694
FXUS66 KSEW 181054
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
255 AM PST SAT JAN 18 2025
SYNOPSIS
HIGH PRESSURE WILL DOMINATE THE WEATHER INTO THE
MIDDLE OF NEXT WEEK, BRINGING DRY CONDITIONS AND COLDER
TEMPERATURES. OVERNIGHT LOWS ARE EXPECTED TO FALL BELOW FREEZING
OVER MUCH OF WESTERN WASHINGTON THIS WEEKEND AND INTO NEXT WEEK.
SHORT TERM /TODAY THROUGH MONDAY/
WHILE REPETITIVE, ONCE AGAIN W
WA IS SEEING SOME PATCHY FOG...THOUGH NOT QUITE AS WIDESPREAD AS 24
HOURS AGO...AND MOST OBS SITES REPORTING SUB-FREEZING TEMPS. AS OF 2
AM PST, THE ONLY SITE TO SHOW TEMPS ABOVE 32 IS BREMERTON, ALL OTHER
SITES RANGING IN THE UPPER 20S TO LOWER 30S. THAT SAID, WITH TEMPS
IN BELLINGHAM SITTING AROUND 26-27 DEGREES AND CALM WINDS, NOT
ENTIRELY SURE THAT COLD WEATHER ADVISORY IN PLACE FOR WESTERN
WHATCOM COUNTY WILL MEET CRITERIA...BUT WITH A FEW MORE HOURS OF
COOLING AHEAD, IT MAY YET BE POSSIBLE, ESPECIALLY IF NE WINDS THERE
RE-EMERGE. THAT SAID, WILL LEAVE INHERITED HEADLINE IN PLACE FOR THE
MORNING FORECAST PACKAGE.
THIS DISCUSSION WILL ECHO THOSE OF THE RECENT PAST AS CURRENT
WEATHER PATTERN HAS NOT CHANGED VERY MUCH. W WA STILL FINDS ITSELF
UNDER THE INFLUENCE OF UPPER LEVEL RIDGING, THE MAIN AXIS OF WHICH
WILL NOT EVEN MAKE IT TO THE COAST UNTIL LATE SUNDAY NIGHT/EARLY
MONDAY MORNING. THIS WILL ALLOW FOR CONTINUED DRY CONDITIONS AND
COOLER TEMPERATURES...BECOMING DOWNRIGHT COLD OVERNIGHT AS SUB-
FREEZING OVERNIGHT TEMPS REMAIN IN THE FORECAST FOR THE ENTIRE NEAR
TERM PERIOD. THE ONLY DIFFERENCE THAT IS WORTH POINTING OUT IN THE
SHORT TERM IS THAT ANY OVERNIGHT/EARLY MORNING FOG WILL BECOME
INCREASINGLY LIMITED AS THE ATMOSPHERE CONTINUES TO DRY FURTHER,
WITH THE EXPECTATION THAT ANY PROSPECTS FOR FOG SHOULD BE GONE BY
SUNDAY NIGHT. DAYTIME HIGH TEMPS WILL REMAIN FAIRLY STATIC IN THE
NEAR TERM REMAINING IN THE LOWER 40S FOR MOST LOWLAND LOCATIONS.
