497
FXUS66 KEKA 291217
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
517 AM PDT TUE APR 29 2025
SYNOPSIS
A QUICK PASSING TROUGH WILL BRING INCREASED CLOUD COVER
AND A SLIGHT CHANCE FOR MOUNTAIN SHOWERS ON TUESDAY. DRY WEATHER
RETURNS ON WEDNESDAY WITH TEMPERATURES WARMING WELL ABOVE NORMAL
THROUGH THURSDAY.
DISCUSSION
COASTAL FOG DEVELOPED ALONG THE NORTH COAST AND ADJACENT
RIVER VALLEYS OVERNIGHT. INCREASING HIGH LEVEL CLOUD COVER IS
SPREADING THROUGH THE AREA AHEAD OF A WEAK UPPER SHORTWAVE.
SHALLOW ELEVATED INSTABILITY IS EXPECTED TO OCCUR ACROSS THE
EASTERN PORTION OF TRINITY AND AROUND THE YOLLA BOLLY THIS
AFTERNOON, BUT HI-RES MODELS SHOW LIMITED SHOWER ACTIVITY STAYING
MOSTLY EAST TOWARD THE INTERIOR VALLEY.
RIDGING WILL ONCE AGAIN BUILD BACK OVER THE WEST COAST ON WEDNESDAY
BRINGING WARM TEMPERATURES TO THE INTERIOR WITH HIGH TEMPS IN VALLEY
LOCATIONS EXCEEDING 80 DEGREES IN SOME LOCATIONS. AFTER MORNING
COASTAL STRATUS AND VALLEY FOG, ABUNDANT CLEAR SKIES ARE EXPECTED.
500MB PATTERN ON THURSDAY WILL RESEMBLE A REX BLOCK. A POSITIVE
HEIGHT ANOMALY WILL REMAIN CENTERED OVER THE PAC NW (WASHINGTON
AND OREGON) AND EXTEND SOUTHWARD INTO NORTHERN CALIFORNIA. A CUT-
BACK TROUGH OR CLOSED 500MB CYCLONIC CIRCULATION OFFSHORE OR OVER
CENTRAL/SOUTHERN CALIFORNIA WILL COMPLETE THE REX-BLOCK PATTERN.
IT IS POSSIBLE FOR WRAP AROUND MOISTURE FROM THE CLOSED LOW TO
SPREAD OVER LAKE AND EASTERN MENDOCINO FOR DIURNAL CONVECTION. ALL
6-HOURLY ENSEMBLE MEMBERS FROM THE ENS, GEFS AND CMCE INDICATE NO
PRECIP. ALSO, NBM PROBABILITIES FOR THUNDERSTORMS > 15% ARE WELL
TO THE EAST AND SOUTHEAST; OVER THE SIERRA NEVADA MTN RANGE.
INTERIOR HIGH TEMPERATURE WILL REMAIN ABOVE AVERAGE ON THU UNDER
LARGE SCALE ADIABATIC WARMING FROM THE RIDGE CENTERED OVER THE PAC
NW. HIGH TEMPS IN THE MID 70'S TO MID 80'S ARE GENERALLY
EXPECTED, HOWEVER A FEW HOT SPOTS SUCH BIG BAR RAWS WILL PROBABLY
EXCEED 90F. /ZVS/JMM
EXTENDED DISCUSSION...FRIDAY THROUGH SUNDAY
GET READY FOR MORE COOL AND WET WEATHER. A 500MB TROUGH WILL DIG
SOUTHWARD FROM THE GULF OF ALASKA AND APPROACH NW CAL ON FRIDAY.
ALL DETERMINISTIC MODELS, GFS, ECMWF, GDPS, ICON AS WELL AS
ENSEMBLE MEANS WERE IS GOOD AGREEMENT WITH DRIVING A FRONTAL
BOUNDARY ACROSS THE NORTHERN PORTION OF THE AREA ON FRIDAY.
24-HOUR ENSEMBLE CLUSTER MEANS CONTINUE TO DEPICT SUBTLE
DIFFERENCES WITH PLACEMENT, TIMING AND OVERALL EVOLUTION OF THE
COLD CORE ALOFT. BY 5AM SAT, OVER HALF AN INCH WILL BE POSSIBLE
(50% CHANCE) FOR INTERIOR DEL NORTE. NOT A MAJOR RAIN EVENT BY ANY
STRETCH BUT WET WEATHER WILL IMPACT OUTDOOR ACTIVITIES AND
PROJECTS. SPRING SNOWFALL WILL ALSO BE POSSIBLE ABOVE 4000-4500
FEET WITH 1 TO 2 INCHES OF STORM TOTAL ACCUMULATION BY 5 AM
SUNDAY.
INTERIOR TEMPERATURES WILL BE CONSIDERABLY COOLER AND WELL BELOW
NORMAL AGAIN NEXT WEEKEND (SAT MAY 3 AND SUN MAY 4). THERE MIGHT
EVEN BE POCKETS OF MORNING FROST IN THE INTERIOR VALLEYS WITH MIN
TEMPS BELOW 36F. PRECIP CHANCES GENERALLY DIMINISH AS WE HEAD INTO
SUNDAY AS THE TROUGH HEADS SOUTHWARD AND EASTWARD. /DB
AVIATION
A MARINE STRATUS LAYER REMAINS CONSISTENT OVER THE
HUMBOLDT COAST AND NEARSHORE RIVER VALLEYS AS THE MARINE LAYER
GROWS TO 2K FEET. STRONG NORTHERLY WINDS DECOUPLED OVERNIGHT AT
THE COASTAL TERMINALS, ALLOWING A SOUTHERLY FLOW REVERSAL TO
DEVELOP - STRATUS HAS FINALLY REACHED THE DEL NORTE COAST,
LEAVING CEC AND ACV IFR BENEATH OVERCAST CEILINGS. A WEAK
SHORTWAVE IS EXPECTED TO MOVE THROUGH THE NORCAL COAST LATE THIS
MORNING, DISTURBING THE MARINE LAYER AND LIKELY PRODUCING AT LEAST
MVFR CEILINGS AT BOTH COASTAL TERMINALS THROUGH EARLY AFTERNOON.
GUSTY NORTHERLY WINDS 15 TO 25 KNOTS ARE EXPECTED AFTER 21Z
FOLLOWING A WEAK SURFACE FRONTAL PASSAGE. VERY LIGHT DRIZZLE IS
POSSIBLE AT THE COAST LATE THIS EVENING. JMM
MARINE
HIGH PRESSURE OVER THE AREA IS EXPECTED TO BRING
NORTHERLY WINDS THROUGH WEDNESDAY. THURSDAY A WEATHER SYSTEM
APPROACHING THE AREA WILL DIMINISH THESE WINDS MORE. WINDS FRIDAY
WILL MAY BRIEFLY TURN SOUTHERLY AT LEAST IN THE NORTHERN WATERS.
SATURDAY AND SUNDAY NORTHERLY WINDS RETURN AND THEY MAY BE NEAR
GALE OR GALE FORCE AGAIN. WAVES WILL CONTINUE TO BE MAINLY WIND
DRIVEN THROUGH MUCH OF THE WEEK. FRIDAY A 16 SECOND SWELL IS
EXPECTED TO BUILD TO AROUND 4 OR 5 FEET. MKK/TRN
EKA WATCHES/WARNINGS/ADVISORIES
CA...
NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 9 PM PDT WEDNESDAY FOR PZZ450-
455-470-475.
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