Area Forecast Discussion
Issued by NWS Eureka, CA

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000
FXUS66 KEKA 201030
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
330 AM PDT SAT SEP 20 2014

.SYNOPSIS...HIGH PRESSURE WILL BRING DRY CONDITIONS AND WARM
TEMPERATURES TO MUCH OF NORTHWEST CALIFORNIA THROUGH THE WEEKEND.
COASTAL CLOUDS WILL RETURN THIS WEEKEND AS A SOUTHERLY SURGE OF
STRATUS MOVES UP THE NORTHWEST CALIFORNIA COAST.


&&

.DISCUSSION...AN UPPER LEVEL LOW CONTINUES TO SPIN OVER CENTRAL
CALIFORNIA WITH HIGH PRESSURE NOSING INTO THE PACIFIC NORTHWEST.
THIS HAS ALLOWED OFFSHORE FLOW TO DEVELOP OVER NORTHWEST CALIFORNIA
RESULTING IN MOSTLY CLEAR SKIES AND WARM TEMPERATURES. HOWEVER...AS
THE THERMAL TROUGH HAS MOVED WEST OFF THE COAST...A STRATUS SURGE
HAS DEVELOPED AND HAS PUSHED AS FAR NORTH AS TRINIDAD AS OF 3 AM.
WITH THE UPPER LOW OVER CENTRAL CALIFORNIA ANTICIPATED TO SLIDE
NORTHEAST ON SUNDAY AHEAD OF AN ADVANCING UPPER TROUGH OVER THE
PACIFIC...SOUTHERLY FLOW ALONG THE COAST SHOULD ONLY INCREASE
ALLOWING THE STRATUS TO CONTINUE TO SPREAD NORTH. AREAS OF COASTAL
FOG WILL BE THE RULE FOR THE NEXT FEW DAYS WITH A STRONG MARINE
INVERSION SPREADING NORTH TODAY INTO EARLY NEXT WEEK.

MODELS CONTINUE TO BE IN GREAT AGREEMENT THROUGH THURSDAY AS THE
NEXT SIGNIFICANT TROUGH APPROACHES AND IMPACTS THE COAST. A DEEP
TROUGH CURRENTLY OVER THE CENTRAL PACIFIC WILL WEAKEN AS IT
APPROACHES ON MONDAY LEADING TO ONLY SOME INCREASING HIGH CLOUDS AND
A POSSIBLE DEEPENING MARINE LAYER. THE NEXT BIG WEATHER MAKER WILL
BE THE NEXT TROUGH WHICH WILL BE POWERFUL ENOUGH TO PUSH A STRONG
COLD FRONT ONTO THE WEST COAST BY WEDNESDAY. THERE IS STILL SOME
UNCERTAINTY AS TO EXACTLY WHEN THE FRONT WILL ARRIVE WITH
POSSIBILITIES RANGING FROM EARLY WEDNESDAY MORNING TO WEDNESDAY
AFTERNOON...BUT IN GENERAL THERE IS HIGH CONFIDENCE IN THE
EXPECTATION OF WIDESPREAD RAIN FOR THE REGION SOMETIME ON WEDNESDAY.