THIS WILL KEEP THE AREA AROUND 7-8 DEGREES COLDER THAN NORMAL. THE
BIGGER STORY WILL BE OVERNIGHT LOWS, WHERE ADDITIONAL, YET SLIGHT,
COOLING IS STILL EXPECTED. TONIGHT WILL SEE LOWS SOLIDLY IN THE MID
TO UPPER 20S, SUNDAY NIGHT WILL BE SLIGHTLY COLDER WITH NO REAL
CHANGE IN THE RANGE BUT ON AVERAGE 2 OR 3 DEGREES LOWER. MONDAY
NIGHT SHOWS AT LEAST A SLIGHT IMPROVEMENT AS LOWS WILL RANGE IN THE
MID 20S TO AROUND 30. WITH TEMPS THIS COLD, SOME CONSIDERATION HAS
TO BE GIVEN TO ADDITIONAL COLD WEATHER ADVISORIES IN THE NEAR TERM,
HOWEVER THE UPPER LEVEL RIDGE WILL ACTUALLY PROVE TO HELP TO
MINIMIZE WINDS AND THUS NOT ALLOWING APPARENT TEMP /TEMP AND WIND
CHILL/ TO VARY TOO FAR AWAY FROM ACTUAL TEMPERATURE. THIS SHOULD
KEEP CONDITIONS JUST OUTSIDE OF ADVISORY CRITERIA AND AS SUCH, WILL
NOT OPT FOR ANY ADDITIONAL HEADLINES AT THIS TIME. ALL OF THIS UNDER
THE CAVEAT THAT SHOULD FUTURE FORECAST UP THE WINDS EVEN
INCREMENTALLY, THIS STANCE WILL NEED TO BE RECONSIDERED.
18
LONG TERM /TUESDAY THROUGH FRIDAY/
THE RIDGE BEGINS TO WEAKEN
LATE MONDAY NIGHT/EARLY TUESDAY MORNING IN ADVANCE OF AN APPROACHING
SHORTWAVE TROUGH. NEITHER OF THE DETERMINISTIC MODELS ARE IMPRESSED
WITH THE FEATURE, HAVING ANY MOISTURE ASSOCIATED WITH IT FIZZLING
OUT BEFORE EVEN REACHING THE COAST. ALTHOUGH THIS DOES PUT THE
KIBOSH ON ANY PRECIP CHANCES, ENOUGH CLOUD COVER WILL MOVE INTO THE
AREA TO GIVE OVERNIGHT TEMPS A SLIGHT INCREASE, RANGING IN THE UPPER
20S TO LOWER 30S. ALAS, MOST LOCATIONS WILL REMAIN SUB-FREEZING,
HOWEVER THIS SHOULD KEEP CONDITIONS JUST NORTH OF ANY ADVISORY
CRITERIA. ANOTHER UPPER LEVEL RIDGE SHIFTS INLAND WEDNESDAY AND MOST
OF THURSDAY. THIS KEEPS CONDITIONS DRY AND MAYBE A SLIGHT
MODIFICATION TO TEMPERATURES AS BOTH DAYTIME HIGHS AND OVERNIGHT
LOWS WARM A TAD. HIGHS THESE TWO DAYS SHOULD FALL MORE SOLIDLY IN
THE MID 40S FOR MOST SPOTS AND THIS WILL BE THE FIRST OPPORTUNITY
FOR SOME LOCATIONS TO SEE OVERNIGHT LOWS ABOVE FREEZING AS TEMPS
WILL RANGE IN THE LOWER TO MID 30S. THE CAUSE FOR MINOR WARMING IS
HINTED AT IN THE ECMWF AS THE RIDGE AMPLITUDE IS NOT QUITE AS
PRONOUNCED, ALLOWING FOR SYSTEMS PASSING OVER THE TOP OF THE FEATURE
TO DIP DOWN INTO SOUTHERN BC. FOR THE MOST PART, THE MAIN IMPACT FOR
W WA WILL BE ANOTHER INCREASE IN CLOUDS, HOWEVER THE NBM, AS IT IS
PROVING WONT TO DO, HAS LATCHED ONTO MORE THE UNCERTAINTY OF THESE
SOLUTIONS, PAINTING SOME PRETTY LOW CONFIDENCE POPS FOR THE ENTIRE
SECOND HALF OF THE WEEK...EVEN THOUGH THE STRONGEST INDICATIONS OF A
FOLLOW-UP SYSTEM LEAN MORE TOWARD THE LATE THURSDAY INTO FRIDAY TIME
FRAME. THE BETTER REFLECTION OF WHAT IS MOST LIKELY TO HAPPEN ONCE
AGAIN COMES FROM THE ENSEMBLES, WHO HAVE TO THIS POINT PRETTY
CONSISTENTLY POO-POOED THE CHANCES OF PRECIP AT THE END OF THE
EXTENDED...TOPPING POPS OUT AROUND 30 PCT WHILE MAINTAINING A MEAN
WELL BELOW THAT AT AROUND 10 PCT.
