Area Forecast Discussion
Issued by NWS Eureka, CA

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FXUS66 KEKA 310321
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
821 PM PDT WED JUL 30 2014

.SYNOPSIS...SHOWERS AND THUNDERSTORMS ARE TAPERING QUICKLY THIS
EVENING OVER TRINITY COUNTY. HOWEVER...AN UPPER SHORTWAVE TROUGH
APPROACHING FROM THE SW WILL CROSS NW CALIFORNIA OVERNIGHT
BRINGING A SLIGHT CHANCE OF DRY LIGHTNING OVER MENDOCINO COUNTY.
OTHERWISE...FAIR CONDITIONS WILL PREVAIL ACROSS THE INTERIOR WHILE
LOW CLOUDS AND FOG SETTLE IN ALONG THE COAST. MORE THUNDERSTORMS
ARE EXPECTED ACROSS EASTERN TRINITY COUNTY THURSDAY AFTERNOON.

&&

.UPDATE...THROUGH COORDINATION WITH THE USFS REDDING FIRE WEATHER
OFFICE, HAVE ADDED IN A SLIGHT CHANCE OF DRY LIGHTNING OVERNIGHT
TO MENDOCINO, FAR SOUTHERN TRINITY, AND EXTREME SE HUMBOLDT
COUNTIES. ANOTHER SHORTWAVE TROUGH, SIMILAR TO LAST NIGHT, IS
APPROACHING FROM THE SW THIS EVENING. WHILE NOT AS VIGOROUS AS THE
PREVIOUS NIGHT, THIS SHORTWAVE IS SHOWING ACCAS IN EVENING
SATELLITE IMAGERY GIVING ME JUST ENOUGH CONFIDENCE TO ADD DRY
THUNDERSTORMS TO THE FORECAST. THAT SAID, CONFIDENCE IS RATHER LOW
OF SOMETHING OCCURRING, BUT WOULD BE REMISS TO NOT HAVE DRY
LIGHTNING IN THE FORECAST. HAVE NOT ISSUED ANY FIRE WEATHER
WATCHES OR WARNING DUE TO THE LOW CONFIDENCE. THIS THREAT WILL END
AS THE WAVE PASSES OVERNIGHT.
OTHERWISE, THE FORECAST REMAINS ON TRACK. BFG

IF YOU WITNESS ANY LIGHTNING OVERNIGHT PLEASE LET US KNOW THROUGH
OUR SOCIAL MEDIA CONTACTS AT THE BOTTOM OF THIS DISCUSSION. IF YOU
SEE A WILDFIRE, PLEASE REPORT IT TO YOUR LOCAL FIRE AGENCY.

&&

.PREV DISCUSSION......ISSUED AT 340 PM PDT...

SYNOPSIS...ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED OVER
THE TRINITY ALPS THIS AFTERNOON AND EARLY EVENING. A SLIGHT CHANCE
OF THUNDERSTORMS WILL CONTINUE OVER THE EASTERN MOUNTAINS THROUGH
THE WEEKEND. COASTAL CLOUDS AND FOG CAN BE EXPECTED MOST NIGHTS AND
MORNINGS WITH ABOVE NORMAL TEMPERATURES CONTINUING ACROSS THE
INTERIOR.

