411
FXUS66 KEKA 172148
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
248 PM PDT WED SEP 17 2025
SYNOPSIS
INLAND TEMPERTURES WILL COOLDOWN THURSDAY WITH THE
ARRIVAL OF CLOUDCOVER AND PRECIPITATION. THUNDERSTORM ACTIVITY IS
EXPECTED THURSDAY THROUGH SATURDAY. AFTER A SHORT PERIOD OF
DRYING, RAIN CHANCES INCREASE AGAIN EARLY NEXT WEEK.
KEY POINTS:
-TROPICAL MOISTURE WILL SURGE IN FROM THE SOUTH STARTING LATE TONIGHT
-ANY THUNDERSTORMS THAT FORM THURSDAY WOULD BE ON THE DRIER SIDE,
CAPABLE OF STRONG DOWNDRAFT WINDS, AND WOULD CREATE A FIRE
WEATHER THREAT.
-AS MOISTURE BECOMES BETTER ESTABLISHED FRIDAY, THE FIRE WEATHER
THREAT WILL EASE WHILE AN ISOLATED HYDROLOGICAL THREAT MAY
DEVELOP WITH THUNDERSTORM ACTIVITY.
DISCUSSION
CLINGY STRATUS DAMPENED SUNSHINE WARMTH ALONG THE
IMMEDIATE NORTH COAST WEDNESDAY AFTERNOON, WHILE THE INTERIOR
EXPERIENCED ABOVE AVERAGE TEMPERATURES ONCE AGAIN. THE PATTERN WILL
QUICKLY CHANGE OVERNIGHT AS A REMNANT TROPICAL SYSTEM STREAMS
MOISTURE AND CLOUDCOVER FROM THE SOUTH. CHANCES FOR SHOWERS INCREASE
FROM THE SOUTH TO NORTH EARLY THURSDAY. THE AMOUNT OF INSTABILITY
FOR THE INITIAL MOISTURE SURGE IS STILL IN QUESTION. THERE IS ALSO A
GOOD AMOUNT OF CONVECTIVE INHIBITION (CIN) SHOWING UP IN THE
SOUNDINGS. ISOLATED THUNDERSTORMS MAY STILL DEVELOP (10%) OVER
THE SOUTHERN REGIONS THROUGH LAKE AND MENDOCINO COUNTIES STARTING
THURSDAY. THERE WILL BE AN INITIAL FIRE WEATHER THREAT THURSDAY
WITH MUCH EVAPORATION OF PRECIPITATION LIKELY THROUGH THE DRIER
LOWER LEVELS. THIS WILL CREATE GUSTY AND ERRATIC OUTFLOW WINDS
AROUND THE CONVECTIVE SHOWERS, AND PARTICULARLY WITH THUNDERSTORMS
WHERE WINDS WOULD HAVE THE POTENTIAL TO GUST OVER 40 MPH.
THE SHOWER AND THUNDERSTORM ACTIVITY WILL SPREAD NORTHWARD LATE
THURSDAY AND FRIDAY. A SURFACE LOW WILL FORM OFF THE COAST THROUGH
THIS PERIOD, INCREASING FORCING AND DRAWING THE PRECIPITATION
ACTIVITY WESTWARD THROUGH THE COASTAL REGIONS. MODELS CONTINUE TO
BECOME MORE AGGRESSIVE WITH THIS WESTWARD PUSH, AND PRECIPITATION
CHANCES HAVE BEEN INCREASED OVER THE COAST. A STRAY THUNDERSTORM
CANNOT BE RULED OUT ALONG THE COAST AS WELL. INSTABILITY IS
GREATLY IN QUESTION FRIDAY AS THE SIGNIFICANT CLOUD SHIELD AND
ONGOING SHOWERS/LIGHT RAIN WILL INHIBIT DAYTIME HEATING. IF
TRINITY COUNTY AND PARTS OF THE SURROUNDING COUNTIES GET A GOOD
WINDOW OF SUNSHINE, THERE WILL BE A GREATER CHANCE FOR
THUNDERSTORMS, BUT THAT ASPECT OF THE FORECAST HAS THE GREATEST
UNCERTAINTY IN GENERAL.
