876  
FXUS66 KEKA 212121  
AFDEKA  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE EUREKA CA  
221 PM PDT MON MAY 21 2018  
   
SYNOPSIS
 
MILD WEATHER CONDITIONS WILL PERSIST OVER THE NEXT  
SEVERAL DAYS WITH A SLIGHT CHANCE FOR AFTERNOON THUNDERSTORMS  
ACROSS INTERIOR MOUNTAINS AND STRATUS NEAR THE COAST. BUILDING  
HIGH PRESSURE WILL BRING WARMER AND DRIER WEATHER FOR MEMORIAL  
WEEKEND.  
 

 
   
DISCUSSION
 
WEAK RIDGING WILL MOVE OVER NORTHERN CALIFORNIA  
EARLY THIS WEEK AS A CLOSED LOW ACROSS THE SOUTHWEST LIFTS  
NORTHWARD. THIS HELPED TO CLEAR OUT CLOUD COVER ACROSS MOST OF THE  
REGION AND INCREASE INLAND TEMPERATURES BY 5 TO 10 DEGREES THIS  
AFTERNOON.  
 
500 MB HEIGHTS WILL BEGIN TO FALL ON TUESDAY AS ANOTHER  
UPPER TROUGH DIVES DOWN FROM THE GULF OF ALASKA AND BECOMES A CLOSED  
LOW PRESSURE SYSTEM OFF OF THE CALIFORNIA COAST BY WEDNESDAY  
AFTERNOON. THIS WILL DRAW IN LOW TO MID LEVEL MOISTURE ACROSS  
NORTHWEST CALIFORNIA WHICH WILL BRING A SLIGHT CHANCE FOR  
THUNDERSTORMS PRIMARILY ACROSS THE MOUNTAINOUS INTERIOR. BY THURSDAY  
AND FRIDAY, THE CLOSED LOW WILL TRACK OVER CENTRAL CALIFORNIA. THIS  
PATTERN TENDS TO BE MOST FAVORABLE FOR THUNDERSTORM DEVELOPMENT, AND  
WITH EAST/SOUTHEASTERLY FLOW, SHOWERS AND THUNDERSTORMS WILL BE ABLE  
TO TRACK TOWARDS COASTAL AREAS OF NORTHWEST CALIFORNIA. POPS WERE  
INCREASED FOR THURSDAY BUT WITHHELD FROM EXPANDING SLIGHT CHANCE FOR  
STORMS NEAR THE COAST AT THIS TIME. CHANCES FOR INLAND SHOWERS WILL  
DIMINISH INTO THE HOLIDAY WEEKEND AS HIGH PRESSURE SETS UP ALONG THE  
WEST COAST AND BRINGS WARMER AND DRIER AIR TO THE REGION.  
 
STRATUS WILL CONTINUE TO IMPACT MUCH OF THE COAST AND INTERIOR  
VALLEYS THROUGH MUCH OF THE WEEK WITH WEAKER WINDS FORECAST ACROSS  
THE COASTAL WATERS AND HIGH HUMIDITY ACROSS MOST OF THE REGION.  
INLAND AREAS WILL MORE READILY CLEAR OUT WITH AFTERNOON MIXING BUT  
CLOUDS WILL LINGER ALONG THE COAST. POCKETS OF THE COAST SHOULD  
STILL SEE SOME PEAKS OF BLUE SKIES IN THE AFTERNOONS.  
 
LOOKING SPECIFICALLY AT MEMORIAL WEEKEND, SHOWERS AND THUNDERSTORMS  
WILL BE THE MAIN IMPACT ON FRIDAY AND SATURDAY. HOWEVER, BUILDING  
HIGH PRESSURE WILL BRING DRIER CONDITIONS WITH INLAND TEMPERATURES  
INCREASING TO THE 70S AND 80S LATE IN THE WEEKEND. /KML  
 

 
   
AVIATION
 
THE MARINE LAYER REMAINED PERSISTENT BUT SORT OF  
FRAGMENTED ALONG THE COAST NORTH OF CAPE MENDOCINO THIS MORNING.  
HOWEVER, THE MARINE LAYER DID PUSH WELL INTO INTERIOR VALLEYS.  
MOST LOW CLOUDS AREAS BUSTED UP AROUND NOONDAY, NEVERTHELESS A  
LARGE SWATHE REMAINED OVER HUMBOLDT COUNTY: RANGES NORTH OF  
PETROLIA-WEOTT-BRIDGEVILLE-EEL DELTA-JUST WEST OF WILLOW CREEK AND  
THEN PRIMARILY NORTH NEAR TRINIDAD. PREVIOUS DISCUSSION PORTIONS:  
THE DAYTIME MIXING AND DRYING FOR SITES AT THE COAST WILL BE  
FIGHTING AGAINST A MOIST ONSHORE FLOW WHICH WILL LIKELY LEAD TO  
MORE CLOUD GENERATION THIS AFTERNOON. THUS, EXPECT MVFR CEILINGS  
TO QUICKLY SPREAD BACK OVER THE COASTAL PLAIN AND TERMINALS BY  
THIS EVENING. THERE IS A POTENTIAL FOR CEILINGS DROPPING BELOW  
1000 FEET AS WE HEAD INTO THE EARLY MORNING HOURS OF  
TUESDAY...(ADDED) AND MODEL GUIDANCE CERTAINLY SUPPORTS THIS  
SCENARIO. /TA  
 

 
   
MARINE
 
AN ASCAT PASS THIS AFTERNOON OBSERVED STRONG TO NEAR GALE  
FORCE WINDS PRIMARILY ACROSS THE OUTER WATERS TODAY WITH BUOYS  
REPORTING STEEP SEAS AROUND 6 TO 9 FEET. NORTHERLIES WILL DECREASE  
THROUGH TONIGHT AS THE PRESSURE GRADIENT RELAXES THEN LIGHT TO  
MODERATE WINDS WILL PERSIST THROUGH MOST OF THE WEEK. SHORT PERIOD  
SEAS WILL STEADILY SUBSIDE THROUGH TUESDAY WITH A MIXED SEA STATE  
AROUND 6 TO 8 FEET EXPECTED THROUGH THE WORK WEEK. SEAS SHOULD BE  
RELATIVELY LOW THROUGH MEMORIAL WEEKEND BUT MODERATE NORTH WINDS  
WILL DEVELOP LATE IN THE WEEKEND WITH 20 KT GUSTS POSSIBLE PRIMARILY  
SOUTH OF CAPE MENDOCINO. PLEASE STAY TUNED FOR POSSIBLE CHANGES  
IN THE EXTENDED FORECAST. /KML  
 

 
   
EKA WATCHES/WARNINGS/ADVISORIES
 
 
CA...NONE.  
NORTHWEST CALIFORNIA COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 5 PM PDT TUESDAY FOR PZZ450-455-470-  
475.  
 

 
 

 
 
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