566  
FXUS66 KEKA 191137  
AFDEKA  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE EUREKA CA  
437 AM PDT THU JUL 19 2018  
   
SYNOPSIS
 
HOT TEMPERATURES ARE LIKELY ACROSS INTERIOR VALLEYS  
TODAY, FOLLOWED BY SLIGHTLY COOLER CONDITIONS DURING THE WEEKEND.  
OTHERWISE, ISOLATED THUNDERSTORMS WILL BE POSSIBLE FRIDAY  
AFTERNOON THROUGH SUNDAY ACROSS PORTIONS OF MENDOCINO AND TRINITY  
COUNTIES.  
 

 
   
DISCUSSION
 
HOT AFTERNOON TEMPERATURES FROM 100 TO 110 ARE  
FORECAST TO OCCUR ACROSS TRINITY AND INTERIOR MENDOCINO COUNTIES  
THIS AFTERNOON...FOLLOWED BY A SLIGHT COOL DOWN GOING INTO THE  
WEEKEND. REFERENCE THE LATEST HEAT ADVISORY STATEMENT FOR  
ADDITIONAL INFORMATION ON ELEVATED HEAT RISK CONDITIONS OVER THE  
INTERIOR.  
 
OTHERWISE, AN UPPER-LEVEL ANTICYCLONE WAS POSITIONED OVER THE  
SOUTHERN GREAT BASIN/FOUR CORNERS REGION EARLY THURSDAY MORNING,  
WITH SUB-TROPICAL MOISTURE, CHARACTERIZED BY PW VALUES FROM  
1.5-2.0 INCHES, SPREADING WEST-NORTHWEST ACROSS SOUTHERN  
CALIFORNIA. THE UPPER HIGH IS FORECAST TO BECOME RE-CENTERED OVER  
THE SOUTHERN HIGH PLAINS BY FRIDAY NIGHT, WHICH WILL YIELD  
MIDLEVEL SOUTHERLIES OVER CA, AND SUBSEQUENTLY ALLOW PW VALUES  
FROM 1.0-1.5 INCHES TO SPREAD NORTH TOWARD MENDOCINO COUNTY. THIS  
MOISTURE COMBINED WITH STEEP MID/UPPER-LEVEL LAPSE RATES WILL  
RESULT IN A MARGINALLY UNSTABLE AIRMASS, WITH MUCAPE VALUES  
RANGING FROM 200 TO LOCALLY 1000 J/KG (BASED ON NAM OUTPUT)  
EMANATING FROM A LIFTED PARCEL NEAR 700 MB. THIS THERMODYNAMIC  
ENVIRONMENT COMBINED WITH MODEST MIDLEVEL CONVERGENCE AND  
ISENTROPIC UPGLIDE MAY BE SUFFICIENT FOR A FEW ELEVATED  
THUNDERSTORMS (MAINLY OVER MENDOCINO COUNTY) FRIDAY NIGHT.  
 
SUBTROPICAL MOISTURE IS FORECAST TO SPREAD NORTH ACROSS THE  
REMAINDER OF NWRN CA DURING THE WEEKEND. STRONG HEATING AND A  
STEEP LAPSE RATE ENVIRONMENT WILL DEVELOP ACROSS THE INTERIOR  
MOUNTAINS SATURDAY AND SUNDAY AFTERNOONS, WHICH WILL SUPPORT  
ADDITIONAL ISOLATED THUNDERSTORM DEVELOPMENT FROM NORTHEASTERN  
MENDOCINO COUNTY NORTH ACROSS TRINITY COUNTY.  
 
FOLLOWING THE WEEKEND, AN UPPER HIGH IS FORECAST TO BECOME  
CENTERED OVER THE COLORADO PLATEAU AND SOUTHERN GREAT BASIN BY  
MIDWEEK. INTENSE AFTERNOON HEATING WILL BECOME PROBABLE ONCE AGAIN  
ACROSS THE INTERIOR, WITH HIGH TEMPERATURES AT OR ABOVE 100 F  
DEVELOPING ACROSS THE VALLEYS OF MENDOCINO AND TRINITY COUNTIES  
TUESDAY, WEDNESDAY, AND THURSDAY.  
 

 
   
AVIATION
 
LOW CLOUDS AND SOME LIGHT FOG HAVE DEVELOPED ONCE  
AGAIN ALONG PORTIONS OF THE REDWOOD COAST. HOWEVER, CLOUDS ARE NOT  
AS EXPANSIVE OVER THE ADJACENT COASTAL WATERS AS THE PAST FEW  
DAYS. IN ADDITION, THE MARINE LAYER IS A BIT SHALLOWER AND  
FORECAST TO BECOME MORE SO OVER THE NEXT 24 HOURS. ADDITIONALLY, N  
WINDS HAVE INCREASED OVER THE COASTAL WATERS, WITH DECREASES IN  
CLOUDINESS DOWNSTREAM FROM CAPE BLANCO AND AN OFFSHORE COMPONENT  
TO THE LOW-LEVEL WIND FLOW FORECAST FOR COASTAL DEL NORTE COUNTY.  
ALL THIS POINTS TO LESS COASTAL CLOUDINESS AND FASTER IMPROVEMENT  
IN CEILINGS AT KCEC AND KACV THIS MORNING. HIGH RESOLUTION MODELS  
SHOW SOME LINGERING CLOUDINESS NEAR AND JUST N OF CAPE MENDOCINO,  
AND THIS MAY OCCASIONALLY AFFECT THE IMMEDIATE COAST FROM HUMBOLDT  
BAY S TO THE CAPE. WINDS OVER LAND WILL BE GENERALLY LIGHT, WITH  
GUSTS NEAR 20 KNOTS DURING THE AFTERNOON AT KCEC. VFR CONDITIONS  
ARE EXPECTED TO CONTINUE AT KUKI. /SEC  
 

