028  
FXUS66 KEKA 032257  
AFDEKA  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE EUREKA CA  
357 PM PDT MON AUG 3 2015  
   
SYNOPSIS
 
A WEAK UPPER LEVEL SYSTEM WILL BRING ISOLATED  
AFTERNOON AND EVENING INLAND THUNDERSTORMS THROUGH TUESDAY. WEAK  
RIDGING WILL BRING DRY CONDITIONS WEDNESDAY AND THURSDAY WITH  
ANOTHER SYSTEM FRIDAY INTO THE WEEKEND BRINGING ADDITIONAL SHOWERS  
AND THUNDERSTORMS.  
 

 
   
SHORT TERM
 
(THROUGH THURSDAY) THE FIRST IN A SERIES OF WEAK UPPER  
LEVEL FEATURES HAS MOVED THROUGH THE REGION AND IS NOW TRIGGERING  
STORMS IN SISKIYOU COUNTY AND SOUTHERN OREGON. BETTER MIXING BEHIND  
THIS SYSTEM HAS RESULTED IN BETTER CLEARING OF THE SMOKE AND THUS  
MORE INSTABILITY OVER THE HIGHER PEAKS. AN ISOLATED SHOWER OR  
THUNDERSTORM WILL BE POSSIBLE THROUGH THE AFTERNOON AND EARLY  
EVENING HOURS...BUT IN GENERAL DRY CONDITIONS ARE EXPECTED THROUGH  
TUESDAY MORNING. ANOTHER SHORTWAVE TROUGH WILL MOVE OVERHEAD ON  
TUESDAY LEADING TO ANOTHER SLIGHT CHANCE OF THUNDERSTORMS OVER THE  
INTERIOR. MUCH LIKE TODAY THE TIMING OF THE SHORTWAVE PASSAGE WILL  
HAVE A MAJOR INFLUENCE ON THE POTENTIAL FOR STORMS AND CURRENTLY THE  
MODELS INDICATE THIS SHORTWAVE WILL MOVE THROUGH THE AREA IN THE MID  
AFTERNOON HOURS...PROVIDING THE TRIGGER THAT COULD INITIATE STORMS  
DURING PRIME HEATING. SO THUNDERSTORM CHANCES HAVE A BIT MORE AREAL  
COVERAGE TOMORROW OVER THE INTERIOR BUT STILL ONLY ISOLATED STORMS  
ARE ANTICIPATED.  
 
THESE SHORTWAVE TROUGHS WILL ALSO KEEP THE MARINE LAYER DEEP ALONG  
THE COAST...PUSHING STRATUS WELL INLAND TONIGHT AND TUESDAY NIGHT  
ACROSS MENDOCINO AND INTERIOR SOUTHERN HUMBOLDT COUNTY.  
 
A SHORTWAVE RIDGE WILL MOVE OVER NORTHWEST CALIFORNIA WEDNESDAY INTO  
THURSDAY LIKELY LEADING TO A SLIGHT COMPACTION OF THE MARINE LAYER  
AND SUBSIDENCE OVER THE INTERIOR RESTRICTING STORM FORMATION. THUS  
THE FORECAST IS DRY FOR WEDNESDAY AND THURSDAY.  
 
A MORE POTENT UPPER LEVEL LOW WILL APPROACH THE COAST THURSDAY  
NIGHT. DIFFLUENT FLOW ON THE EAST SIDE OF THE UPPER LOW WILL MOVE  
OVER THE CENTRAL CALIFORNIA COAST THURSDAY NIGHT...AND DEPENDING ON  
THE MID LEVEL LAPSE RATES...MAY ALLOW NOCTURNAL CONVECTION TO FORM  
OVER MENDOCINO COUNTY AND POSSIBLY SOUTHERN HUMBOLDT AND TRINITY  
COUNTIES. THIS POTENTIAL WILL BE WATCHED CLOSELY OVER THE NEXT FEW  
DAYS AND THUNDERSTORMS MAY NEED TO BE INTRODUCED TO THE  
OFFICIAL FORECAST. RPA  
   
