901  
FXUS66 KEKA 231207  
AFDEKA  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE EUREKA CA  
507 AM PDT SUN JUL 23 2017  
   
SYNOPSIS
 
 
ISOLATED THUNDERSTORMS MAY DEVELOP THROUGH LATE TUESDAY FOR PORTIONS  
OF NORTHWESTERN CALIFORNIA THROUGH LATE TUESDAY. OTHERWISE, LOOK FOR  
CLOUDS AND PATCHY FOG TO DEVELOP DURING THE NIGHT AND INTO THE  
MORNING ALONG THE COAST AND INTO A FEW OF THE COASTAL RIVER VALLEYS.  
FARTHER INLAND, HOT AND DRY CONDITIONS WILL PREVAIL FOR THE  
INTERIOR.  
 

 
   
DISCUSSION
 
   
SHORT TERM
 
 
(TODAY AND TONIGHT)  
 
THE FORECAST STARTS TO GET A LITTLE MORE INTERESTING FOR TODAY, AS  
IT'LL BE THE FIRST OF A FEW DAYS OF POTENTIAL CONVECTIVE  
DEVELOPMENT. ASIDE FROM SEEING THE TYPICAL COASTAL STRATUS DEVELOPING  
THIS MORNING, THE MAIN INTEREST OF NOTE SEEN ON THE NEW NON-  
OPERATIONAL GOES-16 LOW-LEVEL WATER VAPOR INFRA-RED IMAGERY IS THE  
DEVELOPMENT OF ALTOCUMULUS CLOUDS, AS THEY SPREAD NORTHWARD.  
COVERAGE OF THESE CLOUDS HAS BEEN ON THE INCREASE OVER THE LAST FEW  
HOURS. THIS IS INDICATIVE OF A MOISTENING/DESTABILIZING EFFECT IN  
THE MID LEVELS OF THE ATMOSPHERE AND TYPICALLY A PRECURSOR FOR  
POTENTIAL CONVECTIVE DEVELOPMENT.  
 
THIS DEVELOPMENT IS WHERE THE REAL CHALLENGE LIES TODAY, AS THE  
WETTER GFS MODEL HAS TRENDIER DRIER TOWARDS THE MAJORITY OF THE  
VARIOUS CONVECTIVE MODELS. HOWEVER, TAKING A CLOSER LOOK AT  
SOUNDINGS ACROSS EASTERN DEL NORTE, NORTHEASTERN HUMBOLDT, AND  
NORTHERN/SOUTHEASTERN TRINITY COUNTIES, A GOOD AMOUNT OF INSTABILITY  
IS SEEN IN MOST AT MOST OF THESE FORECAST POINTS. BOTH THE NAM AND  
GFS GENERATE AROUND 2000 J/KG OF SBCAPE, WITH LIFTED INDICES DOWN TO  
-4 AND MID-LEVEL LAPSE RATES NEAR 8 DEG. C/KM. ADDITIONALLY,  
PRECIPITABLE WATER VALUES ARE FORECAST TO INCREASE, WITH  
DISTURBANCES ROTATING AROUND A DEVELOPING OFFSHORE LOW PROVIDING THE  
FOCUS/ASCENT FOR A STORM OR TWO TO POSSIBLY DEVELOP. SHOULD THIS  
OCCUR, CLOUD TO GROUND LIGHTNING AND GUSTY WINDS WILL BE THE MAIN  
STORM CONCERNS. THIS IS ESPECIALLY TRUE FOR TRINITY COUNTY, WHERE  
MUCH WARMER TEMPERATURES WILL LEAD TO SURFACE DEWPOINT DEPRESSIONS  
IN EXCESS OF 50 DEGREES FAHRENHEIT WILL BE LIKELY. HERE, CLOUD  
BASES COULD BE NEAR 13,000 FEET, COMPARED TO 8000 FEET FURTHER  
NORTHWEST. ANY STORM WHICH DEVELOPS WILL BE FAIRLY SLOW-MOVING, AS  
MEAN WIND SPEEDS ARE IN THE 10 TO PERHAPS 15 KNOT RANGE.  
 
OUR CONVECTIVE POTENTIAL WILL START TO WANE WITH THE LOSS OF HEATING  
AT SUNSET, WITH ATTENTION THEN TURNING TO COASTAL STRATUS AND PATCHY  
FOG DEVELOPMENT OVERNIGHT.  
   