18
AVIATION
UPPER LEVEL RIDGING SITUATED OFFSHORE WILL MAINTAIN
NORTHWESTERLY FLOW ALOFT THROUGH THE TAF PERIOD. CLEARING HAS LED
TO SOME REDEVELOPMENT OF FOG AND EVEN SOME FREEZING FOG OVERNIGHT
ACROSS PORTIONS OF THE CENTRAL AND SOUTH SOUND. CONDITIONS AT
AREA TERMINALS WILL LIKELY DROP DOWN TO IFR/LIFR OVER THE NEXT FEW
HOURS IN FOG. TERMINALS THAT STAY OUT OF THE FOG WILL REMAIN VFR
TO MVFR. AREAS OF MORNING FOG WILL LIFT AND SCATTER BETWEEN
18-21Z. WINDS HAVE GENERALLY BECOME CALM OVERNIGHT, THOUGH WILL
INCREASE OUT OF THE NORTH THIS MORNING AND PERSIST AT 4-8 KT. NE
WINDS FOR KBLI MAY BE GUSTY AT TIMES UP TO 20 KT THROUGH THE
MORNING HOURS. ANOTHER ROUND OF FOG DEVELOPMENT IS POSSIBLE
TONIGHT INTO EARLY SUNDAY.
KSEA...VFR CONDITIONS IN CLEAR SKIES. EXPECT IFR/LIFR CONDITIONS
TO DEVELOP SHOULD FOG MAKE IT INTO THE TERMINAL FROM THE NORTH.
WINDS HAVE CALMED OVERNIGHT, THOUGH WILL INCREASE OUT OF THE NORTH
THIS MORNING AND PERSIST AT 4-8 KT. FOG WILL SCATTER BETWEEN
18-21Z THIS MORNING FOR VFR CONDITIONS THIS AFTERNOON AND EVENING.
14
MARINE
HIGH PRESSURE WILL CONTINUE TO BUILD OFFSHORE AND MOVE
INTO THE REGION THIS WEEKEND. OFFSHORE WINDS WILL PERSIST AS A
RESULT, BECOMING GUSTY TO 20 KT AT TIMES TODAY AND SUNDAY ALONG
THE NORTHERN INLAND WATERS AND THE STRAIT OF JUAN DE FUCA DUE TO
WEAK FRASER OUTFLOW. A FRONTAL SYSTEM LOOKS TO APPROACH THE
REGION ON TUESDAY AND DISSIPATE JUST OFFSHORE VANCOUVER ISLAND,
BRINGING NO SIGNIFICANT IMPACT TO THE AREA WATERS. HIGH PRESSURE
WILL THEN REBUILD INTO THE COASTAL WATERS AROUND MIDWEEK FOR
ANOTHER ROUND OF OFFSHORE FLOW. A MORE SIGNIFICANT FRONTAL SYSTEM
MAY APPROACH BY FRIDAY. SEAS GENERALLY LOOK TO HOVER BETWEEN 6-8
FT INTO EARLY NEXT WEEK, THOUGH LOOK TO REMAIN MIXED THROUGH THE
WEEKEND AS A LONGER PERIOD WAVE GROUP INTERACTS WITH A SHORTER
PERIOD WAVE GROUP. SEAS LOOK TO SUBSIDE TOWARDS 3-5 FT BY MIDWEEK.
14
HYDROLOGY
NO RIVER FLOODING EXPECTED IN THE NEXT 7 DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...COLD WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR WESTERN
WHATCOM COUNTY.
PZ...NONE.
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