LONG TERM...(FRIDAY THROUGH MONDAY)
 
FRIDAY AN UPPER LEVEL LOW  
JUST OFF OF THE CENTRAL CALIFORNIA COAST WILL MOVE INLAND, JUST TO  
OUR SOUTH. THIS LOW WILL BRING INSTABILITY TO OUR AREA WHILE ALSO  
TAPPING INTO SOME SUBTROPICAL MOISTURE. INCREASED THE AREAL COVERAGE  
FOR THUNDERSTORMS ON FRIDAY TO ACCOUNT FOR THIS, BUT KEPT THE SLIGHT  
CHANCE WORDING FOR NOW. AS THE LOW MOVES INLAND THE MODELS HINT AT  
NOCTURNAL THUNDERSTORMS FRIDAY NIGHT, FOLLOWED BY ANOTHER ROUND OF  
STORMS ON SATURDAY. BUT THIS LOOKS TO REMAIN MAINLY OVER EASTERN  
TRINITY COUNTY FOR NOW. LATE SATURDAY INTO SUNDAY AN UPPER LEVEL  
TROUGH STARTS TO SETTLE OVER THE PACIFIC NORTHWEST. THIS WILL LEAD  
TO INTERIOR TEMPERATURES SLIGHTLY BELOW NORMAL. BUT IT WILL ALSO  
CONTINUE THE SLIGHT CHANCE OF THUNDERSTORMS ACROSS MAINLY TRINITY  
COUNTY EACH AFTERNOON AND EARLY EVENING. THE THING TO NOTE IS  
NORTHWEST FLOW IS NOT A PARTICULARLY FAVORABLE PATTERN FOR  
THUNDERSTORMS, SO THIS WILL NEED TO BE WATCHED.  
 

 
   
AVIATION
 
AFTERNOON VISIBLE SATELLITE IMAGERY SHOWS STRATUS ALONG  
PORTIONS OF THE COAST WHILE THE INTERIOR HAS A MIX OF MOSTLY CLEAR  
SKIES, SOME CUMULUS CLOUDS, AND SMOKE/HAZE FROM MULTIPLE FIRES.  
ALONG THE COAST...STRATUS WILL OVERSPREAD THE ENTIRE COAST WHILE  
ALSO BEING PUSHED INLAND BY NORTHWEST WINDS. MVFR SHOULD TRANSITION  
TO IFR THIS EVENING AS CEILINGS LOWER. INLAND MENDOCINO COUNTY...VFR  
WILL PREVAIL THIS EVENING. STRATUS MAY MOVE OVER SOME OF THE  
VALLEYS, BRINGING MVFR. INLAND ELSEWHERE...SMOKE/HAZE AROUND  
MULTIPLE LARGE FIRES WILL BRING PARTIAL VISIBILITY REDUCTIONS.  
 

 
   
MARINE
 
BROAD LOW PRESSURE AND LOOSE GRADIENTS WILL REMAIN OVER  
THE AREA TONIGHT. HIGH PRESSURE OVER THE NE PACIFIC WILL START TO  
BUILD EASTWARD TOWARD THE PACIFIC NW COAST BY EARLY TUE  
MORNING...CREATING A TIGHTER PRESSURE GRADIENT OVER THE NORTHERN  
OUTER WATERS. THE GFS...ECMWF AND NAM12 INDICATE NORTHERLY WINDS  
REACHING 20KT IN THE NORTHERN 1/3RD OF PZZ470 BY TUE. THIS IS NOT  
QUITE ADVISORY LEVEL...HOWEVER NORTHERLY WINDS WILL CONTINUE TO  
INCREASE IN THE OUTER WATERS TUE NIGHT THROUGH WED. THE GFS  
CONTINUES TO INDICATE LOW END GALES ON THU...WITH GUSTS TO 35-40KT  
POSSIBLE OVER THE NORTHERN OUTER WATERS. IT IS STILL SEVERAL DAYS  
OUT AND THE MODELS CAN CHANGE. CONFIDENCE IS HIGH WINDS WILL  
INCREASE. THE EXACT MAGNITUDE IS STILL SKETCHY.  
 