SHORT TERM (TONIGHT THROUGH SATURDAY)...THE SHORTWAVE ENERGY THAT
PRODUCED SOME HIGH-BASED CONVECTION THIS MORNING OVER PARTS OF
MENDOCINO COUNTY HAS PUSHED TO THE NORTH AND EAST SPARKING OFF NEW
THUNDERSTORMS FROM THE TRINITY ALPS NORTH INTO SISKIYOU COUNTY.
SUBSIDENCE JUST BEHIND THE WAVE OF ENERGY HAS SUPPRESSED THE
ACTIVITY SOMEWHAT...BUT CUMULUS WAS RE-BUILDING ACROSS EASTERN
PORTIONS OF THE AREA AS OF 21Z WITH THE HEATING OF THE DAY.
THUNDERSTORMS ARE EXPECTED TO REDEVELOP OVER THE HIGHER TERRAIN
WITH ISOLATED TO SCATTERED THUNDERSTORMS POSSIBLE LATER THIS
AFTERNOON AND EVENING. THE BEST CHANCE BEING OVER THE TRINITY
ALPS. INSTABILITY REMAINS GOOD WITH MID-LEVEL LAPSE RATES OF 7 TO
9 C/KM...LI VALUES DOWN TO -7C...AND SBCAPE VALUES UP TO 2000
J/KG. A STABLE MID-LAYER IS PRESENT...AND BUILD-UPS ARE HAVING A
DIFFICULT TIME BREAKING THROUGH THE CAP...BUT WITH DIFFERENTIAL
HEATING AND ADDITIONAL FORCING FROM MORE SHORTWAVE ENERGY EXPECTED
TO MOVE NORTH INTO THE AREA LATER THIS AFTERNOON...THINK THAT THE
THUNDERSTORM COVERAGE WILL BE SIMILAR TO YESTERDAY.

A DISTINCT CLEARING LINE WAS EVIDENT ON THE VISIBLE SATELLITE
IMAGERY AS OF 21Z WITH STRATUS PEELING SOUTH OFF OF CAPE BLANCO
UNDER NORTHERLY FLOW. EXPECT CLOUDS TO REDEVELOP ALONG THE REDWOOD
AND MENDOCINO COASTS OVERNIGHT...ALTHOUGH MODELS SHOW DRIER BL RH
NORTH OF CRESCENT CITY. FOR NOW...HAVE KEPT AREAS NORTH OF PT ST
GEORGE PARTLY CLOUDY. GOING INTO THURSDAY...MORE CLEARING ALONG THE
COAST IS POSSIBLE WITH A DEEPER MARINE LAYER AND BETTER MIXING.

HAVE CONTINUED A SLIGHT CHANCE OF THUNDERSTORMS OVER THE EASTERN
MOUNTAINS EACH AFTERNOON AND EVENING INTO THE WEEKEND AS MODELS
KEEP NORTHWEST CALIFORNIA BETWEEN BROAD UPPER LEVEL TROUGHING OVER
THE NE PACIFIC AND HIGH PRESSURE OVER THE DESERT SOUTHWEST
ROTATING MONSOONAL MOISTURE NORTHWARD. AS WITH PREVIOUS DAYS...A STABLE
MID- LAYER IS PRESENT...BUT THUNDERSTORMS HAVE FOUND A WAY TO
BREAK THROUGH IT IN PREVIOUS DAYS. THIS WILL NEED TO BE MONITORED.

COASTAL CLOUDS/FOG CAN BE EXPECTED MOST NIGHTS/MORNINGS. HIGH
TEMPERATURES ACROSS INTERIOR VALLEY LOCATIONS WILL RANGE FROM THE
90S TO NEAR 100 F...WITH 60S AND 70S F ALONG THE COAST. STP

LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY) AFTERNOON
THUNDERSTORM POTENTIAL WILL PERSIST THROUGH THE END OF THE WEEKEND
INTO EARLY NEXT WEEK AS THE UPPER LEVEL LOW OFF THE COAST OF BRITISH
COLUMBIA PINWHEELS VORTICITY MAXIMUMS ACROSS THE PACIFIC NORTHWEST.
BOTH THE GFS AND ECMWF ARE SIGNALING FOR A CUT-OFF LOW TO DEVELOP
JUST OFF THE CENTRAL CALIFORNIA COAST LATE SUNDAY INTO MONDAY.
MODELS SHOW IT SHIFTING TO THE NE EARLY NEXT WEEK WITH THE NORTHERN
PERIPHERY OF THE LOW IMPACTING THE EUREKA COUNTY WARNING AREA
TUESDAY AND WEDNESDAY. THIS SHOULD PROLONG AFTERNOON THUNDERSTORM
POTENTIAL ACROSS EASTERN TRINITY THROUGH WEDNESDAY AFTERNOON. SLIGHT
CHANCES FOR THUNDERSTORMS WERE MAINTAINED THROUGH THE EXTENDED
FORECAST, HOWEVER, I ONLY INCREASED POPS ON WEDNESDAY AFTERNOON
SINCE THERE IS STILL SOME UNCERTAINTY IN THE MODELS WITH THE
TRACKING OF THE CUT-OFF LOW. OTHERWISE WARM TEMPERATURES ACROSS
INTERIOR AREAS WILL PERSIST INTO NEXT WEEK AS MODEL GUIDANCE TOOLS
SHOW A HIGH PREDICTABILITY IN THE UPPER LEVEL RIDGE REMAINING
STATIONED OVER THE WESTERN UNITED STATES. /KML

