AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
430 AM PDT FRI SEP 28 2018

.SYNOPSIS...TEMPERATURES WILL COOL ACROSS THE REGION DURING THE
REMAINDER OF THE WEEK AS A STORM SYSTEM APPROACHES FROM THE WEST.
SHOWERS AND A FEW THUNDERSTORMS WILL BE POSSIBLE DURING SATURDAY,
WITH ADDITIONAL SHOWERS OCCURRING SUNDAY INTO EARLY NEXT WEEK.
WARMER AND DRIER CONDITIONS WILL THEN DEVELOP DURING THE MIDDLE
OF NEXT WEEK.

&&

.DISCUSSION...AN UPPER LOW WAS POSITIONED 480 MILES WEST-SOUTHWEST
OF CAPE MENDOCINO EARLY FRIDAY MORNING. WEAK LOBES OF ASCENT
PRODUCING HIGH LEVEL CLOUDINESS WERE ROTATING AROUND THE
LOW...OTHERWISE, IMPACTS FOR THE TIME BEING ARE NEGLIGIBLE. THIS
WILL CHANGE DURING SATURDAY AS THE LOW MOVES ONSHORE OVER NWRN CA
AND SWRN OR. COOLING MIDLEVEL TEMPERATURES COMBINED WITH MODEST
SURFACE HEATING WILL AID IN DESTABILIZING THE ATMOSPHERE AND
INCREASE THE PROBABILITY OF SHOWERS AS MOISTURE AND ASCENT
INCREASE AHEAD OF THE LOW. IN ADDITION, FORECAST SOUNDINGS (MAINLY
THE GFS) SHOW CAPE AND EL TEMPERATURES WILL BE SUFFICIENT FOR
POSSIBLE THUNDERSTORM DEVELOPMENT OVER HUMBOLDT, TRINITY, AND DEL
NORTE COUNTIES.

SATURDAY`S UPPER LOW WILL DEPART THE REGION BY SUNDAY MORNING,
FOLLOWED BY SHORTWAVE RIDGING SUNDAY AFTERNOON THAT WILL AID IN
SHOWER DISSIPATION ACROSS THE REGION. HOWEVER, A SECOND UPPER LOW
IS FORECAST TO APPROACH THE CA COAST MONDAY AND TUESDAY. AT THIS
TIME, MODEL GUIDANCE IS IN GOOD AGREEMENT PROGRESSING THE LOW
ONSHORE ACROSS SRN CA. THAT STORM TRACK WILL REDUCE THE POTENTIAL
FOR SIGNIFICANT PRECIPITATION OVER NWRN CA. AFTER TUESDAY, UPPER-
LEVEL HEIGHTS BUILD OVER THE NERN PACIFIC DURING MID TO LATE NEXT
WEEK. NORTHWESTERLY FLOW ALOFT WILL SUBSEQUENTLY DEVELOP AND
INCREASE THE PROBABILITY FOR WARM/DRY LOW-LEVEL OFFSHORE WINDS.

&&

.AVIATION...MARINE FOG AND STRATUS CONTINUES TO PLAGUE LOW-LYING
COASTAL AREAS WITH LIFR CEILINGS AND VISIBILITIES EARLY FRIDAY
MORNING, INCLUDING AT BOTH ACV AND CEC. CEILINGS ARE EXPECTED TO
LIFT SLIGHTLY AND SCATTER OUT ALONG THE COAST SOMETIME IN THE LATE
MORNING THROUGH MID-AFTERNOON TIMEFRAME, LIKELY RESULTING IN AT
LEAST A FEW HOURS OF VFR CONDITIONS. DURING THE LATE AFTERNOON AND
EVENING HOURS, AN APPROACHING LOW PRESSURE SYSTEM WILL CAUSE THE
MARINE LAYER TO DEEPEN, AND THIS WILL CONTINUE STEADILY THROUGH
THE NIGHT. AS A RESULT, WHILE OVERCAST MARINE STRATUS WILL RETURN,
CEILINGS ARE EXPECTED TO LIFT SLIGHTLY AND CLOUD TOPS WILL DEEPEN
COMPARED TO WHAT HAS BEEN SEEN IN RECENT DAYS. AS A RESULT, DENSE
FOG WILL BE LESS PREVALENT AND CEILINGS ARE MORE LIKELY TO BE IN
THE IFR TO MVFR RANGE THROUGH THE NIGHT, WITH MORE IMPROVEMENT
EXPECTED TOMORROW MORNING. SOME LIGHT DRIZZLE WILL ALSO BE
POSSIBLE OVERNIGHT TONIGHT. /BRC

