603  
FXUS66 KEKA 251225  
AFDEKA  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE EUREKA CA  
425 AM PST SAT FEB 25 2017  
   
SYNOPSIS
 
SHOWER ACTIVITY SPREADING INLAND EARLY SATURDAY  
MORNING IS FORECAST TO DISSIPATE BY SATURDAY AFTERNOON. ANOTHER  
STORM SYSTEM WILL THEN ENTER THE REGION DURING SUNDAY, RESULTING  
IN ADDITIONAL SHOWER DEVELOPMENT AND HIGH ELEVATION SNOWFALL.  
SHOWERS WILL PERSIST GOING INTO EARLY NEXT WEEK, FOLLOWED BY A  
PERIOD OF WARMER AND DRIER WEATHER.  
 

 
   
DISCUSSION
 
A ZONE OF ENHANCED ASCENT ASSOCIATED WITH A  
SOUTHWARD MOVING TROUGH, AS WELL AS INCREASED LOW-LEVEL  
CONVERGENCE OCCURRING WITH AN OFFSHORE LOW PRESSURE CENTER, ARE  
AIDING IN THE DEVELOPMENT OF LOCALLY HEAVY TRAINING SHOWERS. THE  
MOST VIGOROUS SHOWER ACTIVITY IS SPREADING INLAND NEAR CAPE  
MENDOCINO, WITH ONE BAND OF SHOWERS PRODUCING AN INTRACLOUD  
LIGHTNING STRIKE (PER RECENT LIGHTNING DATA). THE LIGHTNING  
CONFIRMS THE CONVECTIVE ENVIRONMENT THESE SHOWERS ARE EMBEDDED  
WITHIN...WHICH IS MAINLY A RESULT OF COLD MIDLEVEL TEMPERATURES  
(NEAR -34 C AT 500 MB) AND LAPSE RATES FROM 7-8 C/KM IN THE LOW  
TO MIDLEVELS. THESE TRENDS SUGGEST THAT LOCALLY HEAVY SNOW IS  
PROBABLY OCCURRING ABOVE 2000 FEET OVER SOUTHWESTERN AND INTERIOR  
PORTIONS OF HUMBOLDT COUNTY. THUS, THE ONGOING WINTER WEATHER  
ADVISORY HAS BEEN MAINTAINED, THOUGH THE EXPIRATION TIME IS NOW  
18Z BASED ON SHORT TERM MODEL CONSENSUS SHOWING AN INCREASINGLY  
MARGINAL ENVIRONMENT FOR INLAND SHOWER DEVELOPMENT BY MIDDAY.  
 
MEANWHILE, WV IMAGERY SHOWS A VIGOROUS MIDLEVEL IMPULSE MOVING  
SOUTH ACROSS THE NRN AK PANHANDLE THIS MORNING. THIS IMPULSE IS  
FORECAST TO REACH COASTAL WA BY 12Z SUNDAY, AND THEN MOVE ACROSS  
FAR NRN CA BY 00Z MONDAY. SEVERAL WAVES OF ASCENT ARE FORECAST TO  
MOVE ACROSS DEL NORTE AND HUMBOLDT COUNTIES AS THIS TAKES  
PLACE...AND WITH LAPSE RATES STEEPENING ONCE AGAIN IN RESPONSE TO  
COLD MIDLEVEL TEMPERATURES, HEAVY SHOWER DEVELOPMENT WILL BE  
POSSIBLE. THESE SHOWERS WILL SPREAD ONSHORE BY MIDDAY SUNDAY, AND  
THEN TAPER OFF IN INTENSITY DURING SUNDAY NIGHT. IN ADDITION,  
CURRENT MODEL GUIDANCE INDICATES THE HEAVIEST QPF WITH THIS  
ACTIVITY WILL OCCUR OVER THE NORTHERN HALF OF THE CWA. THE  
RELATIVELY HEAVY PRECIPITATION COMBINED WITH SUBFREEZING  
MOUNTAIN/RIDGE-TOP TEMPERATURES WILL SUPPORT 12-HOUR SNOWFALL  
ACCUMULATIONS FROM 4-6 INCHES BETWEEN 18Z SUNDAY AND 06Z  
MONDAY...WHICH HAS PROMPTED A WINTER STORM WATCH ISSUANCE FOR  
LOCATIONS ABOVE 1500 FEET IN HUMBOLDT AND DEL NORTE COUNTIES.  
LIGHTER HIGH ELEVATION SNOW AMOUNTS ARE FORECAST TO OCCUR  
ELSEWHERE.  
 
