Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 212231
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
331 PM PDT SUN SEP 21 2014

.SYNOPSIS...HIGH PRESSURE WILL CONTINUE TO BRING DRY CONDITIONS
AND SEASONABLE TEMPERATURES TO NORTHWEST CALIFORNIA THROUGH MONDAY.
EXPECT LOW CLOUDS AND FOG ALONG THE COAST DURING THE NIGHT AND
MORNING WITH PARTIAL CLEARING IN THE AFTERNOON. A TROUGH MOVING
TOWARD THE WEST COAST EARLY THIS WEEK WILL BRING COOLER
TEMPERATURES AND WIDESPREAD RAIN BY THE MIDDLE OF THE WEEK.

&&

.SHORT TERM...2145Z VISIBLE SATELLITE SHOWS CLOUDS ALONG MOST OF
THE IMMEDIATE COAST AND PARTLY SUNNY SKIES ELSEWHERE. THE CLOUDS
WILL THICKEN ALONG THE IMMEDIATE COAST EARLY THIS EVENING AND
OVERNIGHT. VISIBILITIES SHOULD DROP IN THESE LOCATIONS AS FOG
DEVELOPS. EXPECT PARTIAL CLEARING BY MONDAY AFTERNOON. OTHERWISE,
HIGH PRESSURE WILL CONTINUE TO BRING DRY CONDITIONS AND SEASONABLE
TEMPERATURES TO NORTHWEST CALIFORNIA THROUGH MONDAY. A PACIFIC
TROUGH WILL BEGIN TO MOVE OVER THE WEST COAST LATE MONDAY,
BRINGING COOLER TEMPERATURES AND SOME HIGH CLOUDS. A COLD FRONT
ASSOCIATED WITH THIS TROUGH WILL MOVE TOWARDS NORTHWEST
CALIFORNIA TUESDAY AND SLOWLY MOVE THROUGH ON WEDNESDAY. EXPECT
RAIN TO DEVELOP FROM NORTH TO SOUTH TUESDAY INTO WEDNESDAY, WITH
WEDNESDAY BEING THE MOST LIKELY DAY FOR RAIN. THERE IS STILL SOME
UNCERTAINTY OVER HOW MUCH RAIN WILL FALL WHERE, BUT CONFIDENCE IS
HIGH THAT WE WILL GET RAIN, SO RAISED THE POPS WITH THIS FORECAST.
THE RAIN WILL TRANSITION TO SHOWERS LATE WEDNESDAY, BEHIND THE
FRONT.

.LONG TERM (THU THROUGH SUN)...MODELS REMAIN IN GOOD AGREEMENT
DIRECTLY BEHIND THE COLD FRONT WITH RAIN TURNING TO SHOWERS.
SIGNIFICANT COOLING IS NOT EXPECTED BEHIND THIS FRONT AS HEIGHTS
WILL NOT FALL MUCH. HOWEVER, MODELS ARE HAVE SOME ISSUES AS THEY
MOVE TOWARD THE WEEKEND. BOTH THE EC AND GFS HAVE A POST FRONTAL
TROUGH MOVING THROUGH THE REGION THU INTO FRI WITH A FEW SHOWERS
POSSIBLE AS IT LIFTS OUT TOWARD THE NE. HOWEVER, THE EC KEEPS THE
UPPER TROUGH LINGERING AROUND CALIFORNIA THROUGH THE WEEKEND WHILE
THE GFS KEEPS THE TROUGH MARCHING OFF TO THE EAST. IT SEEMS AS
THOUGH MODELS ARE HAVING A TOUGH TIME RESOLVING WHAT IS HAPPENING
TO THE DOWNSTREAM RIDGE OVER THE EASTERN HALF OF THE NATION. AS
SUCH, HAVE LEFT A FEW POPS IN OVER THE EASTERN PORTIONS OF THE CWA
TO GIVE SOME CREDENCE TO THE EC WHILE NOT TOTALLY DISCOUNTING THE
GFS. THE GEFS MEAN IS VERY SIMILAR TO THE GFS DETERMINISTIC RUN.
TEMPS WERE DONE WITH AN ALLBLEND FORECAST TO TAKE INTO ACCOUNT
MODEL VARIATION AND THE ONGOING FORECAST. BFG

