998  
FXUS66 KEKA 310321  
AFDEKA  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE EUREKA CA  
821 PM PDT WED JUL 30 2014  
   
SYNOPSIS
 
SHOWERS AND THUNDERSTORMS ARE TAPERING QUICKLY THIS  
EVENING OVER TRINITY COUNTY. HOWEVER...AN UPPER SHORTWAVE TROUGH  
APPROACHING FROM THE SW WILL CROSS NW CALIFORNIA OVERNIGHT  
BRINGING A SLIGHT CHANCE OF DRY LIGHTNING OVER MENDOCINO COUNTY.  
OTHERWISE...FAIR CONDITIONS WILL PREVAIL ACROSS THE INTERIOR WHILE  
LOW CLOUDS AND FOG SETTLE IN ALONG THE COAST. MORE THUNDERSTORMS  
ARE EXPECTED ACROSS EASTERN TRINITY COUNTY THURSDAY AFTERNOON.  
 

 
   
UPDATE
 
THROUGH COORDINATION WITH THE USFS REDDING FIRE WEATHER  
OFFICE, HAVE ADDED IN A SLIGHT CHANCE OF DRY LIGHTNING OVERNIGHT  
TO MENDOCINO, FAR SOUTHERN TRINITY, AND EXTREME SE HUMBOLDT  
COUNTIES. ANOTHER SHORTWAVE TROUGH, SIMILAR TO LAST NIGHT, IS  
APPROACHING FROM THE SW THIS EVENING. WHILE NOT AS VIGOROUS AS THE  
PREVIOUS NIGHT, THIS SHORTWAVE IS SHOWING ACCAS IN EVENING  
SATELLITE IMAGERY GIVING ME JUST ENOUGH CONFIDENCE TO ADD DRY  
THUNDERSTORMS TO THE FORECAST. THAT SAID, CONFIDENCE IS RATHER LOW  
OF SOMETHING OCCURRING, BUT WOULD BE REMISS TO NOT HAVE DRY  
LIGHTNING IN THE FORECAST. HAVE NOT ISSUED ANY FIRE WEATHER  
WATCHES OR WARNING DUE TO THE LOW CONFIDENCE. THIS THREAT WILL END  
AS THE WAVE PASSES OVERNIGHT.  
OTHERWISE, THE FORECAST REMAINS ON TRACK. BFG  
 
IF YOU WITNESS ANY LIGHTNING OVERNIGHT PLEASE LET US KNOW THROUGH  
OUR SOCIAL MEDIA CONTACTS AT THE BOTTOM OF THIS DISCUSSION. IF YOU  
SEE A WILDFIRE, PLEASE REPORT IT TO YOUR LOCAL FIRE AGENCY.  
 

 
   
PREV DISCUSSION......ISSUED AT 340 PM PDT
 
 
SYNOPSIS...ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED OVER  
THE TRINITY ALPS THIS AFTERNOON AND EARLY EVENING. A SLIGHT CHANCE  
OF THUNDERSTORMS WILL CONTINUE OVER THE EASTERN MOUNTAINS THROUGH  
THE WEEKEND. COASTAL CLOUDS AND FOG CAN BE EXPECTED MOST NIGHTS AND  
MORNINGS WITH ABOVE NORMAL TEMPERATURES CONTINUING ACROSS THE  
INTERIOR.  
 