 
   
MARINE
 
NORTHERLY WINDS WILL CONTINUE TO INCREASE TODAY. A GALE  
WARNING REMAINS IN EFFECT FOR THE N OUTER WATERS FOR FREQUENT  
WIND GUSTS OVER 35 KNOTS. THE GALE WARNING FOR THE S OUTER WATERS  
GOES INTO EFFECT AROUND MIDDAY TODAY, WITH CONDITIONS MORE  
MARGINAL IN THAT AREA. THE STRONGEST WINDS WILL BE OVER THE N  
PORTION OF THE ZONE AS WELL AS WITHIN THE EXPANSION FAN DOWNWIND  
OF CAPE MENDOCINO. SEAS WILL BUILD TO 12 TO 15 FEET IN THE OUTER  
WATERS TODAY. CONDITIONS WILL SLOWLY IMPROVE LATE IN THE WEEKEND  
AS THE INLAND THERMAL TROUGH PIVOTS TO A MORE NE TO SW  
ORIENTATION. HOWEVER, A HAZARDOUS SEAS WARNING MAY BE REQUIRED FOR  
A PORTION OF THE MARINE WATERS AFTER THE GALES BEGIN TO SUBSIDE.  
/SEC  
 

 
   
FIRE WEATHER
 
WEAK LOW PRESSURE IS FORECAST TO DEVELOP OFFSHORE  
FROM SAN FRANCISCO DURING THE NEXT 24-36 HOURS. AS THAT OCCURS,  
RIDGETOP WINDS WILL TAKE ON AN EASTERLY COMPONENT, AND LOCALLY  
BECOME GUSTY OVER THE MOUNTAINS OF DEL NORTE COUNTY. THIS WILL  
RESULT IN AREAS OF ELEVATED FIRE WEATHER CONDITIONS...BUT A RED  
FLAG WARNING DOES NOT APPEAR WARRANTED AT THIS TIME DUE TO  
MARGINAL RH VALUES OCCURRING DURING THE PERIOD OF STRONGEST WINDS.  
 
OTHERWISE, MODEL GUIDANCE SHOWS MONSOON MOISTURE SPREADING NORTH  
TO AT LEAST MENDOCINO COUNTY BY FRIDAY NIGHT. MODEST MUCAPE,  
LOCALLY NEAR 1000 J/KG, IS FORECAST TO BE ROOTED NEAR 700 MB.  
THE POTENTIALLY UNSTABLE ATMOSPHERE COMBINED WITH MIDLEVEL  
CONVERGENCE AND ISENTROPIC UPGLIDE MAY BE SUFFICIENT FOR ISOLATED  
ELEVATED THUNDERSTORM DEVELOPMENT FRIDAY NIGHT. THEREAFTER,  
SURFACE BASED THUNDERSTORM DEVELOPMENT BECOMES MORE PROBABLE  
SATURDAY AFTERNOON, AND AGAIN SUNDAY AFTERNOON, OVER TRINITY AND  
NORTHEASTERN MENDOCINO COUNTIES.  
 

 
   
EKA WATCHES/WARNINGS/ADVISORIES
 
 
CA...HEAT ADVISORY UNTIL 9 PM PDT THIS EVENING FOR CAZ107-108-110-111-  
113.  
 
NORTHWEST CALIFORNIA COASTAL WATERS...GALE WARNING UNTIL 4 AM PDT  
SATURDAY FOR PZZ470.  
 
SMALL CRAFT ADVISORY UNTIL 4 AM PDT FRIDAY FOR PZZ455.  
 
SMALL CRAFT ADVISORY UNTIL 4 AM PDT SATURDAY FOR PZZ450.  
 
SMALL CRAFT ADVISORY UNTIL 11 AM PDT THIS MORNING FOR PZZ475.  
 
GALE WARNING FROM 11 AM THIS MORNING TO 4 AM PDT FRIDAY FOR  
PZZ475.  
 

 
 

 
 
VISIT US AT HTTP://WWW.WEATHER.GOV/EUREKA  
 
FOLLOW US ON FACEBOOK AND TWITTER AT:  
HTTP://WWW.FACEBOOK.COM/NWSEUREKA  
HTTP://WWW.TWITTER.COM/NWSEUREKA  
 
FOR FORECAST ZONE INFORMATION  
SEE THE FORECAST ZONE MAP ONLINE:  
HTTP://WWW.WEATHER.GOV/EUREKA/ZONEMAP.PNG  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab CA Page Main Text Page