Weather Service Report


297 
FXUS66 KEKA 172354
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
354 PM PST WED DEC 17 2014

.SYNOPSIS...PERSISTING RAIN SHOWERS WILL DIMINISH OVERNIGHT. THEN
BUILDING HIGH PRESSURE WILL RESULT IN A MOSTLY DRY DAY ON
THURSDAY. AN APPROACHING COLD FRONT WILL BRING THE NEXT
OPPORTUNITY FOR RAIN LATE THURSDAY NIGHT THROUGH FRIDAY MORNING. 

&&

.SHORT TERM...(TODAY THRU THURSDAY) A WEAK DISTURBANCE HAS PROLONGED 
VERY LIGHT SHOWER ACTIVITY TODAY FOR MOSTLY AREAS NORTH OF CAPE 
MENDOCINO. THE 23Z RADAR IMAGERY SHOWS LIGHT TO MODERATE RAIN 
OFFSHORE MAKING ITS WAY ONSHORE. THE APPROACHING SURFACE LOW WILL
BRING ONE LAST SHOT OF RAIN THIS EVENING AS IT SLIDES PAST THE NW
CALIFORNIA COAST. ADDITIONAL RAINFALL THROUGH TONIGHT WILL BE ON
THE LIGHTER SIDE AMOUNTING TO AROUND ONE QUARTER INCH. SNOWFALL
WITH THE LINGERING SHOWERS WILL NOT POSE A MAJOR CONCERN THIS
EVENING AS PRECIPITATION WILL BE LIGHT AND SNOW LEVELS ARE
FORECAST TO GRADUALLY INCREASE OVERNIGHT.

500MB HEIGHTS WILL GRADUALLY BUILD OVERNIGHT INTO THURSDAY AS A WEAK 
UPPER LEVEL RIDGE SHIFTS OVER THE WEST COAST OF THE UNITED STATES. 
THIS SHOULD RESULT IN MOSTLY DRY WEATHER EARLY IN THE DAY, HOWEVER, 
MOISTURE STREAMING OVER THE RIDGE COULD RESULT SOME LIGHT SPRINKLES 
THROUGH THE DAY. THEN, A BOUNDARY ASSOCIATED WITH AN UPPER LEVEL LOW 
LOCATED OFF OF THE COAST OF BRITISH COLUMBIA WILL APPROACH NORTHWEST 
CALIFORNIA THURSDAY EVENING. RECENT MODEL RUNS HAVE SPED UP THE 
ARRIVAL OF THE RAIN TO THURSDAY EVENING BUT STILL REMAIN IN DECENT 
AGREEMENT WITH ONE ANOTHER. RAINFALL CAN BE HEAVY AT TIMES WITH MOST 
AREAS LOOKING AT 0.75 INCHES OVERNIGHT AND HIGHER TERRAIN ACROSS 
FAVORABLE AREAS GETTING AS MUCH AS 1.5 INCHES. SNOWLEVELS WILL 
REMAIN AROUND 5000 FEET AS MOST OF THE PRECIPITATION FALLS BUT
WILL DECREASE INTO THE MORNING. FLURRIES MAY BE OBSERVED AT SOME
MOUNTAIN PASSES HOWEVER SNOWFALL SHOULD MOSTLY BE RESTRICTED TO
THE TRINITY ALPS WITH THE PASS ON HIGHWAY 3 SOUTH OF CALLAHAN
SEEING POTENTIAL IMPACTS.
 
.LONGTERM...(FRIDAY THRU WED) SHOWERS WILL DIMINISH FRIDAY RESULTING 
IN A MOSTLY DRY DAY HOWEVER THE WET PATTERN CONTINUES SATURDAY AND 
AGAIN SUNDAY AS FLOW BECOMES MORE ZONAL. THE LONGWAVE MODEL HINTS 
TOWARDS THE DEVELOPMENT OF A LONGWAVE RIDGE ACROSS THE WESTERN 
UNITED STATES THIS WEEKEND. I FEAR MODELS MAY POTENTIALLY BE OVER 
DOING THE PRECIPITATION FOR THIS WEEKEND BUT MADE LITTLE TO NO 
CHANGES DUE TO UNCERTAINTY. STRONGER RIDGING WILL BUILD OVER THE 
EASTERN PACIFIC EARLY NEXT WEEK BRINGING WARMER TEMPERATURES AND 
DRIER WEATHER THROUGH THE MIDDLE OF THE WEEK. BOTH THE GFS AND ECMWF 
HINT AT ANOTHER TROUGH FOR LATE NEXT WEEK BUT DIFFER IN THE 
STRENGTH. AGAIN FEW CHANGES WERE MADE TO THE LONG TERM AND CLIMO 
POPS WERE USED FOR THE TAIL END OF THE FORECAST. \KML

&&

.AVIATION...A WEAKENING LOW PRESSURE SYSTEM OFFSHORE WILL PROVIDE 
MORE PERIODS OF LIGHT TO MODERATE RAIN AS WELL AS OCCASIONAL MVFR 
CONDITIONS TONIGHT. LINGERING MOIST AIR WILL MAKE IFR CIGS AND VSBYS 
POSSIBLE AT UKIAH AND OTHER VALLEYS IN THE INTERIOR BY EARLY THU 
MORNING. CONDITIONS SHOULD IMPROVE TO VFR THROUGH THE DAY ON THU. 

