987  
FXUS66 KEKA 312349  
AFDEKA  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE EUREKA CA  
349 PM PST SAT JAN 31 2015  
   
SYNOPSIS
 
 
DRY WEATHER WILL CONTINUE THROUGH AT LEAST SUNDAY IN MOST  
AREAS...BUT A WEAKENING UPPER RIDGE AND SEVERAL APPROACHING  
SYSTEMS ARE EXPECTED TO BRING LIGHT TO MODERATE RAINFALL TO AREAS  
NORTH OF CAPE MENDOCINO LATE SUNDAY THROUGH LATE TUESDAY. DRY  
WEATHER WILL RETURN BRIEFLY ON WEDNESDAY...FOLLOWED BY ANOTHER WET  
PATTERN LATE IN THE WEEK.  
 

 
   
SHORT TERM...THROUGH MONDAY
 
 
BENIGN WEATHER IS EXPECTED TO CONTINUE THROUGH THE DAY TOMORROW...BUT  
BIG CHANGES ARE ON THE WAY THROUGH THE REMAINDER OF THE WEEK AS  
SEVERAL STORM SYSTEMS WILL MOVE INTO THE PACIFIC NORTHWEST ALONG  
THE PERIPHERY OF A SLOWLY WEAKENING UPPER RIDGE. IN THE IMMEDIATE  
FUTURE...ANOTHER ROUND OF FOG CAN BE EXPECTED IN THE INTERIOR  
VALLEYS AND ALONG THE REDWOOD COAST...ALTHOUGH ITS EXTENT MAY BE  
SOMEWHAT LIMITED BY THE APPROACH OF BUILDING HIGH CLOUDS  
ASSOCIATED WITH THE FIRST IN A SERIES OF APPROACHING SHORTWAVES.  
WHILE PARTS OF DEL NORTE AND PERHAPS EXTREME NORTHERN HUMBOLDT  
COUNTY MAY BE ABLE TO SQUEEZE SOME RAIN OUT OF THIS INITIAL SYSTEM  
EARLY SUNDAY...THE STRENGTH OF THE AMBIENT UPPER RIDGE IS EXPECTED  
TO PRECLUDE ANY SIGNIFICANT ACCUMULATIONS UNTIL THE ARRIVAL OF A  
SLIGHTLY STRONGER SHORTWAVE AND A WEAK FRONT SOMETIME EARLY  
MONDAY. AT THIS POINT...DEEPER MOISTURE AND A SLIGHTLY WEAKER  
UPPER RIDGE WILL LIKELY ALLOW FOR A PERIOD OF MODERATE RAINFALL  
ACROSS PRIMARILY DEL NORTE...NORTHWESTERN TRINITY...AND NORTHERN  
HUMBOLDT COUNTIES...WITH A BIT MORE UNCERTAINTY FROM CENTRAL  
HUMBOLDT COUNTY SOUTHWARD. MODEL GUIDANCE IS RELATIVELY UNIFORM IN  
KEEPING THE BULK OF SIGNIFICANT ACCUMULATIONS WELL NORTH OF CAPE  
MENDOCINO...AND GIVEN THE AFOREMENTIONED STUBBORN UPPER RIDGE THIS  
SEEMS REASONABLE. IN ANY CASE...RAIN RATES ARE NOT EXPECTED TO BE  
HIGH ENOUGH TO RESULT IN ANY FLOODING CONCERNS EVEN IN THE WETTEST  
AREAS.  
   