AVIATION...NORTHERLY FLOW AND CLEARING SKIES HAS BEEN SPREADING
SOUTHWARD ALONG THE OREGON COAST THROUGH THE DAY. THE CLEAR/DRY
SLOT IN VISIBLE IMAGERY HAS BEEN ENTERING THE NORCAL COASTAL WATERS.
HOWEVER SEVERAL SMALL SCALE VORTICES WERE PRESENT NEARSHORE FROM PT
ST GEORGE TO PT ARENA. THIS DOES NOT BODE WELL FOR CLEARING SKIES
ALONG THE COAST THIS EVENING. THUS EXPECT IFR CONDITIONS TO PREVAIL
THROUGH THIS EVENING ALONG THE COAST. CONDITIONS SHOULD DETERIORATE
TO LIFR AGAIN AND PUSH INTO THE NORTH COAST RIVER VALLEYS THIS
EVENING AS WELL. A SHORTWAVE TROUGH MOVING THROUGH THE AREA TODAY WILL
CONTINUE TO PRODUCE SCATTERED CBS AND ISOLATED TSTMS THROUGH EARLY
EVENING OVER THE TRINITY COUNTY MTNS. ANOTHER VORT MAX WILL APPROACH
ON THU AND EXPECT MORE INTERIOR CONVECTION.

MARINE...THE PACIFIC RIDGE OF HIGH PRESSURE AND THE THERMAL TROUGH
OVER CALIFORNIA WILL CONTINUE TO MAINTAIN MODERATE TO FRESH WINDS
AND STEEP SEAS THROUGH THE WEEKEND. HIGHEST WINDS AND SEAS WILL BE
FARTHER OFFSHORE. HOWEVER, AREAS NEARSHORE AROUND CAPE MENDOCINO
AND POINT ARENA MAY OBSERVE HIGHER WINDS AND STEEPENING SEAS.
OCCASIONAL GALE FORCE WINDS ARE POSSIBLE ACROSS THE OUTER WATERS
THIS WEEKEND BUT DO NOT ANTICIPATE NEEDING A GALE WARNING AT THIS
TIME SINCE CONDITIONS ARE FORECAST TO BE MARGINAL. AS FOR THE
INNER WATERS, CONDITIONS WILL BE LOWER BUT STILL REMAIN STEEP WITH
SOME AREAS REACHING SMALL CRAFT CRITERIA (ESPECIALLY NEAR CAPE
MENDOCINO AND POINT ARENA). THE INNER WATERS WILL NEED TO BE
MONITORED FOR ADVISORIES IF HIGH CONDITIONS SHOULD BECOME MORE
WIDESPREAD. MODELS SHOW LITTLE CHANGES IN THE LARGER SCALE SURFACE
PATTERN WITH EMBEDDED SHORTWAVES THAT MAY ALLOW THE PRESSURE
GRADIENT TO EASE SLIGHTLY. SMALL CRAFT ADVISORIES FOR THE OUTER
WATERS WILL LIKELY NEED TO BE EXTENDED INTO EARLY NEXT WEEK,
HOWEVER, HELD OFF ON MAKING ANY CHANGES TO THE END TIME DUE TO
UNCERTAINTY IN THE STRENGTH AND TIMING OF THE SHORTWAVES AND HOW
THEY WILL EFFECT THE PRESSURE GRADIENT OFFSHORE. /KML

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 5 PM PDT SUNDAY PZZ470-475.

&&

$$

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