE INDICATES THAT NUMEROUS GUSTS IN
EXCESS OF 50 KT CAN BE EXPECTED IN THE OUTER COASTAL ZONES JUST
AHEAD OF AND WITH THE FRONTAL PASSAGE. THUS THE GALE WARNING HAS
BEEN UPGRADED TO A STORM WARNING IN BOTH OUTER WATER ZONES. WIND
GUSTS ARE ALREADY APPROACHING ADVISORY CRITERIA IN THE MOUNTAINS
WITH GUSTS TO 43 MPH AT KNEELAND AS OF 8 PM. THUS THE WIND
ADVISORY TIMING LOOKS DECENT...THOUGH MAY NEED TO BE STARTED A
COUPLE OF HOURS EARLY. THE OVERNIGHT SHIFT WILL HAVE TO EXAMINE
WHETHER AN UPGRADE TO A HIGH WIND WARNING IS REQUIRED FOR LAND
AREAS AS GREAT MIXING BEHIND THE FRONT MAY ALLOW GUSTS TO APPROACH
60 MPH ON THE COAST IF CONDITIONS ARE JUST RIGHT.

ADDITIONALLY...THE CONVECTIVE PARAMETERS AHEAD OF THE POST FRONTAL
TROUGH BEHIND THE FRONT ARE QUITE IMPRESSIVE FOR OUR AREA. LOW
LEVEL SHEAR IS DECENT WITH CURVED HODOGRAPHS. IN FACT...THE
ENVIRONMENT IS SUPPORTIVE OF LOW TOPPED SUPERCELLS. THUS THERE IS
A DISTINCT POSSIBILITY OF WATERSPOUTS WITH STRONG STORMS AHEAD OF
THE POST FRONTAL TROUGH. THE MOST LIKELY AREA WILL BE NEAR CAPE
MENDOCINO WHERE THE NATURAL CURVE OF THE COAST INCREASES WIND
SHEAR/SPIN. CONSIDERING STORMS WILL BE MOVING TOWARD THE COAST AND
THE ENVIRONMENT WILL BE JUST AS CONDUCIVE FOR STRONG STORMS OVER
LAND...A LANDFALLING WATERSPOUT IS POSSIBLE...BUT AS USUAL NOT
VERY LIKELY. ADDITIONALLY...STRONG WIND GUSTS WILL BE POSSIBLE
WITH THE STRONGER STORMS. RADAR TRENDS WILL HAVE TO BE MONITORED
CLOSELY ON SATURDAY. RPA

&&

.PREV DISCUSSION......ISSUED AT 312 PM PDT...

SHORT TERM(TONIGHT THROUGH MONDAY)...CURRENT WATER VAPOR IMAGERY
SHOWS AN AREA OF LOW PRESSURE AROUND 500 MILES WEST OF EUREKA. THE
ASSOCIATED WARM FRONT HAS MOVED NORTH OF THE AREA INTO OREGON THIS
AFTERNOON. SKIES HAVE MAINLY CLEARED ACROSS NORTHWEST CA AND
TEMPERATURES HAVE WARMED TO NEAR 70 ACROSS THE AREA. THE COLD
FRONT IS APPROACHING THE COAST...BUT REMAINS AROUND 300 MILES
OFFSHORE. WINDS AHEAD OF THE COLD FRONT HAVE ALREADY STARTED TO
INCREASE THIS AFTERNOON WITH GUSTS TO 20 MPH AT THE OFFICE IN
EUREKA.

TONIGHT AS THE FRONT APPROACHES THE WINDS AND RAIN INCREASE. RAIN
IS EXPECTED TO START AT THE COAST AROUND MIDNIGHT AND SPREAD
INLAND QUICKLY. AREAS OF HIGHER TERRAIN WILL SEE HEAVIER RAIN AND
IT WILL START FIRST...ESPECIALLY THE SOUTH SLOPES. WINDS WILL
INCREASE THROUGH THE NIGHT AS WELL. WINDS WILL PEAK AT THE COAST
EARLY IN THE MORNING WITH THE FRONTAL PASSAGE. WITH THE FRONTAL
PASSAGE THE GFS/NAM/ECMWF MODELS ARE SHOWING WINDS AT 850 MB
PEAKING AT 50 TO 60 KT AT THE COAST AND A BIT LESS INLAND. THIS
MIX TO THE SURFACE WELL WITH GUSTS AT THE COAST EXPECTED TO BE
AROUND 40 TO 50 MPH. GUSTS TO 50 TO 70 MPH ARE POSSIBLE OVER THE
HIGHER ELEVATIONS NEAR THE COAST. FARTHER INLAND GUSTS TO 50 MPH
ARE POSSIBLE OVER THE HIGHER TERRAIN AND ONLY 30 TO 35 MPH GUSTS
IN THE VALLEYS. WIND ADVISORY LOOKS TO BE ON TRACK.