SHORT TERM (TONIGHT THROUGH SATURDAY)...THE SHORTWAVE ENERGY THAT  
PRODUCED SOME HIGH-BASED CONVECTION THIS MORNING OVER PARTS OF  
MENDOCINO COUNTY HAS PUSHED TO THE NORTH AND EAST SPARKING OFF NEW  
THUNDERSTORMS FROM THE TRINITY ALPS NORTH INTO SISKIYOU COUNTY.  
SUBSIDENCE JUST BEHIND THE WAVE OF ENERGY HAS SUPPRESSED THE  
ACTIVITY SOMEWHAT...BUT CUMULUS WAS RE-BUILDING ACROSS EASTERN  
PORTIONS OF THE AREA AS OF 21Z WITH THE HEATING OF THE DAY.  
THUNDERSTORMS ARE EXPECTED TO REDEVELOP OVER THE HIGHER TERRAIN  
WITH ISOLATED TO SCATTERED THUNDERSTORMS POSSIBLE LATER THIS  
AFTERNOON AND EVENING. THE BEST CHANCE BEING OVER THE TRINITY  
ALPS. INSTABILITY REMAINS GOOD WITH MID-LEVEL LAPSE RATES OF 7 TO  
9 C/KM...LI VALUES DOWN TO -7C...AND SBCAPE VALUES UP TO 2000  
J/KG. A STABLE MID-LAYER IS PRESENT...AND BUILD-UPS ARE HAVING A  
DIFFICULT TIME BREAKING THROUGH THE CAP...BUT WITH DIFFERENTIAL  
HEATING AND ADDITIONAL FORCING FROM MORE SHORTWAVE ENERGY EXPECTED  
TO MOVE NORTH INTO THE AREA LATER THIS AFTERNOON...THINK THAT THE  
THUNDERSTORM COVERAGE WILL BE SIMILAR TO YESTERDAY.  
 
A DISTINCT CLEARING LINE WAS EVIDENT ON THE VISIBLE SATELLITE  
IMAGERY AS OF 21Z WITH STRATUS PEELING SOUTH OFF OF CAPE BLANCO  
UNDER NORTHERLY FLOW. EXPECT CLOUDS TO REDEVELOP ALONG THE REDWOOD  
AND MENDOCINO COASTS OVERNIGHT...ALTHOUGH MODELS SHOW DRIER BL RH  
NORTH OF CRESCENT CITY. FOR NOW...HAVE KEPT AREAS NORTH OF PT ST  
GEORGE PARTLY CLOUDY. GOING INTO THURSDAY...MORE CLEARING ALONG THE  
COAST IS POSSIBLE WITH A DEEPER MARINE LAYER AND BETTER MIXING.  
 
HAVE CONTINUED A SLIGHT CHANCE OF THUNDERSTORMS OVER THE EASTERN  
MOUNTAINS EACH AFTERNOON AND EVENING INTO THE WEEKEND AS MODELS  
KEEP NORTHWEST CALIFORNIA BETWEEN BROAD UPPER LEVEL TROUGHING OVER  
THE NE PACIFIC AND HIGH PRESSURE OVER THE DESERT SOUTHWEST  
ROTATING MONSOONAL MOISTURE NORTHWARD. AS WITH PREVIOUS DAYS...A STABLE  
MID- LAYER IS PRESENT...BUT THUNDERSTORMS HAVE FOUND A WAY TO  
BREAK THROUGH IT IN PREVIOUS DAYS. THIS WILL NEED TO BE MONITORED.  
 
COASTAL CLOUDS/FOG CAN BE EXPECTED MOST NIGHTS/MORNINGS. HIGH  
TEMPERATURES ACROSS INTERIOR VALLEY LOCATIONS WILL RANGE FROM THE  
90S TO NEAR 100 F...WITH 60S AND 70S F ALONG THE COAST. STP  
 
LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY) AFTERNOON  
THUNDERSTORM POTENTIAL WILL PERSIST THROUGH THE END OF THE WEEKEND  
INTO EARLY NEXT WEEK AS THE UPPER LEVEL LOW OFF THE COAST OF BRITISH  
COLUMBIA PINWHEELS VORTICITY MAXIMUMS ACROSS THE PACIFIC NORTHWEST.  
BOTH THE GFS AND ECMWF ARE SIGNALING FOR A CUT-OFF LOW TO DEVELOP  
JUST OFF THE CENTRAL CALIFORNIA COAST LATE SUNDAY INTO MONDAY.  
MODELS SHOW IT SHIFTING TO THE NE EARLY NEXT WEEK WITH THE NORTHERN  
PERIPHERY OF THE LOW IMPACTING THE EUREKA COUNTY WARNING AREA  
TUESDAY AND WEDNESDAY. THIS SHOULD PROLONG AFTERNOON THUNDERSTORM  
POTENTIAL ACROSS EASTERN TRINITY THROUGH WEDNESDAY AFTERNOON. SLIGHT  
CHANCES FOR THUNDERSTORMS WERE MAINTAINED THROUGH THE EXTENDED  
FORECAST, HOWEVER, I ONLY INCREASED POPS ON WEDNESDAY AFTERNOON  
SINCE THERE IS STILL SOME UNCERTAINTY IN THE MODELS WITH THE  
TRACKING OF THE CUT-OFF LOW. OTHERWISE WARM TEMPERATURES ACROSS  
INTERIOR AREAS WILL PERSIST INTO NEXT WEEK AS MODEL GUIDANCE TOOLS  
SHOW A HIGH PREDICTABILITY IN THE UPPER LEVEL RIDGE REMAINING  
STATIONED OVER THE WESTERN UNITED STATES. /KML  
 