LONG TERM
 
 
(MONDAY THROUGH SATURDAY)  
 
THUNDERSTORM POTENTIAL CONTINUES TO BE THE MAIN CHALLENGE FOR THE  
FIRST PART OF THE FORECAST. OVERALL, THE MODELS SHOW A SOMEWHAT  
BETTER CONVECTIVE SIGNAL FOR MONDAY, AND MORESO ON TUESDAY. DURING  
THIS TIME, THE OFFSHORE MID-LEVEL LOW WILL CONTINUE TO DEEPEN SOME  
MONDAY BEFORE SLOWLY LIFTING NORTHEAST ACROSS THE AREA ON TUESDAY.  
DISTURBANCES ROTATING AROUND THE LOW WILL CONTINUE TO BRING BURSTS  
OF LIFT WHICH COULD INTERACT WITH ANY POTENTIAL INSTABILITY,  
ENHANCING OUR THUNDERSTORM THREAT. SOUNDINGS CONTINUE TO SHOW GOOD  
INSTABILITY DURING THE AFTERNOON AND EVENING EACH DAY. IN FACT,  
INSTABILITY LOOKS PERSIST INTO AT LEAST THE EARLY MORNING HOURS  
TUESDAY, WITH AN EVEN GREATER DURATION SEEN OVERNIGHT INTO WEDNESDAY  
MORNING. DANGEROUS CLOUD TO GROUND LIGHTNING AND GUSTY WINDS WILL  
CONTINUE TO BE THE MAIN STORM CONCERNS. HOWEVER, LIFT WILL INCREASE  
AS THE LOW APPROACHES, INCREASING LAPSE RATES ALOFT WITH A FAT CAPE  
DENSITY SEEN IN THE -10 TO -30 DEG. C LAYER. THIS MAKES SMALL HAIL  
MORE OF A CONCERN WITH ANY STRONG STORM THAT DEVELOPS.  
 
FOR THE REMAINDER OF THE WEEK, AS THE LOW LIFTS AWAY FROM THE  
REGION, DRIER AIR WILL RETURN TO THE REGION WITH TEMPERATURES  
GENERALLY NEAR SEASONAL VALUES. /PD  
 

 
   
AVIATION
 
 
AN EXPANSIVE AREA OF MARINE STRATUS IS YIELDING IFR  
CEILINGS/VISIBILITY ACROSS THE HUMBOLDT AND DEL NORTE COAST THIS  
MORNING. SIMILAR TO PAST DAYS, SKIES WILL LIKELY EXPERIENCE  
CLEARING DURING THE AFTERNOON, FOLLOWED BY THE REDEVELOPMENT OF  
STRATUS AND LOWERED CEILINGS DURING THE OVERNIGHT HOURS. IN  
ADDITION, THERE IS SOME POTENTIAL THAT THE REMNANTS OF AFTERNOON  
MOUNTAIN THUNDERSTORM ACTIVITY COULD SPREAD WEST TOWARD CEC DURING  
THE EVENING. FARTHER SOUTH AT UKI, MODEL GUIDANCE HINTS AT THE  
POSSIBILITY FOR SHALLOW STRATUS DEVELOPING LATE TONIGHT...WILL  
CONTINUE TO MONITOR.  
 

 
   
MARINE
 
 
SUSTAINED GALE FORCE NORTHERLIES ARE EXPECTED TO DEVELOP/PERSIST  
OVER THE NRN OUTER WATERS TODAY THROUGH MONDAY EVENING. ELSEWHERE  
(WITH THE EXCEPTION OF MARINE ZONE 455), HAZARDOUS SEAS, WITH  
WAVES RANGING FROM 10 TO 13 FEET AT 8 TO 11 SECONDS, WILL SPREAD  
SOUTH ACROSS THE NRN INNER WATERS, AND SRN OUTER WATERS TODAY INTO  
PART OF MONDAY. MODEL GUIDANCE CONTINUES TO SHOW A THERMAL TROUGH  
EXPANDING WESTWARD ACROSS THE COAST BY EARLY TO MID NEXT WEEK,  
WHICH WILL AID IN SHUNTING STRONG WINDS AND STEEP WIND WAVES  
FARTHER OFFSHORE...THE END RESULT BEING IMPROVING MARINE  
CONDITIONS.  
 

 
   
FIRE WEATHER
 
 
ISOLATED THUNDERSTORMS WILL BE THE MAIN FIRE WEATHER CONCERN OVER  
THE NEXT FEW DAYS, WITH THE CONVECTIVE POTENTIAL INCREASING EACH  
DAY. AT THIS TIME, THE BEST POTENTIAL TO SEE DRY THUNDERSTORMS LOOKS  
TO BE OVER TRINITY COUNTY (SEE DISCUSSION ABOVE), WITH WET OR HYBRID  
TYPE STORMS POSSIBLE FARTHER NORTHWEST. FOR MONDAY THROUGH WEDNESDAY  
MORNING, THUNDERSTORMS LOOK TO BE INCREASINGLY WET, AS MOISTURE  
INCREASES ACROSS THE REGION AND STORM MOVEMENT SPEEDS DECREASE. /PD  
 

 
   
EKA WATCHES/WARNINGS/ADVISORIES
 
 
CA...NONE.  
NORTHWEST CALIFORNIA COASTAL WATERS...HAZARDOUS SEAS WARNING UNTIL 5 AM PDT MONDAY FOR PZZ450.  
 
GALE WARNING UNTIL 11 PM PDT MONDAY FOR PZZ470.  
 
SMALL CRAFT ADVISORY UNTIL 11 AM PDT THIS MORNING FOR PZZ455.  
 
HAZARDOUS SEAS WARNING UNTIL 11 PM PDT MONDAY FOR PZZ475.  
 

 
 

 
 
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