BEHIND THE FRONT THERE MAY BE A BRIEF BREAK IN THE RAIN BEFORE
THE UPPER LEVEL TROUGH MOVES OVER THE AREA. THIS TROUGH IS FAIRLY
COLD ALOFT AND WILL CREATE SOME INSTABILITY IN THE LATE MORNING
AND AFTERNOON. THERE LOOKS TO BE ENOUGH INSTABILITY FOR
THUNDERSTORMS. THE BULK SHEAR LOOKS FAIRLY HIGH WITH 30 TO 40 KT
IN THE 0-6KM LAYER AND 10 TO 20 KT IN THE 0-1KM LAYER. THIS SHOULD
BE ENOUGH TO CREATE SOME LONGER LASTING STORMS. THERE IS SOME
CURVATURE IN THE 0-1KM SHEAR DURING THE LATE MORNING OR EARLY
AFTERNOON. THIS COULD LEAD TO AN ISOLATED VERY WEAK TORNADO OR
WATERSPOUT...BUT THIS THREAT REMAINS FAIRLY SMALL THE CAPE IS LESS
THAN 500 J/KG. WINDS WILL BE DIMINISHING IN THE AFTERNOON...BUT
THERE IS STILL THE POTENTIAL FOR SOME STRONGER WINDS ALOFT TO MIX
DOWN TO THE SURFACE. SPC DOES HAVE US IN A MARGINAL RISK (A
RECENTLY UPDATED WAY OF SAYING "SEE TEXT") FOR SEVERE STORMS.
THERE WILL LIKELY BE SOME HAIL WITH THESE STORMS...ALTHOUGH 500MB
TEMPERATURES LOOK TO ONLY BE AROUND -21C WHICH DOESNT MAKE IT COLD
ENOUGH FOR US TO RECEIVE COPIOUS AMOUNTS OF SMALL HAIL. SATURDAY
NIGHT SHOWERS WILL CONTINUE ALTHOUGH AS WE LOOSE DAYTIME HEATING
THEY WILL LIKELY WEAKEN. THERE MAY BE SECONDARY STRENGTHENING
AGAIN AROUND SUNRISE AS AN UPPER LEVEL JET STREAK MOVES OVERHEAD.

SUNDAY SHOWERS WILL DIMINISH THROUGH THE DAY AND WINDS WILL BE
FAIRLY LIGHT. TEMPERATURES WILL BE REMAIN FAIRLY COOL. SKIES WILL
CLEAR THROUGH THE DAY. SOME FOG IS POSSIBLE IN THE MENDOCINO
COUNTY VALLEYS...BUT ELSEWHERE WILL LIKELY SEE ENOUGH MIXING TO
KEEP FOG OUT. SUNDAY NIGHT  MKK

LONG TERM (TUESDAY THROUGH SATURDAY)...AFTER A BREAK FROM THE
PRECIPITATION ON MONDAY...THE WET PATTERN RETURNS FOR THE LAST
WEEK OF OCTOBER. THE NEXT FRONTAL SYSTEM WILL ARRIVE ON TUESDAY
AND WILL GENERATE RAIN FROM CAPE MENDOCINO NORTHWARD WITH LESSER
AMOUNTS SOUTH OF CAPE MENDOCINO. THE GFS AND ECMWF SYNOPTIC MODELS
DIVERGE ON WEDNESDAY AND THURSDAY AS THE FLOW AMPLIFIES AND
ANOTHER UPPER LEVEL TROUGH DEEPENS AND SLOWLY APPROACHES THE
COAST. WITH THIS DEEPENING TROUGH...A WEAK FRONTAL BOUNDARY
BECOMES STATIONARY OVER NORTHERN CALIFORNIA AND OREGON. THIS
BOUNDARY WILL GENERATE SHOWERS ON THESE TWO DAYS. THE UPPER LEVEL
TROUGH WILL APPROACH THE COAST FRIDAY NIGHT INTO SATURDAY BRINGING
ANOTHER ROUND OF SIGNIFICANT PRECIPITATION TO NORTHERN CALIFORNIA.