&&

.MARINE...WINDS HAVE TURNED SOUTHERLY IN ADVANCE OF A WEAKENING LOW
APPROACHING THE WATERS. SHIP REPORTS SHOWED WINDS AROUND 15-20 KT 
WHICH SEEMED TO MATCH BETTER WITH THE GFS...HI-RES-NMM AND HRRR. THE 
SREF AND NAM12 LOOKED UNDERDONE. BOTH THE HIRES-NMM AND HRRR SHOW A 
RIBBON OF 20-25KT IN THE OUTER WATERS AND AROUND CAPE MENDO THROUGH 
THIS EVENING. ALSO SEAS HAVE BEEN RUNNING 2 TO 3 FT ABOVE THE MODEL 
GUIDANCE THROUGH THE DAY. MOST OF THIS WAVE ENERGY HAS BEEN COMING 
FROM 280-290 DEGREES. THUS EXTENDED THE SMALL CRAFT ADVISORY THROUGH 
TONIGHT. THE MODELS CONTINUE TO SHOW THE WESTERLY SWELL TRENDING 
DOWNWARD ON THURSDAY INTO THURSDAY NIGHT AS A STRONGER FRONTAL 
SYSTEM APPROACHES THE WATERS THROUGH THE DAY. SOUTHERLY WINDS WILL 
START TO RAMP BACK UP TO SMALL CRAFT LEVELS OF 20-25 KT BY THURSDAY 
EVENING. THE MODELS TEND TO BE TOO SLOW WITH WINDS INCREASING...SO 
THE ADVISORY HAS BEEN EXTENDED INTO THU AND THU NIGHT. THE FRONT 
WILL MOVE INLAND BY FRI MORNING LEAVING MUCH LIGHTER WINDS IN ITS 
WAKE.

A HURRICANE FORCE LOW CURRENTLY SOUTH OF THE ALEUTIAN ISLANDS WILL 
PRODUCE A LARGE SWELL WHICH WILL PROPAGATE TOWARD THE NORCAL COAST 
AND ARRIVE ON FRIDAY. ASCAT PASS SHOWED 50-55KT IN THE SOUTHERN HALF 
OF THE LOW. THIS AGREES QUITE WELL WITH THE WAVE WATCH III WINDS.   
CONFIDENCE IS INCREASING A LARGE WESTERLY SWELL WILL HIT THE 
NORTHERN CAL COAST ON FRI. THE EXACT MAGNITUDE OF THE SWELL WILL BE 
MUCH MORE CERTAIN WHEN THE SWELL GOES BY THE OFFSHORE BUOYS; BUOY #2 
250NM WEST OF BLANCO WHICH IS THE ONLY ONE LEFT. 

FOR NOW HAVE STAYED CLOSED TO THE MODEL GUIDANCE WHICH HAS THE SWELL 
PEAKING AROUND 17 TO 19 FT AT 18 SECONDS FRIDAY NIGHT. BREAKERS 
AROUND 25 FEET WILL BE POSSIBLE FRIDAY NIGHT. JASON-2 ALTIMETRY 
MEASUREMENTS THUS FAR HAS CAPTURED ONLY THE SIDES OF THE WAVE MAX. 
HOPEFULLY WE GET A PASS RIGHT OVER THE CENTER TO CONFIRM THE WAVE 
HEIGHTS IN THE NEXT 12 HOURS. A MARINE WEATHER STATEMENT HAS BEEN 
ISSUED TO CALL ATTENTION TO THIS LARGE SWELL EVENT WHICH SHOULD
PRODUCE HAZARDOUS SURF CONDITIONS.

IN ADDITION...FORERUNNERS WILL BRING A POTENTIAL FOR SNEAKER WAVES 
DURING THE DAY ON FRIDAY. LOOKING AT THE SEA STATE SPECTRUM THERE 
WILL BE ANOTHER WESTERLY WAVE GROUP PRESENT...8-10 FT AROUND 13 
SECONDS ON FRIDAY. THE SHORTER PERIOD SOUTHERLY WAVE GROUP SHOULD BE 
NEGLIGIBLE. CONFIDENCE IT NOT HIGH THAT ALL OF THE VARIABLES WILL 
COME TOGETHER HERE FOR THIS TO BE A HIGH END THREAT FOR SNEAKER 
WAVES. 

THE SWELL WILL SUBSIDE OVER THE WEEKEND. A WARM FRONT WILL APPROACH 
THE WATERS ON SATURDAY INTO SATURDAY NIGHT BRINGING ANOTHER PERIOD 
OF SMALL CRAFT ADVISORY SOUTHERLY WINDS.

&&

.COASTAL FLOOD...PERSISTENT SOUTHERLY WINDS CONTINUE TO KEEP WATER
LEVELS ABOVE THE ASTRONOMICAL TIDES BY 1 TO 2 FT. THE ASTRONOMICAL
TIDES ARE NEARLY 8 FT IN HUMBOLDT BAY ON SATURDAY AND 8.1 FT ON
SUNDAY. DEPENDING ON HOW PERSISTENT THE SOUTHERLY WINDS ARE...THIS
COULD CAUSE SOME COASTAL FLOODING IN THE LOW LYING AREAS AROUND
HUMBOLDT BAY. IN ADDITION, WITH THESE HIGH WATER LEVELS THE HIGH
SURF MAY PUSH WATER UP HIGHER IN EXPOSED COASTAL AREAS. MKK

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY UNTIL 3 PM PST THURSDAY FOR PZZ450-455.

     SMALL CRAFT ADVISORY UNTIL 3 PM PST FRIDAY FOR PZZ470-475.

&&

$$

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