839
FXUS66 KEKA 090814
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
114 AM PDT SUN AUG 9 2026
KEY MESSAGES
* HIGH CONFIDENCE (85 TO 100 PERCENT PROBABILITY) IN AT LEAST
WIDESPREAD MODERATE HEAT RISK CONTINUING ACROSS INTERIOR VALLEYS
TODAY, WHERE MAXIMUM AFTERNOON TEMPERATURES WILL REACH 100 TO 108
DEGREES.
* LOCALIZED CRITICAL FIRE WEATHER POSSIBLE THIS WEEKEND DUE TO
STRONGER AFTERNOON VALLEY WINDS AND LOW RELATIVE HUMIDITY.
* THERE IS THE POTENTIAL FOR THUNDERSTORMS LATE NEXT WEEK OR OVER
THE WEEKEND IN THE INTERIOR.
* STRONG NORTHERLY WINDS WILL SUSTAIN STEEP, HAZARDOUS SEAS AND GALE-
FORCE GUSTS UP TO 40 KNOTS ACROSS OUTER WATERS THROUGH AT
LEAST MONDAY.
SYNOPSIS
AN EXPANSIVE UPPER-LEVEL HIGH, CENTERED OVER THE GREAT
BASIN WILL MAINTAIN HOT, DRY CONDITIONS ACROSS INTERIOR NORTHWEST
CALIFORNIA THROUGH EARLY WEEK. OFFSHORE, A SHARP CROSS-COAST ZONAL
PRESSURE GRADIENT BETWEEN EAST PACIFIC HIGH PRESSURE AND THE
INTERIOR THERMAL TROUGH WILL DRIVE GALE-FORCE NORTHERLY WINDS AND
STEEP WAVES. INLAND TEMPERATURES WILL BEGIN A SLIGHT 3 TO 6 DEGREE
COOLING TREND BY MID-TO-LATE WEEK AS THE UPPER RIDGE GRADUALLY
WEAKENS.
DISCUSSION
STRONG MID-LEVEL SUBSIDENCE BENEATH A GREAT BASIN
RIDGE DOMINATES REGIONAL ATMOSPHERIC STABILITY, KEEPING SKY COVER
CLEAR AND PROMOTING RAPID DAYTIME SURFACE HEATING ACROSS INLAND
VALLEYS. AT THE SURFACE, THE PERSISTENT ZONAL PRESSURE GRADIENT
BETWEEN THE EASTERN PACIFIC HIGH AND THE INTERIOR THERMAL TROUGH
CONTINUES TO GENERATE STRONG COASTAL NORTHERLIES WHILE COMPRESSING
THE MARINE BOUNDARY LAYER BELOW 800 FEET AGL ALONG THE IMMEDIATE
SHORELINE.
MODEL ENSEMBLE GUIDANCE INDICATES AROUND A 90-100 PERCENT
PROBABILITY OF MANY INTERIOR VALLEY TEMPERATURES RISING ABOVE 100
DEGREES THIS AFTERNOON. AFTERNOON RELATIVE HUMIDITY VALUES WILL DROP
TO 8–14 PERCENT ACROSS MUCH OR THE INTERIOR VALLEYS, MAINTAINING
LOCALIZED ELEVATED FIRE WEATHER CONCERNS. MID-LEVEL HEIGHT FALLS
EARLY NEXT WEEK WILL SUPPORT A GRADUAL COOLING TREND BY THURSDAY AS
A BROAD TROUGH APPROACHES THE PACIFIC NORTHWEST.
LATE IN THE WEEK WITH THE BROAD TROUGH APPROACHING THERE IS THE
POTENTIAL FOR THUNDERSTORMS. THE CURRENT NBM IS SHOWING A 10 TO 20
PERCENT CHANCE OF THUNDERSTORMS ACROSS TRINITY COUNTY AND
NORTHEASTERN MENDOCINO COUNTY ON FRIDAY WITH A SIMILAR POTENTIAL
ON SATURDAY. THE ENSEMBLE CLUSTERS SHOW SOME VARIATIONS ON HOW
MUCH MOISTURE THERE WILL BE, BUT THEY WILL LIKELY BE FAIRLY DRY.
IT IS STILL POSSIBLE THERE WILL NOT BE ENOUGH MOISTURE FOR
ANY THUNDERSTORMS AT ALL. THIS WILL NEED TO MONITORED AS IT GETS
CLOSER.
AVIATION
A SHALLOW MARINE LAYER COMPRESSED BELOW 1500 FEET AGL
WILL HELP PROMOTE A RETURN OF IFR TO LIFR CEILINGS ALONG THE
IMMEDIATE COAST THROUGH LATE MORNING, ALTHOUGH CONFIDENCE IS
WANING ON HOW MUCH OF A REBOUND THAT STRATUS WILL HAVE. BOUNDARY
LAYER SATURATION WILL FAVOR LOWER SURFACE VISIBILITIES TO 1 TO 3
STATUTE MILES AT KCEC AND KACV BEFORE DAYTIME MIXING RESTORES VFR
CONDITIONS GENERALLY BETWEEN 18Z AND 20Z. KUKI WILL REMAIN
PREVAILING VFR UNDER CLEAR SKIES, WITH AFTERNOON NORTHERLY GUSTS
REACHING 15 TO 18 KNOTS.