&&

.MARINE...VERY LIGHT SOUTHERLY WINDS WILL GRADUALLY INCREASE
THROUGH TODAY AND SATURDAY, PEAKING SATURDAY AFTERNOON AND EVENING
AT AROUND 15 TO 25 KT ACROSS MAINLY THE OUTER WATERS AND NEAR
CAPE MENDOCINO. THESE SOUTH WINDS WILL GENERALLY MAINTAIN THROUGH
LATE SUNDAY BEFORE WEAKENING SUBSTANTIALLY MONDAY. AS A RESULT,
STEEPER SOUTHERLY SEAS WILL GRADUALLY BUILD OVER THE WEEKEND,
ALTHOUGH SIGNIFICANT WAVE HEIGHTS ARE EXPECTED TO REMAIN AT OR
BELOW 8 FEET DURING THIS TIME FRAME. GIVEN THE EXPECTED SOUTH TO
SOUTH-SOUTHEAST WIND DIRECTION, THE WORST CONDITIONS ARE EXPECTED
TO OCCUR ACROSS OFFSHORE AREAS, WITH SOME SHELTERING EXPECTED IN
NEARSHORE AREAS ALONG THE HUMBOLDT AND DEL NORTE COASTLINES.

ON MONDAY AND TUESDAY, WINDS WILL GRADUALLY SWITCH BACK FROM
SOUTHERLY TO NORTHERLY AND WEAKEN, ALLOWING STEEPER SOUTHERLY SEAS
TO SETTLE. HOWEVER, A LARGER LONG-PERIOD SOUTHERLY SWELL
ORIGINATING FROM HURRICANE ROSA WILL BEGIN TO PROPAGATE THROUGH
THE WATERS ON THESE TWO DAYS, IMPACTING PRIMARILY THE OUTER WATERS
AND WATERS SOUTH OF CAPE MENDOCINO. DUE TO THE EXPECTED WEAK
WINDS DURING THIS TIME FRAME, AND THE SHELTERING FROM THE SOUTH
SWELL PROVIDED FROM CAPE MENDOCINO, OCEAN CONDITIONS ARE EXPECTED
TO BE QUITE TRANQUIL ALONG THE HUMBOLDT AND DEL NORTE COASTLINES
MONDAY AND TUESDAY.

NORTH WINDS ARE EXPECTED TO STEADILY INCREASE THROUGH THE END OF
THE WORK WEEK, GENERATING STEEPER SEAS AND WORSENING OCEAN
CONDITIONS. /BRC

&&

.FIRE WEATHER...NORTHWEST CALIFORNIA WILL EXPERIENCE A COOLING
TREND DURING THE REMAINDER OF THE WEEK. MILD AFTERNOON
TEMPERATURES IN THE 70S AND 80S ARE EXPECTED DURING FRIDAY ACROSS
THE INTERIOR. THIS WILL BE FOLLOWED BY TEMPERATURES IN THE 60S AND
70S SATURDAY AND SUNDAY, WHICH WILL RESULT IN MUCH IMPROVED RH
VALUES ACROSS THE REGION. IN ADDITION, SHOWERS AND A FEW
THUNDERSTORMS WILL BE POSSIBLE DURING SATURDAY, WITH ADDITIONAL
SHOWERS EXPECTED SUNDAY INTO EARLY NEXT WEEK. IN THE EXTENDED
RANGE, GUSTY EAST-NORTHEAST WINDS ACCOMPANIED BY A WARM DRY
AIRMASS WILL BE POSSIBLE NEXT FRIDAY AND SATURDAY, WHICH COULD
YIELD ELEVATED FIRE WEATHER CONDITIONS IF FUELS REMAIN
SUFFICIENTLY DRY AFTER THIS WEEKENDS RAIN EVENT.

&&

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