SEAS HAVE BEEN AROUND 3 FT AT 7 SECONDS TODAY. THE NWPS AND ENP SHOW  
QUITE A MIX OF LONGER PERIOD WAVES ALL OF WHICH ARE FAIRLY  
SMALL...ABOUT 1 FT OR LESS. THE DOMINATING WAVE GROUP HAS BEEN  
CENTERED NEAR 8 SECONDS...SO WILL KEEP LEANING TOWARD THE SHORTER  
PERIOD WAVES IN THE FORECAST. THE NWPS AND ENP HAS WIND DRIVEN WAVES  
REACHING 5 TO 7 FT AT 7 SECONDS BY MID MORNING TUE IN PZZ470. THE  
SMALL CRAFT ADVISORY REMAINS UP FOR PZZ470 STARTING TUE MORNING.  
WIND-DRIVEN SEAS SHOULD CONTINUE TO INCREASE EACH DAY THROUGH THU.  
BASED ON OUR LOCAL CRITERIA...A WARNING FOR HAZARDOUS SEAS MAY BE  
NECESSARY IN THE OUTER WATERS IF SEAS REACH 10 FT OR MORE WITH  
PERIODS OF 8 SECONDS OR LESS. WE ARE FOLLOWING THE NWPS GUIDANCE  
WHICH HAS SEAS REACHING 13 FT ON THU IN PZZ470. THE ENP WAS A COUPLE  
OF FEET LESS...BUT STILL NEAR CRITERIA.  
 

 
   
FIRE WEATHER
 
A SERIES OF TWO UPPER LEVEL WAVES MAY TRIGGER  
ISOLATED STORMS OVER INTERIOR NORTHWEST CALIFORNIA THIS  
AFTERNOON/EVENING AND THEN AGAIN TUESDAY AFTERNOON/EVENING. ANY  
DEVELOPMENT WILL LIKELY BE LIMITED SO ONLY A HEADLINE WILL BE  
INCLUDED IN THE FIRE WEATHER FORECAST THROUGH TUESDAY. A BETTER  
CHANCE FOR STORMS WILL RETURN THURSDAY NIGHT THROUGH SATURDAY AS AN  
UPPER LEVEL LOW SLIDES THROUGH CENTRAL CALIFORNIA. THE BEST CHANCES  
FOR STORMS WILL BE OVER MENDOCINO...SOUTHERN HUMBOLDT...AND TRINITY  
COUNTIES WITH THE LOW MOVING INLAND WELL SOUTH OF THE AREA.  
CONFIDENCE IS STILL LOW IN THE NUMBER OF STORMS EXPECTED AT THIS TIME  
...BUT THERE IS THE POTENTIAL THAT STORMS COULD BECOME SCATTERED AND  
FIRE WEATHER WATCHES/WARNINGS COULD BE REQUIRED.  
 
THE MARINE LAYER PUSHED WELL INLAND LAST NIGHT AND SHOULD REACH  
SIMILAR LOCATIONS THE NEXT TWO NIGHTS AS THE UPPER LEVEL WAVES MOVE  
OVERHEAD. A RIDGE WEDNESDAY AND THURSDAY WILL LIKELY COMPACT THE  
MARINE LAYER SLIGHTLY RESTRICTING INLAND PENETRATION OF THE COASTAL  
CLOUDS. THUS OVERNIGHT RH RECOVERIES WILL BE GENERALLY GOOD THE NEXT  
TWO NIGHTS AND THEN BEGIN TO DECREASE WEDNESDAY NIGHT. RPA  
 

 
   
EKA WATCHES/WARNINGS/ADVISORIES
 
 
CA...NONE.  
NORTHWEST CALIFORNIA COASTAL WATERS...  
SMALL CRAFT ADVISORY FROM 8 AM TUESDAY TO 5 PM PDT FRIDAY FOR  
PZZ470.  
 

 
 

 
 
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