THIS TROPICALLY SOURCED MOISTURE WILL YIELD ANOMALOUS PRECIPITAL
WATER VALUES OF 1 INCH UP TO 1.4 INCHES. STORM MOTION WILL BE
MODERATE TO SLOW AT TIMES. AFTER THE COLUMN SATURATES LATE THURSDAY
AND FRIDAY, THE CONVECTIVE SHOWERS AND THUNDERSTORMS WILL BE CAPABLE
OF LOCALIZED HEAVY RAINFALL AND POSSIBLE HYDROLOGICAL CONCERNS SUCH
AS MUDSLIDES. MODELS BEGIN PULLING THE MOISTURE OUT SATURDAY, EASING
THE HYDROLOGICAL THREAT. SATURDAY DOES APPEAR TO HAVE A GOOD CHANCE
FOR DIURNAL CLEARING AND SURFACE HEATING, AND THIS MAY BRING THE
GREATEST COVERAGE AND PROBABILITY (20+%) FOR INTERIOR
THUNDERSTORMS FOR MAINLY TRINITY COUNTY.
JJW
AVIATION
COASTAL STRATUS WILL HAS BEEN PERSISTENT
ALONG THE NORTH COAST THIS AFTERNOON. LIFR AND IFR CEILINGS MAY
BREAK OUT LATE TODAY INTO EARLY THIS EVENING, HOWEVER A NORTH WIND
SURGE WILL LIKELY REPLENISH THE SUPPLY OF COOL DAMP MARINE AIR
TRAPPED UNDERNEATH A STOUT INVERSION AND THE COASTAL TERRAIN. LIFR
CONDITIONS ARE HIGH;Y PROBABLE BY MID TO LATE EVENING AND OVERNIGHT
FOR ALL COASTAL TERMINALS. INLAND AREAS CAN EXPECT VFR CONDITIONS
THROUGH THE TAF PERIOD EXCEPT FOR LOW CLOUD INTRUSION INTO THE NORTH
COAST RIVER VALLEYS. MID AND HIGH LEVEL MOISTURE FROM THE REMNANTS
OF A TROPICAL DISTURBANCE WILL BEGIN TO INVADE SKIES FROM THE SOUTH
ON THURSDAY. CONVECTION AND HIGH BASED T-STORMS WILL BE POSSIBLE
WITH THE DAYTIME HEATING OVER THE INTERIOR TERRAIN ON THURSDAY.
MARINE
HIGH PRESSURE OFFSHORE INTERACTING WITH THE LOW PRESSURE
INLAND WILL DRASTICALLY ENHANCE THE PRESSURE GRADIENT CREATING
STRONG, GALE FORCE SUSTAINED WINDS WITH GUSTS OVER 45KTS POSSIBLE
OVER THE OUTER WATERS TONIGHT THROUGH THURSDAY NIGHT. WIND WAVES OF
15FT OR MORE ARE PROBABLE ACROSS THE NORTHERN WATERS AND SOUTHERN
OUTER WATERS.
MARINE HAZARD PRODUCTS HAVE BEEN ISSUED FOR ALL MARINE FORECAST
ZONES. GALE WARNINGS HAVE BEEN ISSUED FOR THE OUTER WATERS. INNER
WATER ZONES OUT 10NM CAN EXPECT NEAR GALE GUSTS WITH LARGE WIND
WAVES PROPAGATING INTO THE WATERS. OUTER WATER ZONES 10-60NM CAN BE
SUBJECT TO GALE FORCE WINDS SOUTH OF CAPE BLANCO AND CAPE MENDOCINO
AND LARGE, VERY STEEP, WIND WAVES WITH BLOWING SPRAY.