LONG TERM...MONDAY NIGHT THROUGH SUNDAY
 
 
TWO SMALL SHORTWAVES WILL ADVANCE TOWARD NORTHWEST CALIFORNIA  
MONDAY EVENING THROUGH TUESDAY BRINGING PERIODS OF RAIN FOR MOST  
AREAS NORTH OF MENDOCINO COUNTY. THE ECMWF IS DRIER AND FARTHER  
NORTH WITH EACH SHORTWAVE THAN THE GFS AND NAM MODELS...BUT IN  
GENERAL AT LEAST SOME ACCUMULATING RAIN IS EXPECTED NORTH OF THE  
CAPE THROUGH EARLY TUESDAY AFTERNOON. AS SUCH...CHANCES FOR  
PRECIPITATION HAVE BEEN INCREASED WITH THIS UPDATE NORTH OF THE  
CAPE AND PARTICULARLY IN DEL NORTE COUNTY.  
 
THE LAST SHORTWAVE WILL BE ACCOMPANIED BY A WARM FRONT WHICH WILL  
SHIFT NORTH INTO OREGON LEAVING NORTHWEST CALIFORNIA IN THE WARM  
SECTOR OF A STRENGTHENING SYSTEM OFF THE WEST COAST. MODEL ENSEMBLE  
AND DETERMINISTIC RUNS ALL INDICATE A DEEP MOISTURE PLUME WILL MOVE  
INTO NORTHWEST CALIFORNIA LATE THURSDAY AND CONTINUE INTO THE  
WEEKEND AS UPPER LEVEL RIDGING BUILDS OVER THE INTER-MOUNTAIN WEST  
LEAVING SOUTHWEST FLOW AIMED AT THE NORTHERN HALF OF CALIFORNIA. THE  
WEST COAST ATMOSPHERIC RIVER LANDFALL TOOL INDICATES HIGH  
PROBABILITIES OF INTEGRATED VAPOR TRANSPORT (IVT) OVER 250 KG/M/S  
THURSDAY NIGHT THROUGH MONDAY AS THE MOISTURE PLUME UNDULATES NORTH  
AND SOUTH FROM SOUTHERN OREGON TO NORTH-CENTRAL CALIFORNIA. WITH THE  
PROLONGED PERIOD OF HIGH IVT IN THE GFS MODEL...THE MODEL IS  
PRODUCING WIDESPREAD HEAVY RAIN IN THE 6-12 INCH RANGE OVER THE  
REGION. THE CURRENTLY MORE CONSERVATIVE ECMWF ONLY INDICATES 3-7  
INCHES. THUS THERE IS HIGH UNCERTAINTY WITH THE RAINFALL AMOUNTS  
BUT NOT WITH WHETHER OR NOT IT IS GOING TO RAIN. POPS HAVE BEEN  
FURTHER INCREASED FRIDAY THROUGH SUNDAY AND IF MODEL TRENDS  
CONTINUE WILL BE INCREASED AGAIN WITH FUTURE UPDATES. IT SHOULD BE  
NOTED THAT THE WEATHER PATTERN DEPICTED IN THE MODELS IS A VERY  
FAVORABLE PATTERN FOR HEAVY RAINFALL IN NORTHWEST CALIFORNIA.  
 
GUSTY SOUTH WINDS ARE ALSO EXPECTED JUST AHEAD OF AND WITH THE HEAVY  
RAIN THURSDAY INTO FRIDAY. 925 MB WINDS ARE PREDICTED TO PEAK  
BETWEEN 40 AND 60 KT ALONG THE IMMEDIATE COAST WITH EVEN STRONGER  
WINDS FARTHER ALOFT IN THE GFS. IF THE GFS IS CORRECT WIND  
ADVISORIES OR WARNINGS MAY BE REQUIRED.  
 