AVIATION...NORTHERLY FLOW AND CLEARING SKIES HAS BEEN SPREADING  
SOUTHWARD ALONG THE OREGON COAST THROUGH THE DAY. THE CLEAR/DRY  
SLOT IN VISIBLE IMAGERY HAS BEEN ENTERING THE NORCAL COASTAL WATERS.  
HOWEVER SEVERAL SMALL SCALE VORTICES WERE PRESENT NEARSHORE FROM PT  
ST GEORGE TO PT ARENA. THIS DOES NOT BODE WELL FOR CLEARING SKIES  
ALONG THE COAST THIS EVENING. THUS EXPECT IFR CONDITIONS TO PREVAIL  
THROUGH THIS EVENING ALONG THE COAST. CONDITIONS SHOULD DETERIORATE  
TO LIFR AGAIN AND PUSH INTO THE NORTH COAST RIVER VALLEYS THIS  
EVENING AS WELL. A SHORTWAVE TROUGH MOVING THROUGH THE AREA TODAY WILL  
CONTINUE TO PRODUCE SCATTERED CBS AND ISOLATED TSTMS THROUGH EARLY  
EVENING OVER THE TRINITY COUNTY MTNS. ANOTHER VORT MAX WILL APPROACH  
ON THU AND EXPECT MORE INTERIOR CONVECTION.  
 
MARINE...THE PACIFIC RIDGE OF HIGH PRESSURE AND THE THERMAL TROUGH  
OVER CALIFORNIA WILL CONTINUE TO MAINTAIN MODERATE TO FRESH WINDS  
AND STEEP SEAS THROUGH THE WEEKEND. HIGHEST WINDS AND SEAS WILL BE  
FARTHER OFFSHORE. HOWEVER, AREAS NEARSHORE AROUND CAPE MENDOCINO  
AND POINT ARENA MAY OBSERVE HIGHER WINDS AND STEEPENING SEAS.  
OCCASIONAL GALE FORCE WINDS ARE POSSIBLE ACROSS THE OUTER WATERS  
THIS WEEKEND BUT DO NOT ANTICIPATE NEEDING A GALE WARNING AT THIS  
TIME SINCE CONDITIONS ARE FORECAST TO BE MARGINAL. AS FOR THE  
INNER WATERS, CONDITIONS WILL BE LOWER BUT STILL REMAIN STEEP WITH  
SOME AREAS REACHING SMALL CRAFT CRITERIA (ESPECIALLY NEAR CAPE  
MENDOCINO AND POINT ARENA). THE INNER WATERS WILL NEED TO BE  
MONITORED FOR ADVISORIES IF HIGH CONDITIONS SHOULD BECOME MORE  
WIDESPREAD. MODELS SHOW LITTLE CHANGES IN THE LARGER SCALE SURFACE  
PATTERN WITH EMBEDDED SHORTWAVES THAT MAY ALLOW THE PRESSURE  
GRADIENT TO EASE SLIGHTLY. SMALL CRAFT ADVISORIES FOR THE OUTER  
WATERS WILL LIKELY NEED TO BE EXTENDED INTO EARLY NEXT WEEK,  
HOWEVER, HELD OFF ON MAKING ANY CHANGES TO THE END TIME DUE TO  
UNCERTAINTY IN THE STRENGTH AND TIMING OF THE SHORTWAVES AND HOW  
THEY WILL EFFECT THE PRESSURE GRADIENT OFFSHORE. /KML  
 

 
   
EKA WATCHES/WARNINGS/ADVISORIES
 
 
CA...NONE.  
NORTHWEST CALIFORNIA COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 5 PM PDT SUNDAY PZZ470-475.  
 

 
 

 
 
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