WINDS BEGIN TO EASE SLIGHTLY LATE THURSDAY NIGHT THROUGH FRIDAY
MORNING WITH WIND WAVES BEGINNING TO EASE FRIDAY AFTERNOON THROUGH
SATURDAY MORNING. THIS WEEKEND, A NW SWELL OF 5FT AROUND 12 SECONDS
IS EXPECTED WITH WINDS BETWEEN 10-20KTS ACROSS ALL THE WATERS.
GLOBAL DETERMINISTIC MODELS ARE NOT ALIGNED AS TO WHAT THE SYNOPTIC
SET UP WILL BE, YET CLUSTER ANALYSIS INDICATES RELATIVELY ZONAL FLOW
ALOFT WITH A CUTOFF LOW OFF THE COAST OF CENTRAL CA. THIS WILL KEEP
WINDS BREEZY, WIND WAVES MILD, AND THE NW SWELL DECAYING.
FIRE WEATHER
INLAND CONDITIONS REMAIN WARM AND DRY WEDNESDAY
AFTERNOON. NORTHEAST WINDS WILL BECOME BREEZY TONIGHT OVER THE
INTERIOR RIDGES OF DEL NORTE ZONE 203. THESE WINDS WILL PERSIST INTO
FRIDAY MORNING. A REMNANT TROPICAL SYSTEM WILL BEGIN PUSHING
MOISTURE IN FROM THE SOUTH LATE WEDNESDAY. SHOWERS WILL MOVE IN
THURSDAY WITH A SLIGHT CHANCE FOR THUNDERSTORMS (10-15%) FOR MAINLY
MENDOCINO, LAKE AND SOUTHERN TRINITY COUNTIES THROUGH THURSDAY
AFTERNOON. THESE INITIAL STORMS WOULD BE MORE DRY IN NATURE, BUT
CONFIDENCE IS LOW ON AVAILABLE INSTABILITY AT THAT TIME. CONVECTIVE
SHOWERS AND THUNDERSTORMS WILL BE CAPABLE OF GUSTY AND ERRATIC
WINDS, PARTICULARLY IN ANY THUNDERSTORM DEVELOPMENT. MOISTURE AND
INSTABILITY INCREASE LATE THURSDAY AND FRIDAY WHEN BETTER CONFIDENCE
FOR ISOLATED THUNDERSTORMS (15-20%) AND A POTENTIAL (45%) WETTING
RAINFALL FROM SHOWERS AND MORE RAIN PRODUCTIVE THUNDERSTORMS.
THUNDERSTORM FORMATION FRIDAY WILL BE SOMEWHAT DEPENDENT ON HOW MUCH
CLEARING CAN OCCUR THROUGH THE AFTERNOON. SATURDAY WILL HAVE A
GOOD CHANCE FOR DIURNAL CLEARING AND SURFACE HEATING, AND THIS MAY
BRING THE GREATEST COVERAGE AND PROBABILITY (20%) FOR INTERIOR
THUNDERSTORMS FOR MAINLY TRINITY COUNTY.
EKA WATCHES/WARNINGS/ADVISORIES
CA...
NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 5 AM PDT
THURSDAY FOR PZZ450.
HAZARDOUS SEAS WATCH FROM LATE TONIGHT THROUGH THURSDAY
EVENING FOR PZZ450.
SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 11 AM PDT
THURSDAY FOR PZZ455.
SMALL CRAFT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR PZZ470.
GALE WARNING FROM 8 PM THIS EVENING TO 3 AM PDT FRIDAY FOR
PZZ470.
SMALL CRAFT ADVISORY UNTIL 5 PM PDT THIS AFTERNOON FOR
PZZ475.
GALE WARNING FROM 5 PM THIS AFTERNOON TO 3 PM PDT THURSDAY
FOR PZZ475.
NOTE: THE FULL FORECAST DISCUSSION IS NOW REGULARLY ISSUED BETWEEN
10 AM/PM AND 1 PM/AM. ADDITIONAL UPDATES WILL BE ISSUED AS NEEDED.
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