&&

.AVIATION...AT 2 PM LST...THE MARINE LAYER REMAIN QUITE EXTENSIVE
ALONG THE NORTH COAST. HOWEVER...SOME BREAKS WERE OCCURRING IN THE
MOSTLY OVERCAST LAYER. THIS ALLOWED MORE WARMING TO OCCUR
ESPECIALLY FROM SOUTHERN HUMBOLDT BAY TO THE ARCATA AIRPORT. CIGS
HAVE LIFTED TO NEAR 2000 FEET WITH FURTHER POCKETS OF CLEARING
THROUGH MID-AFTERNOON. THE MARINE LAYER WAS DEEP ENOUGH FOR
STRATUS TO PENETRATE THE NEAR COAST RANGE EAST OF FT BRAGG INTO
WILLITS WHILE STRATUS EXTENDED FROM SANTA ROSA THROUGH THE
ALEXANDER VALLEY INTO UKIAH. THE CIGS THERE DROPPED TO 200 FEET
(IFR/LIFR CONDITIONS). EXPECT STRATUS ABOUT 1000 FEET TO RETURN
INTO UKIAH AND WILLITS VALLEYS LATE OVERNIGHT. TA

&&

.MARINE...WINDS AND SEAS WILL CONTINUE TO EASE THIS EVENING INTO
MONDAY AS WEAK SURFACE HIGH PRESSURE BUILDS IN FROM THE SW. WINDS
ARE FORECAST TO REMAIN GENERALLY OUT OF THE SOUTH IN THE 5 TO 15
KT RANGE WITH EXCEPTION OF DIRECTLY AROUND CAPE MENDOCINO WHERE
WINDS MAY REACH AS HIGH AS 20 KT. A NW WAVE SYSTEM CONTINUES TO
FILTER THROUGH THE WATERS AROUND 5 FT AT 12 SECONDS. THIS TOO WILL
EASE OVERNIGHT, DROPPING TO AROUND 4 FT AT 11 SECONDS BY MONDAY.

THE MAIN CHANGE WILL BE ON TUES AS A FRONT APPROACHES THE REGION
FROM THE WEST. MODELS SEEM TO BE IN DECENT AGREEMENT WITH WINDS
INCREASING TO 15 TO 25 KT JUST AHEAD OF THE FRONT WITH LOCALLY
STRONG GUSTS. STEEP SOUTHERLY WAVES WILL ACCOMPANY THIS INCREASE
IN WINDS. TIMING VARIES A TOUCH FROM MODEL TO MODEL, BUT WINDS
SHOULD BEGIN THEIR INCREASE EARLY TUESDAY MORNING. THE OTHER
THREAT WILL BE BUILDING POST FRONT SWELL. MODELS INDICATE THIS
SWELL OUT RUNNING THE FRONT AND ARRIVING IN THE COASTAL WATERS
ABOUT THE SAME TIME AS THE HIGHEST WINDS BEGIN. HOWEVER, THE SWELL
WILL LINGER FOR A FEW DAYS AS IT SLOWLY DECAYS OUT. AT ITS PEAK,
THE SWELL IS EXPECTED TO REACH 11 TO 13 FT AT ABOUT 15 SECONDS.

THE OTHER PIECE OF THE PUZZLE WILL BE WHAT IS HAPPENING BEHIND
THE FRONT. WHILE SWELL WILL BEGIN TO DECAY, MODELS ARE HINTING AT
A POST FRONT TROUGH MOVING THROUGH THE WATERS WHICH COULD INCREASE
SOUTHERLY WINDS AND STEEP WAVES AGAIN. WE`LL BE WATCHING TO SEE
HOW MODELS HANDLE THIS IN THE COMING DAYS. BFG

&&

.EKA WATCHES/WARNINGS/ADVISORIES...

CA...NONE.

NORTHWEST CALIFORNIA COASTAL WATERS...NONE.

&&

$$

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