COLD DEEP-LAYER NORTHERLIES ARE FORECAST TO PERSIST INTO EARLY  
NEXT WEEK, WHICH WILL AID IN SUFFICIENTLY STEEP LAPSE RATES FOR  
OCCASIONAL SHOWER DEVELOPMENT. MIDLEVEL RIDGING IS THEN FORECAST  
TO OCCUR OVER THE NERN PAC BY MIDWEEK, WHICH WILL SHUNT COLD AIR  
ALOFT TO THE EAST. LARGE-SCALE SUBSIDENCE WILL ALSO DEVELOP OVER  
THE REGION...THE END RESULT BEING AN EXTENDED PERIOD OF DRY  
WEATHER OCCURRING DURING MID TO LATE NEXT WEEK, AND ALSO  
POTENTIALLY WARMER SURFACE TEMPERATURES.  
 

 
   
AVIATION
 
OVERNIGHT, SHOWERS WERE IMPACTING ALL TERMINALS AS  
THE LOW PRESSURE DROPPED SOUTH ALONG THE COAST AND BROUGHT IN  
COOLER AND MORE UNSTABLE AIRMASS INTO THE AREA. THE SHOWERS CAN  
POTENTIALLY LOWER CONDITIONS DOWN TO MVFR. DO EXPECT THE SHOWER  
ACTIVITIES TO TAPER OFF BY MID MORNING, AS THE LOW CONTINUES TO  
DRIFT SOUTH OF THE AREA. CLEARING SKIES WILL TAKE PLACE IN THE  
LATE MORNING HOURS, SHOULD TURN OUT TO BE A NICE AFTERNOON. FOR  
OVERNIGHT TONIGHT, DON'T EXPECT MUCH CLOUDS TO FORM, AS THE  
NORTHERLIES SHOULD BE STRONG ENOUGH TO BRING IN ENOUGH DRY AIR TO  
KEEP THE SKY COVER TO A MINIMUM. /RCL  
 

 
   
MARINE
 
A COMPACT LOW, CURRENTLY OFF THE NW CALIFORNIA COAST,  
IS MAKING ITS SOUTHWARD TREK. EARLY THIS MORNING, LIGHT TO  
MODERATE SOUTHERLIES WERE FOUND ON THE COASTAL WATERS. AS THE LOW  
MOVED SOUTH OF THE AREA, THE WINDS WILL SHIFT TO THE NORTH LATER  
THIS AFTERNOON AND EVENING. THE NORTHERLY WINDS WILL STICK AROUND  
THROUGH SUNDAY MORNING, THEN SHIFTING TO THE WEST WITH THE ADVANCE  
OF THE NEXT LOW PRESSURE SYSTEM.  
 
ON SUNDAY MORNING, THE NEXT SYSTEM WILL BE OVER THE OLYMPIC  
PENINSULA. THE MAIN LOW WILL REMAIN NORTH OF OUR AREA. FOR US, WE  
WILL BE SEEING MOSTLY WEST TO NORTHWEST WINDS IN OUR COASTAL  
WATERS FOR SUNDAY. AFTER THAT, WINDS WILL SHIFT TO THE NORTH, AND  
PERSIST THROUGH END OF THE WORK WEEK.  
 
SEAS WILL REMAIN FAIRLY LOW, AROUND 7 TO 8 FEET. THERE WILL BE  
TIME PERIODS WHEN THE SEAS WILL GO UP TO 9 TO 10 FEET AT TIMES  
WITH THE OCCASIONAL INCREASE IN NORTHERLY WINDS.  
 
NO MARINE HAZARDS ARE IN EFFECT AT THIS TIME. /RCL  
   
SNEAKER WAVE POTENTIAL
 
MODELS ARE INDICATING THERE IS A  
MODERATE POSSIBILITY FOR SNEAKER WAVES TO OCCUR ALONG COASTAL  
BEACHES FROM EARLY SUNDAY MORNING THROUGH SUNDAY AFTERNOON.  
HOWEVER, THE MODELS ARE STILL WORKING ON FINE TUNING THE TIMING  
OF THIS EVENT. HAVE ISSUED A BEACH HAZARD STATEMENT TO HIGHLIGHT  
THIS POTENTIAL HAZARD. /RCL  
 

 
   
EKA WATCHES/WARNINGS/ADVISORIES
 
 
CA...BEACH HAZARDS STATEMENT FROM LATE TONIGHT THROUGH SUNDAY  
AFTERNOON FOR CAZ101-103-104-109.  
 
WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR CAZ102-  
104>106-108-110.  
 
WINTER STORM WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING  
FOR CAZ102-105.  
 
NORTHWEST CALIFORNIA COASTAL WATERS...BEACH HAZARDS STATEMENT FROM LATE  
TONIGHT THROUGH SUNDAY AFTERNOON FOR PZZ410.  
 

 
 

 
 
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