FXUS66 KEKA 201200
AFDEKA
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
400 AM PST TUE JAN 20 2009
.SYNOPSIS...AN UPPER LEVEL TROUGH APPROACHING THE CALIFORNIA
COAST WILL BRING CLOUDS AND A CHANCE OF SHOWERS WEDNESDAY
THROUGH SUNDAY.  
&&
.SHORT TERM...TODAY THROUGH THURSDAY...STRATUS WAS LURKING 40-60NM
OFFSHORE AND MOVING PARALLEL TO COAST EARLY THIS MORNING.
A FEW HIGH CLOUDS ASSOCIATED WITH AN APPROACHING UPPER LEVEL
TROUGH WERE ALSO SKIMMING OVER THE AREA. GFS AND NAM12 BOUNDARY
LAYER RH FIELDS REMAIN QUITE DRY TODAY...BUT WILL NOT RULE OUT
PATCHY OR SCATTERED LOW CLOUD DEVELOPMENT THIS AFTERNOON. IN 
ANY CASE...EXPECT IT WILL BE SUNNY FOR THE BETTER PART OF THE
DAY AFTER THE TYPICAL VALLEY FOG BURNS OFF ACROSS THE RIVER VALLEYS.
 
OVERNIGHT TEMPERATURES WERE RUNNING SEVERAL DEGREES LOWER MOST
EVERYWHERE...EVEN THOUGH EASTERLY WINDS WERE STILL GOING STRONG
OVER THE RIDGES. THE OFFSHORE FLOW WEAKENS TODAY AND EVEN GOES
WEAKLY ONSHORE THIS AFTERNOON. THE COOLING TREND OF DAYTIME 
HIGH TEMPS WILL CONTINUE ON WEDNESDAY AS THE OFFSHORE TROUGH
SPREADS THICKER CLOUD LAYERS OVER THE AREA. RAIN CHANCES LOOK
MARGINAL...BUT THE SOUTHWEST FLOW WILL BRING MOISTURE INTO
THE REGION AND HAVE ADDED AT LEAST A SLIGHT CHANCE OF SHOWERS
TO THE FORECAST. THE RAIN CHANCES LOOK BEST ACROSS THE INTERIOR AS 
THE TROUGH AXIS APPROACHES WED NIGHT. GFS HAS THE TROUGH SHEARING 
APART AND MOVING OVER NORTHWEST CALIFORNIA THURSDAY MORNING...WITH
A RIDGE BUILDING BEHIND. NAM12 WAS SLOWER AND KEEPS A SEMI-CLOSE
LOW/OPEN WAVE OVER NORTHERN CALIFORNIA THROUGH THURSDAY AFTERNOON
THEREFORE WILL MAINTAIN SHOWER CHANCES THROUGH THE AFTERNOON...WITH 
BEST CHANCES ACROSS THE EASTERN SECTIONS OF THE FORECAST AREA. DJB 
.LONG TERM...THURSDAY NIGHT THROUGH MONDAY...OPERATIONAL MODEL RUNS 
FROM THE EURO...NAM12 AND GFS WERE IN GOOD AGREEMENT ON KEEPING THE 
AREA IN SEMI-MOIST SOUTHWEST FLOW ALOFT THU NIGHT THROUGH FRI. MOIST 
AIR AND UPSLOPE FLOW SHOULD GENERATE ISOLATED OR SCATTERED SHOWERS 
PRIMARILY OVER THE INTERIOR THU NIGHT AND FRIDAY. 
SOLUTIONS CONTINUE TO STRUGGLE WITH A SECOND UPPER TROUGH EXPECTED 
TO AFFECT THE FORECAST REGION SAT->SUN. GFS ENSEMBLE MEAN INDICATES 
HIGHER PRECIP CHANCES FRI NIGHT AND AGAIN ON SUNDAY...AND HAVE EDGED 
PRECIP CHANCES TO NEAR CLIMO THESE PERIODS. WITH THE TIMING VARYING 
FROM ONE MODEL RUN TO THE NEXT AND THE VARIATIONS BETWEEN DIFFERENT 
GLOBAL MODELS...CONFIDENCE IN THE CHANCE OF RAIN IS BY NO MEANS 
HIGH. USED A WIDE-BROAD PAINT BRUSH APPROACH...WITH A SLIGHT CHANCE 
OF SHOWERS FOR EACH INTERVENING PERIOD AND ACROSS MUCH OF THE 
FORECAST AREA THROUGH MONDAY DUE TO THE UNCERTAINTY. DJB   
&&
.AVIATION...SATELLITE IMAGERY AND SURFACE OBSERVATIONS TONIGHT SHOW 
CLEAR SKIES ACROSS THE REGION...WITH NO CHANGE EXPECTED OVER THE 
NEXT 24 HOURS. WINDS WILL REMAIN LIGHT AND OFFSHORE KEEPING COASTAL 
LOCATIONS DRY AND FREE FROM FOG/STRATUS DEVELOPMENT. LOCALIZED 
INLAND VALLEY LOCATIONS MAY SEE SOME FOG INTO THE MORNING HOURS. 
NEXT CHANCE FOR RAIN AND WIDESPREAD LOW CIG/VSBY WILL START WED 
AFTERNOON AS AN UPPER LEVEL TROF PASSES OVER THE AREA. BK
&&
.MARINE...THE COASTAL WATERS CONTINUE TO EXPERIENCE AN EXTENDED 
PERIOD OF VERY LIGHT WINDS...WHICH WILL PERSIST THROUGH SATURDAY. AN 
INCREASE IN NORTHERLY WINDS...WITH POSSIBLE GUSTS TO 30 KT IS 
INDICATED BY THE MODELS STARTING SATURDAY NIGHT. WESTERLY SWELL 
CONTINUES TO MOVE THROUGH THE WATERS TONIGHT WITH HEIGHTS RUNNING 
AROUND 6 TO 7 FT AT 12 SECONDS...WITH A DECREASE IN WAVE HEIGHTS AND 
PERIOD EXPECTED THROUGH THURSDAY. A WESTERLY SWELL WILL BEGIN 
BUILDING THURSDAY NIGHT WITH MODEL GUIDANCE SUGGESTING A PEAK CLOSE 
TO 9 FEET FRIDAY NIGHT. PERIODS WILL BE ON THE ORDER OF 14 TO 16 
SECONDS. BK
&&
.EKA WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
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