390
FXUS66 KSEW 172323
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
323 PM PST FRI JAN 17 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 /TONIGHT THROUGH MONDAY/
AN UPPER-RIDGE CONTINUES
OFF THE COAST AS IT AXIS PUNCHES WELL INTO ALASKA. AT THE SURFACE,
A 1037 MB SURFACE HIGH IS SITTING JUST WEST OF HAIDA GWAII BUT ITS
INFLUENCE CAN BE FELT ACROSS THE REGION. HERE LOCALLY, HIGHER
PRESSURE ALONG WITH NORTHERLY FLOW ALOFT ARE MAINTAINING DRY AND
CHILLY WEATHER. FOR TONIGHT, THIS TREND WILL PERSIST AS TEMPS COOL
DOWN WITH WIDESPREAD 20S EXPECTED INTO SATURDAY MORNING.
ANOMALOUSLY COOL OVERNIGHT LOWS IN CONCERT WITH 20-25 MPH WIND
GUSTS ARE ENOUGH TO ALLOW THE ISSUANCE OF A COLD WEATHER ADVISORY
FOR THE LOWLANDS OF W WHATCOM COUNTY TONIGHT INTO SATURDAY
MORNING. APPARENT TEMPERATURES ARE FORECAST TO GET AS LOW AS 20 F
FOR THIS AREA DURING THIS TIME. HREF GUIDANCE HAS A 70% CHANCE OF
APPARENT TEMPS GETTING BELOW 21 F, FURTHER INCREASING CONFIDENCE. COLD
WEATHER MAY CAUSE IMPACTS TO VULNERABLE POPULATIONS,
INFRASTRUCTURE, ETC.
THE PATTERN WILL REMAIN LOCKED THROUGH THIS WEEKEND AS THE UPPER-
RIDGE SITS OFFSHORE. GUIDANCE HAS IT PROGRESSING GENTLY ON MONDAY
AS ITS AXIS BECOMES MORE IN LINE ACROSS THE PNW. DRY AND CALM CONDITIONS
ARE TO REMAIN THROUGHOUT THE SHORT-TERM FORECAST (BARRING A STRAY
SHOWER OR TWO). THE WEATHER MAY BE CALM, BUT ALSO COLD AS BELOW-
NORMAL TEMPERATURES CONTINUE. OVERNIGHT LOWS WILL FEATURE
WIDESPREAD 20S THROUGHOUT THIS PERIOD WITH DAYTIME HIGHS IN THE
LOWER 40S. CAN'T RULE OUT SPELLS OF PATCHY FOG DURING THE
NIGHTTIME AND MORNING HOURS.
LONG TERM /TUESDAY THROUGH FRIDAY/
LOWER HEIGHTS ARE FORECAST
TO REBOUND ALOFT ON TUESDAY AS A TRANSIENT SHORTWAVE PUSHES
THROUGH. WITH IT, A WEAK FRONT MAY DRAG ACROSS THE REGION AS
THE NBM HAS SLIGHT POPS RETURNING BY MIDWEEK. RIDGING LOOKS TO
REBOUND BY WEDNESDAY-THURSDAY BUT MUCH UNCERTAINTY EXISTS ON THE
EVOLUTION OF THE UPPER-LEVEL PATTERN GOING INTO FRIDAY.
REGARDLESS, THE NBM HAS LATCHED ON TO THIS UNCERTAINTY AND HAS
INTRODUCED POPS, ALBEIT WEAK ONES, STARTING WEDNESDAY AND CARRYING
THROUGH THE SECOND HALF OF THE NEW WEEK. BELOW NORMAL TEMPERATURES
ARE FAVORED FOR MUCH OF THE LONG TERM.
MCMILLIAN
AVIATION
AN UPPER LEVEL RIDGE OFFSHORE WILL GRADUALLY BUILD INTO
WESTERN WASHINGTON TODAY WITH NORTHWEST FLOW ALOFT CONTINUING. THIS
CONTINUES TO GRADUALLY ERODE WITH SCATTERING MID-LEVEL CLOUDS.
CLEARING SKIES AND MODEST SURFACE WINDS ALLOWING THE FOR THE
REDEVELOPMENT OF LIFR FOG/STRATUS TONIGHT ACROSS SOUTHERN PUGET
SOUND AND THE SOUTHWEST INTERIOR. CONFIDENCE IS NOTABLY LOWER FOR
THE CENTRAL/NORTHERN PUGET SOUND TERMINALS WHERE ENOUGH NORTHERLY
WIND, COUPLED WITH A LITTLE DRYING OF THE AIR MASS, MAY PRECLUDE
DEVELOPMENT. REGARDLESS, EXPECT CLOUD LAYER TO SCATTER FOR RETURN TO
VFR CONDITIONS AREA WIDE ON SATURDAY. BREEZY NORTHERLY OUTFLOW
THROUGH THE FRASER MAY MAINTAIN GUSTY WINDS AT TIMES ACROSS
PARTS OF WHATCOM COUNTY INCLUDING KBLI.
KSEA...LINGERING CLOUD DECK SCATTERS THIS EVENING WITH NORTHERLY
SURFACE WIND AROUND 10 KTS. TOUGH CALL ON FOG POTENTIAL AT THE
TERMINAL TONIGHT WITH LATEST GUIDANCE WITH A NON-NEGLIGIBLE CHANCE,
BUT PATTERN RECOGNITION SUGGEST THE BEST CHANCES WILL BE SOUTH AND
SOUTHWEST OF THE TERMINAL AREA. WILL KEEP LOWER CONDITIONS OUT OF
TAF FOR NOW BUT THE 11-14Z PERIOD IS THE TIME OF CONCERN TO MONITOR.
CULLEN
MARINE
HIGH PRESSURE CONTINUES TO BUILD OFFSHORE AND PUSH
OVER THE REGION INTO THE WEEKEND. OFFSHORE WINDS INCREASE A BIT AT
TIMES THIS WEEKEND, WITH GUSTY WINDS TO 20 KT POSSIBLE OVER PORTIONS
OF THE NORTHERN INTERIOR WATERS WITH OUTFLOW FROM THE FRASER.
ANOTHER ROUND POSSIBLE SUNDAY LATE. A WEAK SYSTEM WILL LIKELY FADE
OFFSHORE AS IT APPROACHES THE COASTAL WATERS AROUND TUESDAY, WITH A
RETURN OF HIGH PRESSURE AND RELATED OFFSHORE FLOW AROUND MIDWEEK.
THE NEXT STRONGER FRONTAL SYSTEM COULD APPROACH LATE NEXT WEEK. SEAS
WILL REMAIN BELOW 10 FEET THROUGH THE FORECAST PERIOD, THOUGH SEAS
WILL REMAIN MIXED WITH A NOTABLE LONG PERIOD WAVE GROUP AND A
SHORTER PERIOD GROUP BOTH PASSING THROUGH THE COASTAL WATERS THROUGH
THE WEEKEND. CULLEN
HYDROLOGY
NO RIVER FLOODING EXPECTED IN THE NEXT 7 DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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