CONSIDERING THE FRONT WILL BE STRONGLY FORCED AND PRECIPITABLE WATER
WILL POSSIBLY EXCEED 1.5 INCHES...THERE IS A DECENT CHANCE FOR THE
BAND OF PRECIPITATION TO BE HEAVY AT TIMES AS IT MOVES THROUGH THE
AREA. MODEL GUIDANCE CONTINUES TO INDICATE AT LEAST SOME CAPE OVER
THE INTERIOR WITH THE FRONTAL PASSAGE SO IT WOULD NOT BE A SURPRISE
TO SEE A LIGHTNING STRIKE OR TWO EVEN WITH NOT PARTICULARLY STRONG
LAPSE RATES EXPECTED. A BRIEF LULL IN SHOWER ACTIVITY IS ANTICIPATED
WEDNESDAY NIGHT OR EARLY THURSDAY MORNING BEFORE ADDITIONAL UPPER
LEVEL ENERGY AND THE POST FRONTAL TROUGH MOVES ONSHORE LEADING TO
ENHANCED SHOWER ACTIVITY ONCE AGAIN ON THURSDAY. AGAIN...THERE WILL
BE SOME INSTABILITY AROUND WITH COOL TEMPERATURES ALOFT LEADING TO
THE CHANCE OF AN ISOLATED THUNDERSTORM. AT THIS TIME NO
THUNDERSTORMS HAVE BEEN INTRODUCED INTO THE FORECAST CONSIDERING THE
LOW PROBABILITIES BUT THIS WILL NEED TO BE MONITORED OVER THE NEXT
SEVERAL DAYS. 850 MB TEMPERATURES ARE EXPECTED TO FALL TO AROUND 5C
WITHIN THE CORE OF THE TROUGH WHICH WILL RESULT IN MUCH COOLER
SURFACE TEMPERATURES OVER THE REGION...BUT NOT COOL ENOUGH TO EXPECT
ANY SMALL HAIL WITH THE SHOWERS ON THURSDAY. A DRYING TREND WILL
LIKELY BEGIN ON FRIDAY AS THE TROUGH MOVES INLAND THOUGH MODELS
REMAIN INCONSISTENT IN THE FAR EXTENDED. RPA


&&

.AVIATION...SOUTHERLY FLOW HAS BEEN DRAWING STRATUS NORTHWARD
AROUND CAPE MENDOCINO EARLY THIS MORNING. OFFSHORE WIND FLOW
OVER THE MOUNTAINS HAS THUS FAR KEPT THE STRATUS OUT OF KACV AND
KCEC...THOUGH PATCHY LOW CLOUDS HAVE FORMED AROUND HUMBOLDT BAY
AND THE PENINSULA. THE EASTERLY FLOW SHOULD KEEP THE BULK OF THE
STRATUS OFFSHORE THIS MORNING. ONSHORE FLOW THIS AFTERNOON AND
EVENING WILL LIKELY DRAW THE LOW CLOUDS ONTO THE COAST. THE LAYER
IS SHALLOW AND SMASHED...SO VSBY REDUCTION DUE TO FOG IS LIKELY.

&&

.MARINE...EXPANDED THE SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS TO
INCLUDE PZZ450 UNTIL MID MORNING WITH BUOYS REPORTING NORTHERLY
SEAS AROUND 7 FT AT 7 SECONDS. NORTHERLY WINDS IN THE NORTHERN
OUTER WATERS WILL EASE UP EARLY THIS MORNING AS LOW PRESSURE
DEVELOPS NORTH OF THE REGION OVER OREGON. WINDS HAVE ALREADY GONE
SOUTHERLY SOUTH OF CAPE MENDO AND WILL GO SOUTHERLY ACROSS THE
REMAINDER OF THE WATERS LATER THIS MORNING. INCREASED THE WIND
MAGNITUDE TODAY AND THIS EVENING ABOVE THE MODEL GUIDANCE
ESPECIALLY AROUND THE CAPE. EVEN THE HIGH RESOLUTION NAM12
TYPICALLY DOES NOT CAPTURE THE STRENGTH OF THE SOUTHERLIES VERY
WELL. WEAK SFC RIDGING SUN NIGHT INTO MON WILL LIKELY KEEP
GRADIENTS LOOSE AND WINDS ON THE LIGHT SIDE. AFTER SHORT PERIOD
SEAS LAY DOWN LATER THIS WEEKEND...THERE DOES NOT LOOK TO BE ANY
WAVES OF PARTICULAR SIGNIFICANCE UNTIL A STORM SYSTEM GENERATES A
WESTERLY SWELL NEXT WEEK. THE GFS AND ECMWF HAVE BEEN FAIRLY
CONSISTENT ON THE WIND FIELDS. FOR NOW JUST RAN WITH THE OUTPUT
FROM THE WAVE MODELS WHICH HAVE THE SWELL PEAKING AROUND 12 FT ON
WED.



&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
NORTHWEST CALIFORNIA COASTAL WATERS...
     SMALL CRAFT ADVISORY UNTIL 10 AM PDT THIS MORNING FOR PZZ450.

     SMALL CRAFT ADVISORY UNTIL 3 PM PDT THIS AFTERNOON FOR PZZ470.

&&

$$

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