AVIATION...WIDESPREAD CLEARING TODAY AND BRIEF DRYING AS A WARM
FRONT...ASSOCIATED WITH A STRONG LOW WELL WEST OF CAPE
MENDOCINO...LIFTED NORTH AND OUT OF NORTHWEST CALIFORNIA. AREAS OF
FOG CONTINUED ACROSS SEVERAL INLAND VALLEYS OF MENDOCINO COUNTY.
LIRF TO IFR CONDITIONS PERSISTED OVER UKIAH UNTIL MIDDAY. A POTENT
COLD FRONT...ASSOCIATED WITH THE LOW WEST OF CALIFORNIA...WILL
APPROACH THE COAST LATE TONIGHT. THIS SYSTEM WILL BE ACCOMPANIED
BY STRONG SOUTHERLY WINDS AND SOME HEAVY RAINS. CIGS AND VIS MAY
LOWER AS THE COLD FRONT SPREADS ACROSS THE REGION OVERNIGHT. THE
ENERGY WITH THIS SYSTEM COULD CREATE SIGNIFICANT AVIATION HAZARDS
AT CEC AND ACV ON SATURDAY. PERIODS OF HEAVY RAIN...LOW
VIS/CIG...WIND SHEAR AND EVEN THE POSSIBILITY OF THUNDERSTORMS
WILL BE AIRPORT AND FLIGHT HAZARD THREATS. TA

MARINE...GALE FORCE WINDS ASSOCIATED WITH A POTENT LOW PRESSURE
SYSTEM WILL ARRIVE TONIGHT. THE STRONGEST WINDS ARE EXPECTED LATE
TONIGHT INTO SATURDAY MORNING WITH THE COLD FRONT. WIND GUSTS UP TO
50 KT ARE POSSIBLE LATE TONIGHT OR EARLY SATURDAY IN THE VICINITY OF
THE FRONT AND NEAR CAPE MENDOCINO. A POST FRONTAL TROUGH MAY ALSO
KICK UP THE WINDS SATURDAY AFTERNOON AS INSTABILITY INCREASES IN THE
COOLER AIR BEHIND THE FRONT. NWPS HAS SHORT PERIOD SEAS HITTING 17
TO 22 FT LATE TONIGHT INTO SATURDAY MORNING. GALE WARNINGS CONTINUE
FOR ALL THE MARINE ZONES. GALE FORCE WINDS SHOULD START LATE THIS
AFTERNOON IN THE OUTER WATERS AND THEN EXPAND INTO THE INNER WATERS
LATER TONIGHT.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...     WIND ADVISORY FROM 2 AM TO 5 PM PDT SATURDAY FOR CAZ001.

     WIND ADVISORY FROM 2 AM TO 2 PM PDT SATURDAY FOR CAZ002-076.

     WIND ADVISORY UNTIL 5 PM PDT SATURDAY FOR CAZ003.

     WIND ADVISORY FROM 2 AM TO 11 AM PDT SATURDAY FOR CAZ004.

NORTHWEST CALIFORNIA COASTAL WATERS...
     STORM WARNING FROM 2 AM TO 2 PM PDT SATURDAY FOR PZZ470.

     GALE WARNING UNTIL 2 AM PDT SATURDAY FOR PZZ470-475.

     STORM WARNING FROM 2 AM TO 11 AM PDT SATURDAY FOR PZZ475.

     SMALL CRAFT ADVISORY UNTIL 2 AM PDT SATURDAY FOR PZZ450-455.

     GALE WARNING FROM 2 AM TO 9 PM PDT SATURDAY FOR PZZ450-455.

&&

$$

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