MARINE
A TIGHT ZONAL PRESSURE GRADIENT WILL MAINTAIN GALE-
FORCE NORTHERLIES ACROSS OUTER WATERS. GALE WARNINGS REMAIN ACTIVE
FOR THE NORTHERN OUTER WATERS AND SOUTHERN OUTER WATERS INTO MONDAY,
WHERE GUSTS TO 40 KNOTS AND STEEP SEAS OF 10 TO 12 FEET AT 8 TO 9
SECONDS WILL PERSIST DUE TO LOCALIZED CORNERING ACCELERATIONS
DOWNWIND OF CAPE MENDOCINO AND POINT ST. GEORGE. SMALL CRAFT
ADVISORIES REMAIN IN EFFECT FOR THE NORTHERN INNER WATERS AND
SOUTHERN INNER WATERS FOR GUSTS TO 30 KNOTS AND STEEP 7 TO 8 FOOT
SEAS. MAY NEED FURTHER EXTENSIONS OR UPGRADES TO HAZARD COVERAGE FOR
AT LEAST THE NORTHERN OUTER WATERS BEYOND MONDAY.
FIRE WEATHER
STRONG SUBSIDENCE UNDER THE GREAT BASIN UPPER
RIDGE WILL MAINTAIN HOT AND DRY CONDITIONS ACROSS INTERIOR VALLEYS
TODAY. ENSEMBLES INDICATE AN 85 TO 90 PERCENT PROBABILITY OF
MINIMUM AFTERNOON RELATIVE HUMIDITY VALUES FALLING INTO THE 8 TO
14 PERCENT RANGE ACROSS PARTS THE INTERIOR VALLEYS. EXPECT MANY
INTERIOR VALLEY HIGHS REACHING 101 TO 108°F.
THE ZONAL PRESSURE GRADIENT BETWEEN THE OFFSHORE EASTERN PACIFIC
HIGH AND THE INTERIOR THERMAL LOW WILL DRIVE GUSTY AFTERNOON BREEZES
THROUGH INTERIOR VALLEYS AND ACROSS EXPOSED RIDGES. MODEL GUIDANCE
SHOWS A PROBABILITY OF WEST-NORTHWEST WIND GUSTS REACHING 20 TO 25
MPH THROUGH AT LEAST SOME WIND-PRONE GAPS AND MOUNTAIN PASSES. POOR
NOCTURNAL RELATIVE HUMIDITY RECOVERY OF 20 TO 35 PERCENT ALONG SOME
MIDSLOPES AND RIDGES ABOVE THE SHALLOW MARINE INVERSION WILL
MAINTAIN ELEVATED FIRE WEATHER CONCERNS OVERNIGHT.
THERE IS THE POTENTIAL FOR DRY THUNDERSTORMS FRIDAY AND/OR
SATURDAY THIS WEEK. CONFIDENCE REMAINS LOW ON THE DETAILS OF HOW
MUCH MOISTURE AND THE EXACT LOCATION OF THE STORMS. THE CURRENT
NBM HAS A 10 TO 20 PERCENT CHANCE OF THUNDERSTORMS ACROSS TRINITY
COUNTY AND DOWN IN THE YOLLA BOLLAS.
COASTAL FLOODING
SEA LEVELS HAVE BACKED OFF SLIGHTLY AND ARE
CURRENTLY RUNNING 0.7 FT ABOVE THE PREDICTED TIDE LEVEL IN
HUMBOLDT BAY. TIDES WILL BECOME MORE AMPLIFIED EARLY NEXT WEEK
FOLLOWING THE NORMAL LUNAR CYCLE. THE PREDICTED TIDE AT THE NORTH
SPIT IS 7.95 FT MLLW AT 10:21 PM ON MONDAY THE 10TH AND THEN 7.99
FT MLLW AT 11:17 PM ON TUESDAY THE 11TH. IF THE TIDE INCREASES
JUST SLIGHTLY TO RUN AROUND 0.8 FT ABOVE PREDICTED, THIS COULD
RESULT IN MINOR COASTAL FLOODING AROUND HUMBOLDT BAY WITH MINOR
IMPACTS IN KING SALMON AND POSSIBLY A FEW OTHER LOCATIONS AROUND
THE BAY.
EKA WATCHES/WARNINGS/ADVISORIES
CA...
HEAT ADVISORY UNTIL 10 PM PDT THIS EVENING FOR CAZ108-
110>114-116>120.
NORTHWEST CALIFORNIA COASTAL WATERS...
SMALL CRAFT ADVISORY UNTIL 10 PM PDT THIS EVENING FOR
PZZ450-455.
GALE WARNING UNTIL 3 AM PDT TUESDAY FOR PZZ470.
GALE WARNING UNTIL 10 AM PDT MONDAY 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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