 
   
AVIATION
 
 
VFR CONDITIONS WILL CONTINUE TO PREVAIL ACROSS THE REGION THROUGH  
TONIGHT. SOME OF THE INTERIOR RIVER VALLEYS WILL STILL SEE FOG AND  
LOW CLOUDS AS A RESULT OF THE LONG WAVE COOLING. KUKI MAY SEE SEE  
SOME BY DAYBREAK SUNDAY TOO. COASTAL SITES MAY SEE INTERLUDES OF  
MISTY HAZE THIS EVENING AS WINDS GO LIGHT AND SQUIRRELLY. HOWEVER  
WIND FIELDS WILL FAVOR A LIGHT OFFSHORE DIRECTION WHICH WILL  
HINDER MISTY AIR AND LOW CLOUD DEVELOPMENT. HIGH AND MID CLOUDS  
WILL SPREAD OVER THE REGION ON SUNDAY. CROSS SECTIONS INDICATE  
INCREASING ONSHORE FLOW AND LOWER LEVEL RH THROUGH THE DAY ON  
SUNDAY AS A WEAKENING FRONT APPROACHES FROM THE NW. THIS MAY  
RESULT IN MVFR CLOUD DECKS AT KCEC AND KACV...THOUGH EXACTLY WHEN  
AND HOW LOW ARE UNCERTAIN. GOING INTO SUNDAY NIGHT THE LOWER  
LEVELS WILL CONTINUE TO MOISTEN UP WHICH SHOULD EVENTUALLY RESULT  
IN IFR AT KACV AND KCEC.  
 

 
   
MARINE
 
 
GOING FORECAST LOOKED TO BE IN GOOD SHAPE AND ON TRACK THROUGH  
MID WEEK. NO CHANGES WERE NECESSARY. THE PRESS GRADIENT BETWEEN AN  
OFFSHORE RIDGE AND A THERMAL TROUGH ACROSS CALIFORNIA WILL  
GRADUALLY WEAKEN THE NEXT FEW DAYS. AS A RESULT...NORTH WINDS AND  
SHORT PERIOD SEAS WILL DIMINISH. SEAS WILL INCREASE EARLY NEXT  
WEEK AS A LONG PERIOD WESTERLY SWELL TRAVERSES THE WATERS. THE  
LONG PERIOD SWELL MAY RESULT IN GREATER RUN UP ON THE BEACHES;  
I.E. SNEAKER WAVES. NOT REAL CONFIDENT IN THIS AS THE SNEAKER WAVE  
INDEX INDICATES A LOW THREAT WITH THE SWELL BUILDING TO 8 FT  
AROUND 15 SECONDS BY MONDAY AFTERNOON. A PERIOD INCREASE OF JUST A  
FEW SECONDS WOULD PUT US IN A MODERATE RISK. THE NWPS AND ENP  
MODELS INDICATE NO SHORTER PERIOD WAVE GROUPS WHICH MAY NOT BE  
INCORRECT. THE WINDS WILL BE LIGHT SOUTHERLY EARLY NEXT WEEK AND  
PERHAPS SHORT PERIOD WIND WAVES WILL NEED TO BE ADDED INTO THE  
FORECAST. SOUTHERLY AND SOUTHEASTERLY WINDS WILL LIKELY INCREASE  
SIGNIFICANTLY TOWARD THE LATTER PORTION OF THE WEEK. HOW MUCH AND  
HOW FAST ARE NOT CERTAIN. THE GFS MODEL HAS BEEN CONSISTENTLY  
SHOWING A FAIRLY STRONG SYSTEM APPROACHING THE WATERS, SO FOR NOW  
WILL STAY CLOSE TO THE AVERAGED GFS SFC WINDS WHICH INDICATE SSE  
WIND OF 30-40KT AND THE POTENTIAL FOR GUSTS TO 45 AND 50  
KT...MOSTLY IN THE OUTER WATERS. IF THE WIND FORECAST PANS  
OUT...SEAS WILL HIT 18-20 FT WITH PERIODS AROUND 10 SECONDS IN THE  
OUTER WATERS. IT IS STILL 5 DAYS OUT AND THERE IS A CHANCE ALL OF  
THE MODELS ARE COMPLETELY WRONG. STAY TUNED.  
 

 
   
EKA WATCHES/WARNINGS/ADVISORIES
 
 
CA...NONE.  
NORTHWEST CALIFORNIA COASTAL WATERS...NONE.  

 
 

 
 
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